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Dimethylsulfoniopropionate (DMSP) is one of Earth's most abundant organosulfur compounds with important roles in stress tolerance, chemotaxis, global carbon and sulfur cycling, and climate-active gas production. Diverse marine prokaryotes and eukaryotes produce DMSP via three known pathways (methylation, transamination, and decarboxylation) and metabolize DMSP via three further pathways (demethylation, cleavage, and oxidation). Over 20 key enzymes from these pathways have been identified that demonstrate the biodiversity and importance of DMSP cycling. The last dozen years have seen significant changes in our understanding of the enzymology and molecular mechanisms of these DMSP cycling enzymes through the application of biochemistry and structural biology. This has yielded more than 10 crystal structures and, in many cases, detailed explanations as to how and why organisms synthesis and metabolize DMSP. In this review, we describe recent progress in biochemical and mechanistic understandings of DMSP synthesis and metabolism, highlighting the important knowledge gleaned and current challenges that warrant further exploration. [ABSTRACT FROM AUTHOR]

Dimethylsulfoniopropionate (DMSP) is one of the most important organic sulfur compounds on Earth, and its significance in global sulfur cycling and climate regulation cannot be overlooked, as it plays an indispensable role in these processes. Phytoplankton are the major producers of DMSP in the marine environment, and nitrogen nutrients are key factors influencing the production of DMSP in phytoplankton. This study focused on two algal species, Emiliania huxleyi (a high DMSP producer) and Phaeodactylum tricornutum (a medium DMSP producer), and conducted indoor culture experiments to compare and analyze the content of particulate DMSP (DMSPp) in the algal culture media under different nitrogen nutrient concentrations and types. The study investigated the relationships between overall DMSPp content, algal density, and DMSPp content per individual algal cell. The results indicated that different nitrogen nutrient concentrations and types had a minimal impact on the content of DMSPp per individual cell in E. huxleyi (P > 0.05), suggesting that the DMSPp concentration in the culture media was mostly influenced by algal cell density. Conversely, different nitrogen nutrient concentrations and types had a significant impact on the content of DMSPp per individual cell in P. tricornutum (P < 0.05), indicating that the DMSPp concentration in the culture media was mainly influenced by the content of DMSPp per individual algal cell. For instance, in the case of P. tricornutum, the average DMSPp content per individual cell in the low NO3– concentration (0 μmol/L) culture group was 11 times greater than that in the high NO3– concentration (1 764 μmol/L) culture group. Furthermore, under different nitrogen nutrient types, the average total DMSPp concentration in NaNO3 culture media was three and four times higher than that in the NH4Cl and CH4N2O culture groups, respectively. These differences may be attributed to variations in the physiological effects of DMSP on different algal species.

When emersed, intertidal seaweeds experience rapid changes in environmental conditions. On warm sunny days, seaweeds can desiccate soon after emersion. On rainy days or in areas with freshwater inputs, they may experience rapid drops in salinity. To determine whether one low tide's exposure to environmental stress alters seaweed growth, palatability to herbivores, and dimethylsulfoniopropionate (DMSP) concentrations, we exposed Ulva fenestrata to desiccation and hyposaline conditions for 3 h in summer and winter. Two days later, summer desiccation decreased growth, consumption by Lacuna vincta, and DMSP by 71%, 83%, and 67%, relative to controls. Winter desiccation reduced DMSP by 19% and did not affect growth or L. vincta feeding. Summer hyposaline conditions increased growth by 75% but did not affect L. vincta grazing or DMSP, whereas winter hyposaline conditions reduced growth by 37%. After 2 days of exposure to L. vincta, seaweeds were allowed to recover for 7 days, then DMSP was measured. U. fenestrata desiccated in the summer did not survive. Average DMSP concentrations were 127% higher in grazed than ungrazed seaweed in the summer salinity experiment, providing evidence that grazing induces DMSP. No DMSP induction occurred in winter, possibly because grazing rates were much lower. In a follow-up summer desiccation experiment, maximum quantum yields (MQYs) and DMSP decreased to 12% and 14% of controls within an hour. After 7 days, MQY and DMSP concentrations recovered, but growth was 81–97% lower in seaweeds desiccated for 30–60 min, relative to controls. These results provide the first evidence for grazer-induced DMSP increases. [ABSTRACT FROM AUTHOR]

Phaeocystis antarctica forms extensive spring blooms in the Southern Ocean that coincide with high concentrations of dimethylsulfoniopropionate (DMSP), dimethylsulfoxide (DMSO), dimethylsulfide (DMS), and acrylate. We determined how concentrations of these compounds changed during the growth of axenic P. antarctica cultures exposed to light‐limiting, sub‐saturating, and saturating PAR irradiances. Cellular DMSP concentrations per liter cell volume (CV) ranged between 199 and 403 mmol · LCV−1, with the highest concentrations observed under light‐limiting PAR. Cellular acrylate concentrations did not change appreciably with a change in irradiance level or growth, ranging between 18 and 45 mmol · LCV−1, constituting an estimated 0.2%–2.8% of cellular carbon. Both dissolved acrylate and DMSO increased substantially with irradiance during exponential growth on a per‐cell basis, ranging from 0.91 to 3.15 and 0.24 to 1.39 fmol · cell−1, respectively, indicating substantial export of these compounds into the dissolved phase. Average cellular DMSO:DMSP ratios increased 7.6‐fold between exponential and stationary phases of batch growth, with a 3‐ to 13‐fold increase in cellular DMSO likely formed from abiotic reactions of DMSP and DMS with reactive oxygen species (ROS). At mM levels, cellular DMSP and acrylate are proposed to serve as de facto antioxidants in P. antarctica not regulated by oxidative stress or changes in ROS. Instead, cellular DMSP concentrations are likely controlled by other physiological processes including an overflow mechanism to remove excess carbon via acrylate, DMS, and DMSO during times of unbalanced growth brought on by physical stress or nutrient limitation. Together, these compounds should aid P. antarctica in adapting to a range of PAR irradiances by maintaining cellular functions and reducing oxidative stress. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive study of biogenic dimethylated sulfur compounds and methane (CH4) from 27 March to 16 April 2018 (spring) and from 24 July to 10 August 2018 (summer) in the Yellow Sea and Bohai Sea. The overall distributions of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP, precursor of DMS), dimethylsulfoxide (DMSO, oxidation product of DMS) and CH4 in surface waters were characterized by elevated concentrations in summer and in coastal waters, coupled to phytoplankton biomass and terrestrially sourced inputs. Surface waters were oversaturated with CH4. The flux distributions of DMS and CH4 were generally consistent with their concentration distributions. In situ incubation experiments revealed that microbial consumption was the main removal mechanism for DMS, which could remove up to 72.1% of the total DMS compared to sea‐to‐air exchange in the surface layer. High DMS release and enhanced DMS yields (34%–62%) suggested more obvious influence from high DMSP concentrations (1 or 5 μm L−1) on DMS production in oligotrophic waters with lower bacterial sulfur demand in contrast to near‐shore waters. Positive correlations were found between CH4 and DMSP (dissolved) in summer and DMSO (particulate and dissolved) in spring. A DMSP addition experiment suggested that DMSP could act as a precursor for aerobic methanogenesis, and CH4 preferentially occurs under nitrogen‐stressed conditions in the surface layers of the Yellow Sea and Bohai Sea. Plain Language Summary: Dimethylated sulfur (DMS) is considered to be a cooling‐effect biogenic gas derived from the decomposition of dimethylsulfoniopropionate (DMSP). DMSP is associated with the aerobic production of methane (CH4), a powerful greenhouse gas with global warming potential. Oceanic emission remains a highly uncertain term in the budgets of atmospheric CH4 and DMS because of sparse sampling and the variable marine environment. In order to clarify their key biogeochemical processes and provide more field data for quantifying global and regional budgets, distributions and emission fluxes of DMS and CH4, and possible CH4 production from DMSP in upper waters, were investigated in the Yellow Sea and Bohai Sea. Biogenic dimethylated sulfur compounds including DMS, DMSP, dimethylsulfoxide (the oxidation product of DMS), and CH4 exhibited high concentrations in summer and in coastal waters mainly due to the influence of phytoplankton biomass and terrestrial sources. Surface waters were oversaturated with CH4, and the flux distributions of DMS and CH4 generally followed their concentration distributions. High levels of DMSP had a more obvious influence on DMS emission in offshore waters because of various microbial demands. CH4 was found to be produced from DMSP in oxic waters, especially in offshore waters with nitrate limitation. Key Points: Dimethylsulfoniopropionate (DMSP)‐dependent methane production preferentially occurs under nitrate limitation in the offshore waters of the Yellow Sea and Bohai SeaThe distributions of the sea‐to‐air flux of dimethylsulfide (DMS) and CH4 are consistent with their concentrations in surface watersHigh levels of DMSP have a more obvious influence on DMS release in offshore waters with lower sulfur demand compared to near‐shore waters [ABSTRACT FROM AUTHOR]

