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In order to evaluate mercury (Hg) accumulation patterns in Southern Ocean penguins, we measured Hg concentrations and carbon (δ 13 C) and nitrogen (δ 15 N) stable isotope ratios in body feathers of adult Adélie (Pygoscelis adeliae), gentoo (Pygoscelis papua), and chinstrap (Pygoscelis antarctica) penguins living near Anvers Island, West Antarctic Peninsula (WAP) collected in the 2010/2011 austral summer. With these and data from Pygoscelis and other penguin genera (Eudyptes and Aptenodytes) throughout the Southern Ocean, we modelled Hg variation using δ 13 C and δ 15 N values. Mean concentrations of Hg in feathers of Adélie (0.09 ± 0.05 μg g -1 ) and gentoo (0.16 ± 0.08 μg g -1 ) penguins from Anvers Island were among the lowest ever reported for the Southern Ocean. However, Hg concentrations in chinstrap penguins (0.80 ± 0.20 μg g -1 ), which undertake relatively broad longitudinal winter migrations north of expanding sea ice, were significantly higher (P < 0.001) than those in gentoo or Adélie penguins. δ 13 C and δ 15 N values for feathers from all three Anvers Island populations were also the lowest among those previously reported for Southern Ocean penguins foraging within Antarctic and subantarctic waters. These observations, along with size distributions of WAP krill, suggest foraging during non-breeding seasons as a primary contributor to higher Hg accumulation in chinstraps relative to other sympatric Pygoscelis along the WAP. δ 13 C values for all Southern Ocean penguin populations, alone best explained feather Hg concentrations among possible generalized linear models (GLMs) for populations grouped by either breeding site (AICc = 36.9, w i  = 0.0590) or Antarctic Frontal Zone (AICc = 36.9, w i  = 0.0537). Although Hg feather concentrations can vary locally by species, there was an insignificant species-level effect (w i  < 0.001) across the full latitudinal range examined. Therefore, feeding ecology at breeding locations, as tracked by δ 13 C, control Hg accumulation in penguin populations across the Southern Ocean., Competing Interests: Declaration of competing interest The authors declare no competing financial interests., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Groundwater contamination by nitrates presents significant risks to both human health and the environment. In groundwater characterized as oligotrophic-low in organic carbon, but abundant in carbonate and phosphate-chemolithoautotrophic bacteria, including nitrate-reducing Fe(II)-oxidizing bacteria (NRFeOB), play a vital role in denitrification. The chemoautotrophic nitrate reduction is sensitive to environmental factors, including widespread iron oxides like hematite in nature. However, the specific mechanisms of this influence remain unclear. We examined the mechanism of how hematite impacts autotrophic nitrate reduction in a model NRFeOB community known as culture KS. We found that hematite enhances the rate of autotrophic nitrate reduction by promoting Fe(II) oxidation. Mössbauer spectroscopy detected a significant amount of adsorbed Fe(II) when hematite was present, leading to a reduction in dissolved ferrous iron. In conjunction with XRD data, it can be inferred that the formation of vivianite decreased, thereby increasing the Fe(II) activity in the reaction system. Within the culture KS bacterial consortium, hematite fosters the proliferation of autotrophic microorganisms, specifically Gallionellaceae, and amplifies the presence of denitrifying microbes, notably Rhodanobacter. This dual enhancement improves Fe(II) utilization and nitrate reduction capabilities. Our findings highlight intricate interactions between hematite and a model NRFeOB community, offering insights into groundwater nitrate removal mechanisms and the ecological strategies of autotrophic bacteria in mineral-rich environments., 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 B.V. All rights reserved.)

The photosynthetic amoeba, Paulinella provides a recent (ca. 120 Mya) example of primary plastid endosymbiosis. Given the extensive data demonstrating host lineage-driven endosymbiont integration, we analysed nuclear genome and transcriptome data to investigate mechanisms that may have evolved in Paulinella micropora KR01 (hereinafter, KR01) to maintain photosynthetic function in the novel organelle, the chromatophore. The chromatophore is of α-cyanobacterial provenance and has undergone massive gene loss due to Muller's ratchet, but still retains genes that encode the ancestral α-carboxysome and the shell carbonic anhydrase, two critical components of the biophysical CO 2 concentrating mechanism (CCM) in cyanobacteria. We identified KR01 nuclear genes potentially involved in the CCM that arose via duplication and divergence and are upregulated in response to high light and downregulated under elevated CO 2 . We speculate that these genes may comprise a novel CO 2 delivery system (i.e., a biochemical CCM) to promote the turnover of the RuBisCO carboxylation reaction and counteract photorespiration. We posit that KR01 has an inefficient photorespiratory system that cannot fully recycle the C 2 product of RuBisCO oxygenation back to the Calvin-Benson cycle. Nonetheless, both these systems appear to be sufficient to allow Paulinella to persist in environments dominated by faster-growing phototrophs., (© 2024 The Author(s). Environmental Microbiology Reports published by John Wiley & Sons Ltd.)