Dimethyl sulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) are ubiquitous sulfur compounds in the ocean. DMS is emitted into the atmosphere and has potential climatic effects. The distributions of DMS and DMSP are affected by various biological factors (i.e., bacterial catabolism and phytoplankton and zooplankton community composition). The horizontal and vertical distributions of DMSP, DMSP lyase activity (DLA), DMS, and the abundances of bacteria, DMSP‐consuming bacteria, dimethyl sulfoxide‐consuming bacteria, and picophytoplankton were investigated in the Bohai Sea (BS) and Yellow Sea (YS) during autumn 2020. DLA was significantly correlated with chlorophyll a, DMS, and dissolved DMSP concentrations. Our data show that bacteria Clade_I SAR11 was a significant contributor to DLA. A dilution experiment indicated that the highest microzooplankton grazing rate coincided with the highest DMS concentration and DMS production rate. A proportion of 16%–62% of the DMSPt was converted to DMS in the dilution experiment. Copepods dominated the mesozooplankton community. Calanus sinicus was the predominant copepod in the BS and YS. C. sinicus grazing stimulated DMS production. DMS concentration increased 299% after C. sinicus grazing on physically broken algal cells for 48 hr. These results will help with a better understanding of the control of DMS and DMSP concentrations by zooplankton and the DMS release mechanisms that occur through zooplankton grazing. Plain Language Summary: Dimethylsulfoniopropionate (DMSP) and dimethyl sulfide (DMS) are transferred and transformed in the food web and are affected by zooplankton, phytoplankton, and bacteria. This study investigated spatial distributions of DMS, DMSP, DMSP lyase activity (DLA), the abundances of bacteria, DMSP‐consuming bacteria, and dimethyl sulfoxide‐consuming bacteria in the surface seawater of the Bohai Sea and Yellow Sea. As results, the distributions of DMS and dissolved DMSP were significantly correlated with DLA. A deck incubation experiment indicated that grazing by microzooplankton promoted the conversion of DMSP to DMS and that mesozooplankton copepod grazing stimulated DMS production. These results provide a more comprehensive way to understand the possible DMS release mechanisms via zooplankton grazing. Key Points: Dimethyl sulfide (DMS) concentration was significantly correlated with dimethyl sulfoxide‐consuming bacterial abundanceMicrozooplankton grazing consumed 4%–7% of the total dimethylsulfoniopropionate daily and 16%–62% was converted to DMSCopepod ingestion stimulated DMS production, which increased by 299% at 48 hr in physically broken algal cells [ABSTRACT FROM AUTHOR]

Protozoa play a pivotal role in the microbial cycle, and ciliated protozoan grazing habits are associated with dimethyl sulfide (DMS) cycle. Many studies have explored the impacts of nanoplastics (NPs) and microplastics (MPs) on ecotoxicological effects of ciliates. However, limited research exists on NPs and MPs influences on the production of organic sulfur compounds. The impact of NPs and MPs on the production of dimethyl sulfoxide (DMSO) and carbonyl sulfide (COS) remains unclear. Therefore, we examined the impacts of three concentrations (1 × 105, 5 × 105, and 1 × 106 items/mL) of polystyrene (PS) NPs (50 nm) and MPs (1 and 5 μm) on the ecotoxicology and DMS/dimethylsulfoniopropionate (DMSP)/DMSO/COS production in the ciliate Uronema marinum. NPs and MPs exposure were found to reduce the abundance, growth rate, volume, and biomass of U. marinum. Additionally, NPs and MPs increased the superoxide anion radical (O 2 ˙─) production rates and malondialdehyde (MDA) contents (24 h), leading to a decline in glutathione (GSH) content and an ascend in superoxide dismutase (SOD) activity to mitigate the effects of reactive oxygen species (ROS). Exposure to PS NPs and MPs decreased the ingestion rates of algae by 7.5–14.4%, resulting in decreases in DMS production by 56.8–85.4%, with no significant impact on DMSO production. The results suggest a distinct pathway for the production of DMSO or COS compared to DMS. These findings help us to understand the NPs and MPs impacts on the marine ecosystem and organic sulfur compound yield, potentially influencing the global climate. [Display omitted] • Nano- and micro-plastics inhibited ciliate abundance and dimethyl sulfide yield. • O 2 ˙─ production rate and superoxide dismutase activity increased under NPs/MPs. • Dimethyl sulfoxide production was not affected by nano- and micro-plastics. [ABSTRACT FROM AUTHOR]

Dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP) are important sulfur compounds influenced by community assemblages of plankton. The distributions of DMS, DMSP, DMSP lyase activity (DLA), DMSP-consuming bacteria (DCB), and community structures of phytoplankton and zooplankton were investigated during summer in the Bohai Sea and Yellow Sea. The variety ranges of DMS, dissolved DMSP (DMSP d ), and particulate DMSP (DMSP p ) concentrations in the surface seawater were 1.46-28.52, 5.26-30.21, and 0.91-112.43 nmol/L, with averages of 6.64, 14.27, and 37.53 nmol/L, respectively. The maximum DMS and DMSP p concentrations appeared at stations H26 and H25 situated northeast of the Yangtze estuary, respectively. These maximum values maybe due to the enriched nutrients brought by the Yangtze River Diluted Water. Significantly positive correlations were observed between the DMS/DMSP p concentrations/DLA and chlorophyll a (Chl a) concentration. Additionally, the phytoplankton abundances were markedly positively correlated with DMS concentrations and DLA. DCB abundances showed a significant positive correlation with DMSP d concentrations. These findings indicated that phytoplankton and bacterial communities significantly influenced the DMS and DMSP d distributions. Furthermore, microzooplankton grazing was demonstrated promote the total DMSP (DMSP t ) turnover. These results elucidate the planktonic community assemblage roles in regulating the distributions of DMSP and DMS, contributing valuable insights into the biogeochemical cycle of organic sulfur compounds., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The outbreak of Ulva prolifera blooms causes significant changes in the coastal sulfur cycle due to the high production of dimethylsulfoniopropionate (DMSP) and the emission of dimethylsulfide (DMS). However, the sulfur metabolism mechanism of U. prolifera has not been thoroughly investigated. In this study, we examined the levels of intracellular and extracellular sulfate (SO 4 2- -S), total sulfur (TS), DMSP, and DMS in fresh U. prolifera under different light intensity conditions (54, 108 and 162 μmol photons m -2 s -1 ) during algal growth. We also conducted transcriptome analyses to investigate sulfur uptake and metabolism. When the light intensity increased by 50% (from 108 to 162 μmol photons m -2 s -1 ), the amount of absorbed SO 4 2- -S increased by 3.5 times after 24 h, while the fresh weight of U. prolifera increased by 16%, and the average release rates of DMS and DMSP increased by 136% and 100%, respectively. However, the expression of sulfate transporter and assimilation-related genes did not show significant up- or down-regulation in response to the light intensity changes. Therefore, it is speculated that the key gene responsible for DMSP synthesis in U. prolifera has not yet been identified. The sulfate metabolic pathway of U. prolifera was established, and four Alma genes, including DMSP lyase, were identified. During the bloom period, it is estimated that U. prolifera releases a maximum of approximately 0.4 tons of sulfur and 0.3 tons of carbon in the form of DMS into the atmosphere per day. Additionally, biogenic sulfur dissolved in seawater or within algae could potentially impact the regional climate and environment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

ABSTRACT Dimethylsulfoniopropionate (DMSP) is an abundant organic compound in marine surface water and source of dimethyl sulfide (DMS), the largest natural sulfur source to the upper atmosphere. Marine bacteria either mineralize DMSP through the demethylation pathway or transform it to DMS through the cleavage pathway. Factors that regulate which pathway is utilized are not fully understood. In chemostat experiments, the marine Roseobacter Ruegeria pomeroyi DSS-3 was exposed to oxidative stress either during growth with H2O2 or by mutation of the gene encoding catalase. Oxidative stress reduced expression of the genes in the demethylation pathway and increased expression of those encoding the cleavage pathway. These results are contrary to the sulfur demand hypothesis, which theorizes that DMSP metabolism is driven by sulfur requirements of bacterial cells. Instead, we find strong evidence consistent with oxidative stress control over the switch in DMSP metabolism from demethylation to DMS production in an ecologically relevant marine bacterium. IMPORTANCE Dimethylsulfoniopropionate (DMSP) is the most abundant low-molecular-weight organic compound in marine surface water and source of dimethyl sulfide (DMS), a climatically active gas that connects the marine and terrestrial sulfur cycles. Marine bacteria are the major DMSP consumers, either generating DMS or consuming DMSP as a source of reduced carbon and sulfur. However, the factors regulating the DMSP catabolism in bacteria are not well understood. Marine bacteria are also exposed to oxidative stress. RNA sequencing (RNA-seq) experiments showed that oxidative stress induced in the laboratory reduced expression of the genes encoding the consumption of DMSP via the demethylation pathway and increased the expression of genes encoding DMS production via the cleavage pathway in the marine bacterium Ruegeria pomeroyi. These results support a model where DMS production in the ocean is regulated in part by oxidative stress.

The copious compatible solute dimethylsulfoniopropionate (DMSP) plays significant roles in marine ecosystems. The DMSP degradation pathways in strain Alcaligenes faecalis M3A have been comprehensively studied, in which DMSP was cleaved into dimethyl sulphide (DMS) and acrylate. However, the transcriptional regulatory mechanism of DMSP degradation is not fully elucidated. In this study, the TetR/AcrR family transcriptional regulator DdaR repressing acuI operon in strain M3A was investigated. The transcription start sites and promoters of the acuI and ddaR operons was identified. DdaR bound to both the acuI and ddaR promoter regions in EMSA experiment. Two binding sites of DdaR shared conserved motif 5′-CNNCGTNACGNNG-3′ which was essential for the DdaR binding. DdaR was inhibited from binding to the acuI promoter region by acrylate, which acted as a ligand of DdaR. Site-directed mutagenesis was used to investigate the impact of four key amino acid residues (Y61, K67, E135, and I169) in DdaR, revealing their essential roles in the functioning of DdaR. The findings of this study unveil a negative transcriptional regulation mechanism of DMSP degradation in A. faecalis M3A by DdaR and provide a new understanding of the TetR/AcrR-type transcriptional regulators. • The DdaR-binding region in acuI and ddaR operons' promoter were identified. • The transcription start site and promoter of the acuI and ddaR operons were identified. • Acrylate acting as the possible substrates for DdaR. • The role of four key amino acid residues of DdaR were identified. [ABSTRACT FROM AUTHOR]

Dimethylsulfoniopropionate (DMSP) is a ubiquitous organosulfur molecule in marine environments with important roles in stress tolerance, global carbon and sulfur cycling, and chemotaxis. It is the main precursor of the climate active gas dimethyl sulfide (DMS), which is the greatest natural source of bio‑sulfur transferred from ocean to atmosphere. Alteromonas sp. M12, a Gram-negative and aerobic bacterium, was isolated from the seawater samples collected from the Mariana Trench at the depth of 2500 m. Here, we report the complete genome sequence of strain M12 and its genomic characteristics to import and utilize DMSP. The genome of strain M12 contains one circular chromosome (5,012,782 bp) with the GC content of 40.88%. Alteromonas sp. M12 can grow with DMSP as a sole carbon source, and produced DMS with DMSP as a precursor. Genomic analysis showed that strain M12 contained a set of genes involved in the downstream steps of DMSP cleavage, but no known genes encoding DMSP transporters or DMSP lyases. The results indicated that this strain contained novel DMSP transport and cleavage genes in its genome which warrants further investigation. The import of DMSP into cells may be a strategy of strain M12 to adapt the hydrostatic pressure environment in the Mariana Trench, as DMSP can be used as a hydrostatic pressure protectant. This study sheds light on the catabolism of DMSP by deep-sea bacteria. [ABSTRACT FROM AUTHOR]

Dimethylsulfoniopropionate (DMSP) and dimethyl sulfide (DMS) are critical molecules in the global sulfur cycle and in climate regulation. Bacterial DMSP-dependent DMS production is an important natural source of DMS. The aim of the present work was to use RNA-seq technology to investigate the changes in gene expression profiles of Antarctic Rhodococcus sp. NJ-530 in response to DMSP, and the possible mechanism of DMSP metabolism. In this study, Rhodococcus sp. NJ-530 cells were exposed to 0 (control) and 1 mM DMSP for 9 h. The results showed that DMSP induces transcriptional changes to Rhodococcus sp. NJ-530. DMSP caused upregulation of several genes that may play a potential role in DMSP metabolization. Additionally, transcriptome analysis of DMSP metabolism determinized a total of 1159 differentially expressed genes (DEGs) between two treatment strategies. qRT-PCR was performed to further confirm the changes in these results. GO and KEGG enrichment analyses showed that DMS production is the result of the coordinated action of a multitude of DMSP lysis-associated genes along a pathway, including absorption mechanism, secondary metabolisms, and cellular signaling. In conclusion, our data indicated that DMSP exposure induced DMSP cleavage pathway activity, and the effects on the gene expression profile of strain NJ-530 were analyzed at the transcriptional level during the degradation of DMSP. This work provided insight into the transcriptional characterization of Rhodococcus sp. NJ-530 in response to DMSP and contributed to clarifying the biodegradation and underlying mechanism of DMSP in Rhodococcus sp. NJ-530. [ABSTRACT FROM AUTHOR]

The coastal ecosystems are highly sensitive to climate change and are usually influenced by variations in phytoplankton communities and water physiochemical factors. In the present study, the phytoplankton community, chlorophyll a (Chl a) and their relationships with environmental variables and dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) were investigated in spring 2017 (March 24 to April 16) in the East China Sea (26.0°–33.0°N, 120.0°–128.0°E) and southern Yellow Sea (31.0°–36.0°N, 120.0°–125.0°E). The spatial distributions of phytoplankton species composition and cell density were investigated by qualitative and quantitative methods and were compared with historical data to study phytoplankton species succession in the survey area. The results showed that there were 275 phytoplankton species belonging to 90 genera and 6 phyla in the survey area, of which 208 species belonged to 62 genera of Bacillariophyta and 56 species belonged to 20 genera of Pyrrophyta. The dominant phytoplankton species were Skeletonema dohrnii, Chaetoceros vanheurckii and Prorocentrum donghaiense. The phytoplankton cell densities ranged from 0.06×104 cells/L to 418.73×104 cells/L, with an average value of 21.46×104 cells/L. In spring, the average ratio of Bacillariophyta/Pyrrophyta was 41.13 for the entire study area. The areas with high phytoplankton cell density were mainly distributed in the northern South Yellow Sea and offshore waters of the East China Sea. According to a canonical correspondence analysis among phytoplankton and environmental parameters, the water Chl a concentrations were notably consistent with phytoplankton cell density (P<0.001), and both showed significant negative correlations with salinity and nitrite (P<0.05) and significant positive correlations with dissolved oxygen and pH (P<0.001). There was a significant positive correlation between diatom (both in cell density and in dominant species) and DMS (P<0.05), which indicated that diatoms play a greater role in DMS production in this investigated area. [ABSTRACT FROM AUTHOR]

Continuous input from the Changjiang River significantly reshuffled the ecosystems in the Changjiang Estuary and adjacent East China Sea, impacting the production, distribution, and emission of marine dimethyl sulfide (DMS). However, the effect of phytoplankton biomass and composition on DMS under different nutrient inputs remains poorly understood. Two comprehensive cruises to characterize their effects were conducted in spring and summer 2015. The areas with high concentrations of DMS, dimethylsulfoniopropionate (precursor of DMS), and dimethyl sulfoxide (photo‐oxidation product of DMS) were largely consistent with high phytoplankton abundances along the front of Changjiang Diluted Water in both seasons. Both the higher conversion ratio of dissolved dimethylsulfoniopropionate to DMS and the higher DMS biological production rate in summer contributed to the higher DMS levels. Once produced in seawater, more than half of the DMS was directly consumed by microbes, resulting in a turnover time of 1–2 days, which was shorter than that driven by ventilation. A ship‐based incubation experiment revealed that, with increasing N/Si and N/P ratios from the Changjiang River, phytoplankton biomass increased and the community shifted from diatom‐dominated to dinoflagellate‐dominated, which was conducive to DMS production. It was noteworthy that strong DMS photo‐degradation induced by high nitrate concentrations may have masked DMS production to some extent, while urea only had a promoting effect and therefore led to a maximum increase in DMS yield. Our findings indicated that the increase in phytoplankton biomass and succession of phytoplankton community induced by changes in nutrient inputs will promote DMS emissions from the Changjiang Estuary. Plain Language Summary: The Changjiang River is the third‐longest river in the world. It persistently discharges a large number of terrestrial materials into the Changjiang Estuary and adjacent seas and therefore results in a major reshuffling of marine ecosystems, inevitably affecting the production, distribution, and emission of marine dimethyl sulfide (DMS). DMS is the largest biogenic sulfur source for the atmosphere and plays a critical role in climate feedback. Therefore, a systematic investigation was conducted in relevant waters to study the effects of different nutrient inputs from the Changjiang River on the production and emission of estuarine DMS. Abundant nutrients imported from the Changjiang Diluted Water have promoted phytoplankton growth and subsequent DMS production. Besides, with the increasing ratios of N/Si and N/P in nutrients, the community succession shifting from diatoms (inefficient producer of DMS) to dinoflagellates (prolific producers of DMS) have further enhanced DMS production. It was noteworthy that strong DMS photo‐degradation induced by high nitrate concentration may mask DMS production to some extent, while urea only has a promoting effect and therefore led to a maximum increase in DMS yield. The resulting increases in DMS concentrations will promote DMS emissions and consequently play a non‐negligible role in regional climate regulation. Key Points: Frequent algal blooms led to drastic fluctuations in the concentrations and sea‐to‐air fluxes of dimethyl sulfideIncreasing trends of nutrient loads from the Changjiang River will enhance estuarine dimethyl sulfide productionIn seawater, urea caused larger increases in the concentrations of dimethyl sulfide than nitrate [ABSTRACT FROM AUTHOR]