This study aimed to develop surface complexation modeling-machine learning (SCM-ML) hybrid model for chromate and arsenate adsorption on goethite. The feasibility of two SCM-ML hybrid modeling approaches was investigated. Firstly, we attempted to utilize ML algorithms and establish the parameter model, to link factors influencing the adsorption amount of oxyanions with optimized surface complexation constants. However, the results revealed the optimized chromate or arsenate surface complexation constants might fall into local extrema, making it unable to establish a reasonable mapping relationship between adsorption conditions and surface complexation constants by ML algorithms. In contrast, species-informed models were successfully obtained, by incorporating the surface species information calculated from the unoptimized SCM with the adsorption condition as input features. Compared with the optimized SCM, the species-informed model could make more accurate predictions on pH edges, isotherms, and kinetic data for various input conditions (for chromate: root mean square error (RMSE) on test set = 5.90 %; for arsenate: RMSE on test set = 4.84 %). Furthermore, the utilization of the interpretable formula based on Local Interpretable Model-Agnostic Explanations (LIME) enabled the species-informed model to provide surface species information like SCM. The species-informed SCM-ML hybrid modeling method proposed in this study has great practicality and application potential, and is expected to become a new paradigm in surface adsorption model., 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.)

Although sulfur cycling in acid mine drainage (AMD)-contaminated rice paddy soils is critical to understanding and mitigating the environmental consequences of AMD, potential sources and transformations of organosulfur compounds in such soils are poorly understood. We used sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy to quantify organosulfur compounds in paddy soils from five AMD-contaminated sites and one AMD-uncontaminated reference site near the Dabaoshan sulfide mining area in South China. We also determined the sulfur stable isotope compositions of water-soluble sulfate (δ 34 S WS ), adsorbed sulfate (δ 34 S AS ), fulvic acid sulfur (δ 34 S FAS ), and humic acid sulfur (δ 34 S HAS ) in these samples. Organosulfate was the dominant functional group in humic acid sulfur (HAS) in both AMD-contaminated (46%) and AMD-uncontaminated paddy soils (42%). Thiol/organic monosulfide contributed a significantly lower proportion of HAS in AMD-contaminated paddy soils (8%) compared to that in AMD-uncontaminated paddy soils (21%). Within contaminated soils, the concentration of thiol/organic monosulfide was positively correlated with cation exchange capacity (CEC), moisture content (MC), and total Fe (TFe). δ 34 S FAS ranged from -6.3 to 2.7‰, similar to δ 34 S WS (-6.9 to 8.9‰), indicating that fulvic acid sulfur (FAS) was mainly derived from biogenic S-bearing organic compounds produced by assimilatory sulfate reduction. δ 34 S HAS (-11.0 to -1.6‰) were more negative compared to δ 34 S WS , indicating that dissimilatory sulfate reduction and abiotic sulfurization of organic matter were the main processes in the formation of HAS.

Of the six elements incorporated into the major polymers of life, phosphorus is the least abundant on a global scale [E. Anders, M. Ebihara, Geochim. Cosmochim. Acta 46, 2363-2380 (1982)] and has been described as the "ultimate limiting nutrient" [T. Tyrrell, Nature 400, 525-531 (1999)]. In the modern ocean, the supply of dissolved phosphorus is predominantly sustained by the oxidative remineralization/recycling of organic phosphorus in seawater. However, in the Archean Eon (4 to 2.5 Ga), surface waters were anoxic and reducing. Here, we conducted photochemical experiments to test whether photodegradation of ubiquitous dissolved organic phosphorus could facilitate phosphorus recycling under the simulated Archean conditions. Our results strongly suggest that organic phosphorus compounds, which were produced by marine biota (e.g., adenosine monophosphate and phosphatidylserine) or delivered by meteorites (e.g., methyl phosphonate) can undergo rapid photodegradation and release inorganic phosphate into solution under anoxic conditions. Our experimental results and theoretical calculations indicate that photodegradation of organic phosphorus could have been a significant source of bioavailable phosphorus in the early ocean and would have fueled primary production during the Archean eon.