The acyl-coenzyme A (CoA) dehydrogenase family enzyme DmdC catalyzes the third step in the dimethylsulfoniopropionate (DMSP) demethylation pathway, the oxidation of 3-methylmercaptopropionyl-CoA (MMPA-CoA) to 3-methylthioacryloyl-CoA (MTA-CoA). To study its substrate specificity, the recombinant DmdC1 from Ruegeria pomeroyi was characterized. In addition to MMPA-CoA, the enzyme was highly active with short-chain acyl-CoAs, with Km values for MMPA-CoA, butyryl-CoA, valeryl-CoA, caproyl-CoA, heptanoyl-CoA, caprylyl-CoA, and isobutyryl-CoA of 36, 19, 7, 11, 14, 10, and 149 μM, respectively, and kcat values of 1.48, 0.40, 0.48, 0.73, 0.46, 0.23, and 0.01 s-1, respectively. Among these compounds, MMPA-CoA was the best substrate. The high affinity of DmdC1 for its substrate supports the model for kinetic regulation of the demethylation pathway. In contrast to DmdB, which catalyzes the formation of MMPA-CoA from MMPA, CoA, and ATP, DmdC1 was not affected by physiological concentrations of potential effectors, such as DMSP, MMPA, ATP, and ADP. Thus, compared to the other enzymes of the DMSP demethylation pathway, DmdC1 has only minimal adaptations for DMSP metabolism compared to other enzymes in the same family with similar substrates, supporting the hypothesis that it evolved relatively recently from a short-chain acyl-CoA dehydrogenase involved in fatty acid oxidation. IMPORTANCE We report the kinetic properties of DmdC1 from the model organism R. pomeroyi and close an important gap in the literature. While the crystal structure of this enzyme was recently solved and its mechanism of action described (X. Shao, H. Y. Cao, F. Zhao, M. Peng, et al., Mol Microbiol 111:1057-1073, 2019, https://doi.org/10 .1111/mmi.14211), its substrate specificity and sensitivity to potential effectors was never examined. We show that DmdC1 has a high affinity for other short-chain acylCoAs in addition to MMPA-CoA, which is the natural substrate in DMSP metabolism and is not affected by the potential effectors tested. This evidence supports the hypothesis that DmdC1 possesses few adaptations to DMSP metabolism and likely evolved relatively recently from a short-chain acyl-CoA dehydrogenase involved in fatty acid oxidation. This work is important because it expands our understanding of the adaptation of marine bacteria to the increased availability of DMSP about 250 million years ago. [ABSTRACT FROM AUTHOR]

The fate of dimethylsulfoniopropionate (DMSP), the precursor of the climatologically important gas dimethylsulfide (DMS), depends on the structure of marine communities. DMSP degradation by DMSP‐consuming bacteria (DCB) is an important sink of dissolved DMSP (DMSPd) in seawater. DMSP cleavage and demethylation are two DMSPd consumption pathways, and the DMSPd cleavage pathway involves DMSP lyase activity (DLA). Here, we studied the distribution of DMS, DMSP, DCB, and DLA in the seawater of the Yellow Sea and East China Sea in the summer of 2013 and the degradation of DMSPd by DCB. High DCB abundances, as well as DMS and dissolved, particulate, total DMSP (DMSPd,p,t) concentrations were observed near the Hongzhou Bay, which may be due to the high productivity of dinoflagellates. The spatial distribution of DCB abundance was most likely the result of the regional hydrography including upwelling near Hangzhou Bay and the discharge of Yangtze Diluted Water (YDW). The DLA along the YDW decreased from coastal water to open sea. The DMSPd consumption by DCB Bacillus sp. YES023 isolated from the seawater was accompanied by DMS production (≤8.2% of DMSPd consumption). Bacillus sp. YES023 could also grow using glycine betaine, acrylic acid, dimethylsulfoxide, monomethylamine, or dimethylamine as a sole carbon source. Glycine betaine and acrylic acid were the most favorable substrates for overall growth. These results help our understanding of bacterial catabolism and the degradation pathways of methyl sulfur compounds in the ocean. Plain Language Summary: Bacterial catabolism of dissolved dimethylsulfoniopropionate (DMSP) (DMSPd) is an important sink of DMSP in seawater. There are two DMSPd consumption pathways (DMSP cleavage and demethylation), and the dimethylsulfide (DMS)‐producing (DMSP cleavage) pathway involves DMSP lyase activity (DLA). In this study, we evaluated the DMS, DMSP, DMSP‐consuming bacteria (DCB) abundance, and DLA distributions in the seawater of the Yellow Sea and East China Sea. DCB in the seawater were isolated and identified. The degradation of DMSPd by and the bioavailability of the other five organic carbon analog of DMSP (including glycine betaine, acrylic acid, dimethylsulfoxide, monomethylamine, and dimethylamine) to DCB Bacillus sp. YES023 were investigated. Key Points: Dimethylsulfoniopropionate (DMSP)‐consuming bacteria abundance and DMSP lyase activity were evaluatedDMSP consumption by Bacillus sp. YES023 was accompanied by dimethylsulfide production (≤8.2%)Glycine betaine and acrylic acid were more favorable as substrates for the growth of Bacillus sp. YES023 than DMSP [ABSTRACT FROM AUTHOR]

The present work aims at determining the natural variability of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) contents in the seagrass Posidonia oceanica, which is the largest producer of these molecules reported to date among coastal autotrophs. Seagrass leaf samples were collected during a period of 3.5 years in the pristine Revellata Bay (Calvi, northwestern Corsica, France). The DMSP content ranged from 25 to 265 µmol.gfw−1; DMSO from 1.0 to 13.9 µmol.gfw−1. The dynamics of the two molecules were closely linked, the DMSO content being equivalent to 3.5% of the DMSP content, all leaf samples considered (n = 423 samples and 414 DMSP(O) data pairs). The annual growth cycle of the seagrass diluted the initial stocks of the two molecules. Temperature indirectly affected molecule content dynamics through their direct effect on the seagrass productivity and biomass. Inter-annual variations in DMSP(O) content in relation to shallow water temperature might further indicate that DMSP(O) could have been involved in the physiological response of P. oceanica to heat stress. Finally, middle-aged leaf tissues with an organosulfur molecule content similar to the average value calculated for the seagrass leaf bundle appeared to be the best choice of sample material to study DMSP and DMSO in that species. More research is needed to elucidate the biosynthetic pathways of these molecules in seagrasses, the evolutionary reasons for such a high production in P. oceanica and the physiological functions they play. [ABSTRACT FROM AUTHOR]

Environmental context: Dimethyl sulfide is an important biogenic gas, released from ocean to atmosphere, which contributes to aerosol formation and can therefore affect global climate. Studies on dimethyl sulfide in both seawater and atmosphere have linked the atmospheric chemistry of dimethyl sulfide with its circulation in the marine environment. This study showed that these biogenic emissions contribute to the sulfur cycle and particulate production, deepening our understanding of their role in the East China Sea. Dimethyl sulfide (DMS) is identified as an essential biogenic sulfur compound in the ocean. Its oxidation products are thought to be important contributors to cloud condensation nuclei, thereby influencing the earth's radiative balance and climate. The concentrations of DMS and its precursor, dimethylsulfoniopropionate (DMSP) were measured in seawater and sediment pore water in the East China Sea (ECS) during summer. In addition, dissolved DMSP (DMSPd) degradation rates, DMS production and consumption rates, and sea-to-air flux of DMS were determined, and the biogenic contribution to atmospheric non-sea-salt sulfate (nss-SO42-) was evaluated in PM2.5 and PM10 aerosols over the study area. The spatial distributions of DMS and DMSP were closely related to that of chlorophyll-a and decreased from the inshore to the offshore. The concentration of DMSPd in sediment pore water was significantly higher than that in bottom water, which indicated that sediment is a net source of DMSPd for bottom water. The biological incubation experiments showed that ~36.0 % of decomposed DMSPd was degraded into DMS, while 78.7 % of produced DMS was consumed by bacteria within the surface water. The sea-to-air flux of DMS varied from 1.30 to 31.84 μmol m-2 day-1, with an average of 7.45 ± 6.30 μmol m-2 day-1. Biogenic contributions of the ECS to total nss-SO42- were estimated to be 13.0 % ± 9.9 % in PM2.5 and 13.5 % ± 5.1 % in PM10 samples respectively, which indicated that marine DMS release cannot be neglected in the ECS during summer. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD), the most common neurodegenerative disorder, affects a broad spectrum of aging populations. AD is characterized by pathological amyloid-β (Aβ) plaques and neurofibrillary tangles, leading to neural degeneration and cognitive decline. The lack of effective treatments for AD highlights the urgent need for novel therapeutic agents, particularly in the early stages. Dimethylsulfoniopropionate (DMSP) is a natural marine compound with antioxidant and neuroprotective properties. However, studies on the efficacy of DMSP in the treatment of AD and its associated mechanisms are limited. This study aimed to explore the therapeutic effects and mechanisms of action of DMSP as an AD treatment using a preclinical 3 × Tg-AD mouse model. The research involved administering DMSP (7 μg/mL and 11 μg/mL in drinking water) to four-month-old 3 × Tg-AD mice consecutively for three months. The Y-maze test, novel object recognition test, and Morris water maze test were used to assess memory and learning ability. The relative expression levels and distribution of proteins relevant to Aβ and tau pathology, synapses, and glial cells were analyzed using western blotting and immunofluorescence assays. Additionally, proteomic and bioinformatics approaches were used to explore the potential targets of DMSP treatment. DMSP-treated AD mice showed significantly enhanced cognitive function, suggesting that DMSP mitigates memory and learning impairments in AD. Moreover, DMSP diminished the abnormal accumulation of Aβ and phosphorylated tau in both the cortex and hippocampus, which are crucial hallmarks of AD pathology. In addition to its neuroprotective properties, DMSP restored synaptic density and the expression of synaptic and neuronal proteins, which are essential for proper brain function. DMSP displayed anti-inflammatory properties, as evidenced by its ability to suppress inflammatory astrocytes and maintain microglial homeostasis. Notably, DMSP facilitated the maturation of oligodendrocytes (OLs) from oligodendrocyte progenitor cells (OPCs), a critical process in the development of the brain myelination architecture. Proteomic analysis revealed that DMSP positively influenced biological processes crucial for oligodendrocyte development, myelination, and axonal ensheathment, which are often compromised in patients with AD. Protein validation and brain tissue staining supported the role of DMSP in preserving myelin enrichment and sheath integrity. These therapeutic effects were largely attributed to the enhanced expression of myelin-associated glycoprotein (Mag) and tetraspanin Cd9. Overall, our findings highlight DMSP as a promising novel therapeutic candidate for AD, offering multifaceted benefits in cognitive and memory enhancement, reduction of Aβ and tau pathology, neuronal synapse protection, anti-inflammatory effects, and myelin sheath restoration as an innovative target compared to other studies. In addition to being a potentially effective treatment for AD, DMSP may also have the potential to address other neurodegenerative diseases that are closely associated with myelin impairment. [ABSTRACT FROM AUTHOR]

Due to the potential impacts of microplastics (MPs) and nanoplastics (NPs) on algal growth and thereby affect the climate-relevant substances, dimethylsulfoniopropionate (DMSP) and dimethyl sulfide (DMS), we studied the polystyrene (PS) MPs and NPs of 1 μm and 80 nm impacts on the growth, chlorophyll content, reactive oxygen species (ROS), antioxidant enzyme activity, and DMS/DMSP production in Emiliania huxleyi. E. huxleyi is a prominent oceanic alga that plays a key role in DMS and DMSP production. The results revealed that high concentrations of MPs and NPs inhibited the growth, carotenoid (Car), and Chl a concentrations of E. huxleyi. However, short-time exposure to low concentrations of PS MPs and NPs stimulated the growth of E. huxleyi. Furthermore, high concentrations of MPs and NPs resulted in an increase in the superoxide anion radical (O 2 . –) production rate and a decrease in the malondialdehyde (MDA) content compared with the low concentrations. Exposure to MPs and NPs at 5 mg L−1 induced superoxide dismutase (SOD) activity as a response to scavenging ROS. High concentrations of MPs and NPs significantly inhibited the production of DMSP and DMS. The findings of this study support the potential ecotoxicological impacts of MPs and NPs on algal growth, antioxidant system, and dimethylated sulfur compounds production, which maybe potentially impact the global climate. [Display omitted] • High concentration polystyrene micro- and nanoplastics inhibited E. huxleyi growth. • Short time/low concentration micro- and nanoplastics stimulated E. huxleyi growth. • High concentration micro- and nanoplastics increased O 2 .- production rate. • High concentration micro- and nanoplastics inhibited dimethyl sulfide production. [ABSTRACT FROM AUTHOR]

Dimethylsulfoniopropionate (DMSP) is one of the most abundant sulfur-containing organic compounds on the earth, which is an important carbon and sulfur source and plays an important role in the global sulfur cycle. Marine microorganisms are an important group involved in DMSP metabolism. The strain Cobetia sp. D5 was isolated from seawater samples in the Yellow Sea area of Qingdao during an algal bloom. There is still limited knowledge on the capacity of DMSP utilization of Cobetia bacteria. The study reports the whole genome sequence of Cobetia sp. D5 to understand its DMSP metabolism pathway. The genome of Cobetia sp. D5 consists of a circular chromosome with a length of 4,233,985 bp and the GC content is 62.56%. Genomic analysis showed that Cobetia sp. D5 contains a set of genes to transport and metabolize DMSP, which can cleave DMSP to produce dimethyl sulphide (DMS) and 3-Hydroxypropionyl-Coenzyme A (3-HP-CoA). DMS diffuses into the environment to enter the global sulfur cycle, whereas 3-HP-CoA is catabolized to acetyl CoA to enter central carbon metabolism. Thus, this study provides genetic insights into the DMSP metabolic processes of Cobetia sp. D5 during a marine algal bloom, and contributes to the understanding of the important role played by marine bacteria in the global sulfur cycle. [ABSTRACT FROM AUTHOR]

Marine distribution of dimethylsulfoniopropionate (DMSP) and its cleavage product dimethyl sulfide (DMS) is greatly affected by the community structures of bacteria, phytoplankton, and zooplankton. Spatial distributions of dissolved and particulate DMSP (DMSP d,p), and DMS were measured and their relationships with DMSP lyase activity (DLA), abundance of DMSP-consuming bacteria (DCB), and the community structures of phytoplankton, zooplankton, and bacteria were determined during summer in the South China Sea (SCS). The depth distributions of DMSP d,p exhibited a similar trend with Chl a , reaching their maxima in the mixing layer. The DMS concentration was positively correlated with DCB abundance and DLA, indicating that DCB and DMSP lyase had a significant effect on DMS production. High DMS concentrations in the horizontal distribution coincided with high DCB abundance and DLA and may be due to the rapid growth of phytoplankton resulting from the high dissolved inorganic nitrogen concentration brought by the cold vortices. Moreover, the highest copepod abundance at station G3 coincided with the highest DMS concentrations there among stations B4, F2, and G3. These results suggest that copepod may play an important role in DMS production. The bacterial SAR11 clade was positively correlated with DLA, indicating its significant contribution to DMSP degradation in the SCS. These findings contribute to the understanding of the effect of the community assemblage on DMSP/DMS distributions in the SCS dominated by mesoscale vortices. [Display omitted] • Mesoscale vortex drove DMS/DMSP distributions in the South China Sea. • DMS depth distributions coincided with DMSP-consuming bacterial distributions. • High DMSP p concentrations occurred at 75 m due to high Chl a concentration there. • Bacteria SAR11 clade contributed significantly to the DMSP degradation. [ABSTRACT FROM AUTHOR]

Strain HIMB11 is a planktonic marine bacterium isolated from coastal seawater in Kaneohe Bay, Oahu, Hawaii belonging to the ubiquitous and versatile Roseobacter clade of the alphaproteobacterial family Rhodobacteraceae. Here we describe the preliminary characteristics of strain HIMB11, including annotation of the draft genome sequence and comparative genomic analysis with other members of the Roseobacter lineage. The 3,098,747 bp draft genome is arranged in 34 contigs and contains 3,183 protein- coding genes and 54 RNA genes. Phylogenomic and 16S rRNA gene analyses indicate that HIMB11 represents a unique sublineage within the Roseobacter clade. Comparison with other publicly available genome sequences from members of the Roseobacter lineage reveals that strain HIMB11 has the genomic potential to utilize a wide variety of energy sources (e.g. organic matter, reduced inorganic sulfur, light, carbon monoxide), while possessing a reduced number of substrate transporters.

Dimethylsulfoniopropionate (DMSP), a key component of the global geochemical sulfur cycle, is a secondary metabolite produced in large quantities by marine phytoplankton and utilized as an osmoprotectant, thermoprotectant, and antioxidant. Marine bacteria can use two pathways to degrade and catabolize DMSP, a demethylation pathway and a cleavage pathway that produces the climate-active gas dimethylsulfide (DMS). Whether marine bacteria can also accumulate DMSP as an osmoprotectant to maintain the turgor pressure of the cell in response to changes in external osmolarity has received little attention. The marine halophile Vibrio parahaemolyticus contains at least six osmolyte transporters, namely four betaine carnitine choline transport (BCCT) carriers (BccT1 to BccT4) and two ATP-binding cassette (ABC) family ProU transporters. In this study, we showed that DMSP is used as an osmoprotectant by V. parahaemolyticus and by several other Vibrio species, including Vibrio cholerae and Vibrio vulnificus. Using a V. parahaemolyticus proU double mutant, we demonstrated that these ABC transporters are not required for DMSP uptake. However, a bccT null mutant lacking all four BCCTs had a growth defect compared to the wild type (WT) in high-salinity medium supplemented with DMSP. Using mutants possessing only one functional BCCT in growth pattern assays, we identified two BCCT family transporters, BccT1 and BccT2, that are carriers of DMSP. The only V. parahaemolyticus BccT homolog that V. cholerae and V. vulnificus possess is BccT3, and functional complementation in Escherichia coli MKH13 showed that V. cholerae VcBccT3 could transport DMSP. In V. vulnificus strains, we identified and characterized an additional BCCT family transporter, which we named BccT5, that was also a carrier for DMSP. [ABSTRACT FROM AUTHOR]

Dimethyl sulfide (DMS) is an important component of the global sulfur cycle as it is the most abundant sulfur compound that is emitted via the ocean surface to the atmosphere. Dimethylsulfoniopropionate (DMSP), the precursor of DMS, is mainly produced by phytoplankton and is degraded by marine bacteria. To reveal the role of bacteria in the regulation of DMSP degradation and DMS production, mesocosm and field studies were performed in the Sanriku Coast on the Pacific Ocean in northeast Japan. The responsible bacteria for the transformation of DMSP to DMS and the assimilation of DMSP were monitored, and the genes encoding DMSP lyase (dddD and dddP) and DMSP demethylase (dmdA) were analyzed. The mesocosm study showed that the dmdA subclade D was the dominant DMSP degradation gene in the free-living (FL) and particle-associated (PA) fractions. The dddD gene was found in higher abundance than the dddP gene in all the tested samples. Most importantly, DMS concentration was positively correlated with the abundance of the dddD gene. These results indicated that bacteria possessing dmdA and dddD genes were the major contributors to the DMSP degradation and DMS production, respectively. The genes dmdA subclade D and dddP were abundant in the Tsugaru Warm (TW) Current, while the dmdA subclade C/2 and dddD genes were dominant in the Oyashio (OY) Current. Functional gene network analysis also showed that the DMSP degradation genes were divided into OY and TW Current-related modules, and genes sharing similar functions were clustered in the same module. Our data suggest that environmental fluctuations resulted in habitat filtering and niche partitioning of bacteria possessing DMSP degradation genes. Overall, our findings provide novel insights into the distribution and abundance of DMSP degradation genes in a coastal region with different water current systems.

Abstract The marine sulfur cycle is substantially fueled by the phytoplankton osmolyte dimethylsulfoniopropionate (DMSP). This metabolite can be metabolized by bacteria, which results in the emission of the volatile sulfur species methanethiol (MeSH) and the climate‐cooling dimethylsulfide (DMS). It is generally accepted that bacteria contribute significantly to DMSP turnover. We show that the other low molecular weight zwitterionic dimethylsulfonio compounds dimethylsulfonioacetate (DMSA) and gonyol are also widely distributed in phytoplankton and can serve as alternative substrates for volatile production. DMSA was found in 11 of the 16 surveyed phytoplankton species, and gonyol was detected in all haptophytes and dinoflagellates. These prevalent zwitterions are also metabolized by marine bacteria. The patterns of bacterial MeSH and DMS release were dependent on the zwitterions present. Certain bacteria metabolize DMSA and gonyol and release MeSH, in others gonyol inhibited DMS‐producing enzymes. If added in addition to DMSP, gonyol entirely inhibited the formation of volatiles in Ruegeria pomeroyi. In contrast, no substantial effect of this compound was observed in the DMSP metabolism of Halomonas sp. We argue that the production of DMSA and gonyol and their inhibitory properties on the release of volatiles from DMSP has the potential to modulate planktonic sulfur cycling between species.

ABSTRACT Dimethylsulfoniopropionate (DMSP) is abundant in marine environments and an important source of reduced carbon and sulfur for marine bacteria. While both Ruegeria pomeroyi and Ruegeria lacuscaerulensis possessed genes encoding the DMSP demethylation and cleavage pathways, their responses to DMSP differed. A glucose-fed, chemostat culture of R. pomeroyi consumed 99% of the DMSP even when fed a high concentration of 5 mM. At the same time, cultures released 19% and 7.1% of the DMSP as dimethylsulfide (DMS) and methanethiol, respectively. Under the same conditions, R. lacuscaerulensis consumed only 28% of the DMSP and formed one-third of the amount of gases. To examine the pathways of sulfur and methyl C assimilation, glucose-fed chemostats of both species were fed 100 μM mixtures of unlabeled and doubly labeled [dimethyl-13C, 34S]DMSP. Both species derived nearly all of their sulfur from DMSP despite high sulfate availability. In addition, only 33% and 50% of the methionine was biosynthesized from the direct capture of methanethiol in R. pomeroyi and R. lacuscaerulensis, respectively. The remaining methionine was biosynthesized by the random assembly of free sulfide and methyl-tetrahydrofolate derived from DMSP. Thus, although the two species possessed similar genes encoding DMSP metabolism, their growth responses were very different. IMPORTANCE Dimethylsulfoniopropionate (DMSP) is abundant in marine environments and an important source of reduced carbon and sulfur for marine bacteria. DMSP is the precursor for the majority of atmospheric dimethylsulfide (DMS), a climatically active gas that connects the marine and terrestrial sulfur cycles. Although research into the assimilation of DMSP has been conducted for over 20 years, the fate of DMSP in microbial biomass is not well understood. In particular, the biosynthesis of methionine from DMSP has been a focal point, and it has been widely believed that most methionine was synthesized via the direct capture of methanethiol. Using an isotopic labeling strategy, we have demonstrated that the direct capture of methanethiol is not the primary pathway used for methionine biosynthesis in two Ruegeria species, a genus comprised primarily of globally abundant marine bacteria. Furthermore, although the catabolism of DMSP by these species varied greatly, the anabolic pathways were highly conserved.

Dimethylsulfoniopropionate (DMSP) is produced in surface seawater by phytoplankton. Phytoplankton culture experiments have shown that nanoeucaryotes (NANO) display much higher mean DMSP-to-Carbon or DMSP-to-Chlorophyll (Chl) ratios than Prochlorococcus (PRO), Synechococcus (SYN) or diatoms (DIAT). Moreover, the DMSP-lyase activity of algae which cleaves DMSP into dimethylsulfide (DMS) is even more group specific than DMSP itself. Ship-based observations have shown at limited spatial scales, that sea surface DMS-to-Chl ratios (DMS:Chl) are dependent on the composition of phytoplankton groups. Here we use satellite remote sensing of Chl (from SeaWiFS) and of Phytoplankton Group Dominance (PGD from PHYSAT) with ship-based sea surface DMS concentrations (8 cruises in total) to assess this dependence on an unprecedented spatial scale. PHYSAT provides PGD (either NANO, PRO, SYN, DIAT, Phaeocystis (PHAEO) or coccolithophores (COC)) in each satellite pixel (1/4° horizontal resolution). While there are identification errors in the PHYSAT method, it is important to note that these errors are lowest for NANO PGD which we typify by high DMSP:Chl. In summer, in the Indian sector of the Southern Ocean, we find that mean DMS:Chl associated with NANO + PHAEO and PRO + SYN + DIAT are 13.6±8.4 mmol g−1 (n=34) and 7.3±4.8 mmol g−1 (n=24), respectively. That is a statistically significant difference (P

Dimethylsulfoniopropionate (DMSP) is widespread in the oceans, and its biological metabolite, dimethyl sulfide (DMS), plays an important role in the atmosphere. The Antarctic region has become a hotspot in DMS studies due to the high spatial and temporal variability in DMS(P) concentration, but the level of bacterial DMS production remains unclear. In this study, a bacterium isolated from Antarctic floating ice, Rhodococcus sp. NJ‐530, was found to metabolize DMSP into DMS, and the rate of DMS production was measured as 3.96 pmol·mg protein−1·h−1. Rhodococcus sp. NJ‐530 had a DddD‐Rh enzyme containing two CaiB domains, which belonged to the CoA‐transferase III superfamily. However, the DddD‐Rh had a molecular weight of 73.21 kDa, which was very different from previously characterized DddD enzymes in sequence and evolution. In vitro assays showed that DddD‐Rh was functional in the presence of acetyl‐CoA. This was the first functional DddD from Gram‐positive Actinobacteria. Moreover, a quantitative real‐time polymerase chain reaction revealed that high temperature facilitated the expression of dddD‐Rh, and changes of salinity had little effect on it. This study adds new evidence to the bacterial DMS production in the Southern Ocean and provides a basis for investigating the metabolic mechanism of DMSP in extreme environments. [ABSTRACT FROM AUTHOR]

Phaeocystis antarctica is an important primary producer in the Southern Ocean and plays roles in sulfur cycles through intracellular production of dimethylsulfoniopropionate (DMSP), a principal precursor of dimethyl sulfide (DMS). Haptophytes, including P. antarctica, are known to produce more DMSP than other phytoplankton groups such as diatoms and green algae, suggesting their important contribution to DMS concentrations in the Southern Ocean. We assessed how sea ice formation and melting affect photosynthesis and DMSP accumulation in P. antarctica both in seawater and in sea ice. Incubations were undertaken in an ice tank, which simulated sea ice formation and melting dynamics. The maximum quantum yield of photochemistry (Fv/Fm) in photosystem II, as estimated from pulse‐amplitude‐modulated (PAM) fluorometry, was generally higher under low‐light conditions than high‐light conditions. Values of Fv/Fm, the relative maximum electron rate (rETRmax), and photosynthetic efficiency (α) were lower in sea ice than in seawater, implying reduced photosynthetic function inside the sea ice. The reduction in photosynthetic function was probably due to the hypersaline environment in the brine channels. Total DMSP (DMSPt) concentration normalized by chlorophyll‐a concentration was significantly higher in the sea ice than in the other environments, suggesting high accumulation of DMSP, probably due to its osmotic properties. Fv/Fm, specific growth rate, and DMSPt concentrations decreased with decreasing salinity with the lowest values found at a salinity of 22, that is, the lowest salinity tested. These results suggest that sea ice melting is responsible for a reduction in growth rate and DMSP production of P. antarctica. [ABSTRACT FROM AUTHOR]

Phaeocystis antarctica is an important primary producer in the Southern Ocean and plays roles in sulfur cycles through intracellular production of dimethylsulfoniopropionate (DMSP), a principal precursor of dimethyl sulfide (DMS). Haptophytes, including P. antarctica, are known to produce more DMSP than other phytoplankton groups such as diatoms and green algae, suggesting their important contribution to DMS concentrations in the Southern Ocean. We assessed how sea ice formation and melting affect photosynthesis and DMSP accumulation in P. antarctica both in seawater and in sea ice. Incubations were undertaken in an ice tank, which simulated sea ice formation and melting dynamics. The maximum quantum yield of photochemistry (Fv/Fm) in photosystem II, as estimated from pulse‐amplitude‐modulated (PAM) fluorometry, was generally higher under low‐light conditions than high‐light conditions. Values of Fv/Fm, the relative maximum electron rate (rETRmax), and photosynthetic efficiency (α) were lower in sea ice than in seawater, implying reduced photosynthetic function inside the sea ice. The reduction in photosynthetic function was probably due to the hypersaline environment in the brine channels. Total DMSP (DMSPt) concentration normalized by chlorophyll‐a concentration was significantly higher in the sea ice than in the other environments, suggesting high accumulation of DMSP, probably due to its osmotic properties. Fv/Fm, specific growth rate, and DMSPt concentrations decreased with decreasing salinity with the lowest values found at a salinity of 22, that is, the lowest salinity tested. These results suggest that sea ice melting is responsible for a reduction in growth rate and DMSP production of P. antarctica. [ABSTRACT FROM AUTHOR]

Summary: Dimethylsulfoniopropionate (DMSP) is a globally abundant marine metabolite and a significant source of organic carbon and sulfur for marine microbial ecosystems with the potential to influence climate regulation. However, the physiological function of DMSP has remained enigmatic for >30 yr. Recent insight suggests that there are different physiological roles for DMSP based on the cellular DMSP concentrations in producers.Differential production of DMSP was tested with multiple physiological experiments that altered nitrate availability, salinity and temperature to create stressed growth and target different metabolic conditions in Emiliania huxleyi, a high DMSP producer and Thalassiosira oceanica, a low DMSP producer.Emiliania huxleyi intracellular DMSP did not respond to metabolically imbalanced conditions, while Thalassiosira oceanica intracellular DMSP was significantly correlated to stressed growth rate across all conditions tested and exhibited a plastic response on a timescale of hours in nonsteady‐state.The previous assumption that proposed DMSP mechanism(s) can be universally applied to all producers is shown to be unlikely. Rather, two distinct ecological roles for DMSP likely exist that differ by producer type, where: (1) the primary role of DMSP in high producers is a constitutive compatible solute; and (2) DMSP production in low producers is a finely tuned stress response. [ABSTRACT FROM AUTHOR]

Ocean acidification and global warming might affect the production of dimethylsulfoniopropionate (DMSP), dimethylsulfide (DMS), and dissolved acrylic acid (AAd) by marine phytoplankton. Monoculture incubation experiments were conducted with the dinoflagellate Amphidinium carterae to investigate the effects of elevated CO2 concentration and temperature on growth and productions of DMSP, DMS, and AAd. Two pCO2 levels were set as 400 and 1000 μatm, and two temperatures were set as 20 and 23 °C. The growth of A. carterae remained unaffected by an increase of CO2 to 1000 μatm and a rise of temperature of 3 °C. Moreover, the elevated CO2 concentration and temperature had no significant effects on the concentrations and cell-normalized concentrations of DMSP, DMS, and AAd. No additive or synergistic effects of elevated CO2 concentration and temperature on A. carterae were observed, indicating that A. carterae was insensitive to elevated CO2 and temperature in short time incubation. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) and nanoplastics (NPs) have gained global concern due to their detrimental effects on marine organisms. We investigated the effects of 80 nm polystyrene (PS) NPs on life history traits, ingestion, and dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP) production in the rotifer Brachionus plicatilis. Fluorescently labeled 80 nm PS NPs were ingested by the rotifer B. plicatilis and accumulated in the digestive tract. The lethal rates of B. plicatilis exposed to NPs were dose-dependent. High concentrations of PS NPs exposure had negative effects on developmental duration, leading to prolonged embryonic development and pre-reproductive periods, shortened reproductive period, post-reproductive period, and lifespan in B. plicatilis. High concentrations of PS NPs exposure inhibited life table demographic parameters such as age-specific survivorship and fecundity, generation time, net reproductive rate, and life expectancy. Consequently, the population of B. plicatilis was adversely impacted. Furthermore, exposure to PS NPs resulted in a reduced ingestion rate in B. plicatilis , as well as a decreased in DMS, particulate DMSP (DMSP p) concentration, and DMSP lyase activity (DLA), which exhibited a dose-response relationship. B. plicatilis grazing promoted DLA and therefore increased DMS production. PS NPs exposure caused a decline in the increased DMS induced by rotifer grazing. Our results help to understand the ecotoxicity of NPs on rotifer and their impact on the biogeochemical cycle of dimethylated sulfur compounds. [Display omitted] • The lethal rate of Brachionus plicatilis exposed to PS NPs was dose-dependent. • High concentrations of PS NPs had detrimental effects on life history of rotifers. • PS NPs had negative effects on ingestion and DMS and DMSP concentrations. [ABSTRACT FROM AUTHOR]

Abstract Background Climate change causes the breakdown of the symbiotic relationships between reef-building corals and their photosynthetic symbionts (genus Symbiodinium), with thermal anomalies in 2015–2016 triggering the most widespread mass coral bleaching on record and unprecedented mortality on the Great Barrier Reef. Targeted studies using specific coral stress indicators have highlighted the complexity of the physiological processes occurring during thermal stress, but have been unable to provide a clear mechanistic understanding of coral bleaching. Results Here, we present an extensive multi-trait-based study in which we compare the thermal stress responses of two phylogenetically distinct and widely distributed coral species, Acropora millepora and Stylophora pistillata, integrating 14 individual stress indicators over time across a simulated thermal anomaly. We found that key stress responses were conserved across both taxa, with the loss of symbionts and the activation of antioxidant mechanisms occurring well before collapse of the physiological parameters, including gross oxygen production and chlorophyll a. Our study also revealed species-specific traits, including differences in the timing of antioxidant regulation, as well as drastic differences in the production of the sulfur compound dimethylsulfoniopropionate during bleaching. Indeed, the concentration of this antioxidant increased two-fold in A. millepora after the corals started to bleach, while it decreased 70% in S. pistillata. Conclusions We identify a well-defined cascading response to thermal stress, demarking clear pathophysiological reactions conserved across the two species, which might be central to fully understanding the mechanisms triggering thermally induced coral bleaching. These results highlight that bleaching is a conserved mechanism, but specific adaptations linked to the coral’s antioxidant capacity drive differences in the sensitivity and thus tolerance of each coral species to thermal stress.

Dimethylsulfoniopropionate (DMSP) is a ubiquitous organic sulfur compound that underpins sulfur cycling in the marine environment and is the precursor to the climatically active gas dimethylsulfide (DMS). Modelling studies have identified the Southern Ocean as a DMS hot spot during summer, yet except for the bloom forming haptophyte Phaeocystis, little is known about sulfur production by other important members of the marine microbial community. Here, we measured DMSP concentrations and DMSP lyase activity (DLA), with corresponding carbon, nitrogen and Chl a content, in 15 species of Antarctic phototrophic phytoplankton (14 microalgae species and one cyanobacterium) and one phagotrophic flagellate. We found that 11 of the 16 species were able to produce DMSP and eight possess DLA. DMSP content ranged from 0.06 to 73 fmol cell−1 and estimated DMSP production rates ranged from 0.008 to 12.42 fmol cell−1 day−1. As expected, Phaeocystis was amongst the highest producers, however, contrary to expectation DMSP concentrations were high in several pennate diatom species, with intracellular concentrations between 1.85 and 46.6 mM. Here we present the first evidence that the cyanobacterium Synechococcus may be a DMSP producer, with the potential to contribute significantly to the DMSP pool. This study has provided the first analysis of DMSP production and DLA in a suite of phototrophic and phagotrophic species isolated from Antarctica, revealing the variability in DMSP concentrations across multiple strains and within genera and delivered new evidence for potential DLA in diatoms. [ABSTRACT FROM AUTHOR]

Volatile organic sulfur compounds (VOSCs) link the atmospheric, marine, and terrestrial sulfur cycles in marine and marginal marine environments. Despite the important role VOSCs play in global biogeochemical sulfur cycling, less is known about how the local geochemical conditions influence production and consumption of VOSCs. We present a study of dimethyl sulfide (DMS), methanethiol (MeSH), and dimethylsulfoniopropionate (DMSP) in sulfide‐rich (sulfidic) and iron‐rich (ferruginous) salt marsh sediment from north Norfolk, UK. Initial results illustrate the importance of minimizing time between sampling in remote field locations and laboratory analysis, due to rapid degradation of VOSCs. With rapid analysis of sediment from different depths, we observe high concentrations of DMS, MeSH, and DMSP, with concentrations in surface sediment an order of magnitude higher than those in previous studies of surface water. We measure systematic differences in the concentration and depth distribution of MeSH and DMS between sediment environments; DMS concentrations are higher in ferruginous sediment, and MeSH concentrations are higher in sulfidic sediment. With repeated measurements over a short time period, we show that the degradation patterns for DMS and MeSH are different in the ferruginous versus sulfidic sediment. We discuss potential biogeochemical interactions that could be driving the observed differences in VOSC dynamics in ferruginous and sulfidic sediment. Plain Language Summary: Oceans and coastal wetlands are dynamic environments where the carbon, sulfur, and iron biogeochemical cycles are tightly coupled. One important process that occurs in these environments is the formation of organic sulfur gases, which are involved in cloud formation and acid rain. Organic sulfur gases can be formed through a number of biological and chemical pathways, but little is known about how environmental conditions influence the chemical and microbial reactions that form these gases. In this study, we investigate how different chemical environments in salt marsh sediment influence the formation and destruction of organic sulfur gases. Different organic sulfur gases are produced in iron‐rich environments compared to those produced in sulfide‐rich environments. Further, the two geochemical environments also showed different patterns in the breakdown of these gases. These results indicate that the geochemical conditions influence how organic sulfur gases form and how they are released to the atmosphere. These findings have the potential to help explain observed differences in the release of organic sulfur gases among modern‐day environments, as well as how the release of organic sulfur gases may have changed throughout Earth history as environmental conditions evolved. Key Points: Rapid analysis reveals high concentrations of dimethyl sulfide, methanethiol, and dimethylsulfoniopropionate in salt marsh sedimentSulfidic sediment contained higher concentrations of methanethiol, and dimethyl sulfide concentrations were higher in ferruginous sedimentThere are different degradation patterns for dimethyl sulfide and methanethiol based on the geochemistry of the environment [ABSTRACT FROM AUTHOR]

Phaeocystis globosa forms dense, monospecific blooms in temperate, northern waters. Blooms are usually dominated by the colonial morphotype—nonflagellated cells embedded in a secreted mucilaginous mass. Colonial Phaeocystis blooms significantly affect food‐web structure and function and negatively impact fisheries and aquaculture, but factors regulating colony formation remain enigmatic. Destructive P. globosa blooms have been reported in tropical and subtropical regions more recently and warm‐water blooms could become more common with continued climate change and coastal eutrophication. We therefore assessed genetic pathways associated with colony formation by investigating differential gene expression between colonial and solitary cells of a warm‐water P. globosa strain. Our results illustrate a transcriptional shift in colonial cells with most of the differentially expressed genes downregulated, supporting a reallocation of resources associated with forming and maintaining colonies. Dimethylsulfide and acrylate production and pathogen interaction pathways were upregulated in colonial cells, suggesting a defensive role for producing colonies. We identify several protein kinase signaling pathways that may influence the transition between morphotypes, providing targets for future research into factors affecting colony formation. This study provides novel insights into genetic mechanisms involved in Phaeocystis colony formation and provides new evidence supporting a defensive role for Phaeocystis colonies. [ABSTRACT FROM AUTHOR]

The role of copepod Calanus sinicus on the production of dimethylsulfide (DMS)/dimethylsulfoniopropionate (DMSP) in Jiaozhou Bay was evaluated in field measurements and laboratory experiments. Samples at 10 sites in the bay were collected monthly from June 2010 to May 2011 (except for March 2011), and zooplankton species composition was analyzed. Effects of C. sinicus grazing on DMS/DMSP production at different conditions (i.e., algal diets, food concentrations, and salinities) were assessed in the laboratory. Data from the field experiment showed that C. sinicus was the dominant copepod in Jiaozhou Bay (up to 123 individuals/m3 in May 2011) and preferred to graze on diatom. DMS and DMSP concentrations depend on not only phytoplankton abundance but also phytoplankton species and bacterial abundance. In the laboratory experiment, compared with Gymnodinium sp. or Emiliania huxleyi, C. sinicus feeding on Isochrysis galbana and Chaetoceros curvisetus exhibited increased DMS concentration, whereas high salinity inhibited DMS production. Copepod ingested 0.5%–35% of DMSP in filtered phytoplankton, and copepod DMSP ingestion turnover rate in Jiaozhou Bay was up to 29 pmol L−1 d−1. Although the microbial DMSP consumption rate was 10–2,620‐fold of copepod turnover rate, copepod grazing was still one of the important routes in DMSP loss processes through food chain. This study indicated that DMSP was transferred from phytoplankton to copepod body, fecal pellet, and seawater through copepod grazing. Our results provided important information to understand the biogeochemical cycle of DMSP in Jiaozhou Bay. Plain Language Summary: Dimethylsulfide (DMS) is the most abundant biogenic sulfur gas that may influence planetary climate by forming cloud condensation nuclei that alters global radiation balance. Role of copepod Calanus sinicus grazing on DMS production in Jiaozhou Bay were investigated in this study. From the results of in situ study, we found that C. sinicus was the dominant copepod in Jiaozhou Bay, and DMS and dimethylsulfoniopropionate (DMSP) concentrations were related to abundance and species of phytoplankton and zooplankton, and bacterial abundance. Therefore, four algae were used as the diets of C. sinicus to assess the C. sinicus grazing on DMS production. The effects of diet concentration and salinity on feeding rate of C. sinicus and DMS concentration were also investigated. The results showed that C. sinicus preferred to graze on poor‐dimethylsulfoniopropionate algae, and low salinity facilitated DMS production. Dimethylsulfoniopropionate transfer from algae to copepod body and fecal pellet through food chain were also evaluated. The results were helpful to understand the role of copepod on sulfur cycle and further the whole world climate. Key Points: Calanus sinicus was the dominant copepod in Jiaozhou Bay and preferred to graze on diatomCopepod ingestion was an important dimethylsulfoniopropionate loss process, although turnover rate was lower than microbial consumptionCalanus sinicus grazing promoted dimethylsulfide release from dimethylsulfoniopropionate at low salinity [ABSTRACT FROM AUTHOR]

Strain IMCC1322 was isolated from a surface water sample from the East Sea of Korea. Based on 16S rRNA analysis, IMCC1322 was found to belong to the OCS28 sub-clade of SAR116. The cells appeared as short vibrioids in logarithmic-phase culture, and elongated spirals during incubation with mitomycin or in aged culture. Growth characteristics of strain IMCC1322 were further evaluated based on genomic information; proteorhodopsin (PR), carbon monoxide dehydrogenase, and dimethylsulfoniopropionate (DMSP)-utilizing enzymes. IMCC1322 PR was characterized as a functional retinylidene protein that acts as a light-driven proton pump in the cytoplasmic membrane. However, the PR-dependent phototrophic potential of strain IMCC1322 was only observed under CO-inhibited and nutrient-limited culture conditions. A DMSP-enhanced growth response was observed in addition to cultures grown on C1 compounds like methanol, formate, and methane sulfonate. Strain IMCC1322 cultivation analysis revealed biogeochemical processes characteristic of the SAR116 group, a dominant member of the microbial community in euphotic regions of the ocean. The polyphasic taxonomy of strain IMCC1322 is given as Candidatus Puniceispirillum marinum, and was confirmed by chemotaxonomic tests, in addition to 16S rRNA phylogeny and cultivation analyses. [ABSTRACT FROM AUTHOR]

The cycling of the trace gas dimethyl sulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) may be affected by future ocean acidification and warming. DMSP and DMS concentrations were monitored over 20-days in four mesocosm experiments in which the temperature and pH of coastal water were manipulated to projected values for the year 2100 and 2150. This had no effect on DMSP in the two-initial nutrient-depleted experiments; however, in the two nutrient-amended experiments, warmer temperature combined with lower pH had a more significant effect on DMSP & DMS concentrations than lower pH alone. Overall, this indicates that future warming may have greater influence on DMS production than ocean acidification. The observed reduction in DMSP at warmer temperatures was associated with changes in phytoplankton community and in particular with small flagellate biomass. A small decrease in DMS concentration was measured in the treatments relative to other studies, from −2% in the nutrient-amended low pH treatment to −16% in the year 2150 pH and temperature conditions. Temporal variation was also observed with DMS concentration increasing earlier in the higher temperature treatment. Nutrient availability and community composition should be considered in models of future DMS.

The ubiquitous, biogenic trace gas dimethylsulfide (DMS) represents the largest natural source of atmospheric sulfur. Given DMS involvement in cloud formation and climate, understanding and parameterizing the oceanic DMS source and cycling processes is a necessary challenge. We report DMS cycling rates from microzooplankton dilution grazing experiments conducted monthly during 1 year in coastal northwestern Mediterranean waters. Concentrations of DMS, its algal precursor dimethylsulfoniopropionate (DMSPt) and chlorophyll a (Chla) ranged 0.9-11 nmol L−1, 10-71 nmol L−1, and 0.2-1.5 µg L−1, respectively. By comparing the growth and stock production rates of the DMSP-producing algae to those of total phytoplankton, we estimated that 3 ± 4% (range 0.4-12%) of the carbon primary production was invested in DMSP biosynthesis. Microzooplankton grazing rates on DMSP-producing phytoplankton (0.46-1.45 day−1) were generally higher than those on the bulk assemblage (0.08-0.99 day−1), except in midsummer months. This could have been due to the smaller size of most DMSP producers. There was no indication of micrograzer selection against DMSP-containing phytoplankton, since they were not grazed at lower rates than the bulk phytoplankton assemblage. A proportion of 6-20% of the grazed DMSP was converted into DMS, and this grazing-derived production accounted for 32-96% of dark gross DMS production by the total community. Bacteria consumed daily ≤ 14-100% of the gross DMS production, which resulted in biological DMS turnover times of 1 to ≥ 10 days. Throughout the year, grazing-mediated DMS production explained 73% of the variance in the DMS concentration, implying that microzooplankton grazing plays a major role in controlling DMS concentration in surface waters across a broad range of environmental and productivity conditions in the Mediterranean Sea. These findings should help improve the representation of herbivore grazing in prognostic models to predict the distribution and dynamics of the global DMS emission and its feedback response to changing climate. [ABSTRACT FROM AUTHOR]