Although it has been established that electron mediators substantially promote extracellular electron transfer (EET), electron shuttling pathways are not fully understood. Here, a new electron shuttling pathway was found in the EET process by Shewanella oneidensis MR-1 with resazurin, a lipophilic electron mediator. With resazurin, the genes encoding outer-membrane cytochromes ( mtrCBA and omcA ) were downregulated. Although cytochrome deletion substantially reduced biocurrent generation to 1-12% of that of wild-type (WT) cells, the presence of resazurin restored biocurrent generation to 168 μA·cm -2 (Δ mtrA / omcA / mtrC ), nearly equivalent to that of WT cells (194 μA·cm -2 ), indicating that resazurin-mediated electron transfer was not dependent on the Mtr pathway. Biocurrent generation by resazurin was much lower in Δ cymA and Δ mtrA / omcA / mtrC / fccA / cctA mutants (4 and 6 μA·cm -2 ) than in WT cells, indicating a key role of FccA, CctA, and CymA in this process. The effectiveness of resazurin in EET of Mtr cytochrome mutants is also supported by cyclic voltammetry, resazurin reduction kinetics, and in situ c -type cytochrome spectroscopy results. The findings demonstrated that low molecular weight, lipophilic electron acceptors, such as phenoxazine and phenazine, may facilitate electron transfer directly from periplasmic and inner membrane proteins, thus providing new insight into the roles of exogenous electron mediators in electron shuttling in natural and engineered biogeochemical systems.

Acid mine drainage (AMD), a source of considerable environmental pollution worldwide, has prompted the development of many strategies to alleviate its effects. Unfortunately, the methods available for remedial treatment of AMD and the damage it cause are generally costly, labor-intensive, and time-consuming. Furthermore, such treatments may result in secondary pollution. Alternatively, treating the AMD problem at its source through pyrite surface passivation has become an important topic for research because it has the potential to reduce or prevent the generation of AMD and associated pollution. This review summarizes various pyrite anti-corrosion technologies, including the formation of various passivating coatings (inorganic, organic and organosilane) and carrier-microencapsulation. Several effective long-term passivators are identified, although many of them currently have important deficiencies that limit their practical application. Combining the mechanisms of existing passivation agents or new artificial materials, while considering environmental conditions, costs, and long-term passivation performance, is a feasible direction for future research., Competing Interests: Declaration of competing interest We declare that we have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Grass shrimp ( Palaemonetes pugio ) represent a potential link in the transfer of methylmercury (MeHg) from salt marsh sediments to transient young-of-the-year (YOY) fish. Across six salt marshes subject to varying degrees of Hg contamination, MeHg concentration in grass shrimp was significantly correlated with MeHg in sediment ( p < 0.05, R 2 = 0.81). Bioenergetic models show that grass shrimp alone account for 12-90% of MeHg observed in YOY striped bass and 6-22% of MeHg in YOY summer flounder. Direct accumulation of MeHg from grass shrimp to YOY fish increased with MeHg levels in grass shrimp and sediment. However, in the most contaminated salt marshes with the highest levels of MeHg in grass shrimp and sediment, indirect accumulation of MeHg from grass shrimp by YOY summer flounder, whose diet is dominated by benthic forage fish (mummichog), is predicted to plateau because higher concentrations of MeHg in grass shrimp are offset by a lower proportion of grass shrimp in the mummichog diet. Our results demonstrate that grass shrimp are an important trophic link in the bioaccumulation of MeHg in salt marsh food webs and that MeHg accumulation in YOY fish varies with both the concentration of MeHg in salt marsh sediments and benthic food web structure.

The inessential heavy metal/loids cadmium (Cd) and arsenic (As), which often co-occur in polluted paddy soils, are toxic to rice. Silicon (Si) treatment is known to reduce Cd and As toxicity in rice plants. To better understand the shared mechanisms by which Si alleviates Cd and As stress, rice seedlings were hydroponically exposed to Cd or As, then treated with Si. The addition of Si significantly ameliorated the inhibitory effects of Cd and As on rice seedling growth. Si supplementation decreased Cd and As translocation from roots to shoots, and significantly reduced Cd- and As-induced reactive oxygen species generation in rice seedlings. Transcriptomics analyses were conducted to elucidate molecular mechanisms underlying the Si-mediated response to Cd or As stress in rice. The expression patterns of the differentially expressed genes in Cd- or As-stressed rice roots with and without Si application were compared. The transcriptomes of the Cd- and As-stressed rice roots were similarly and profoundly reshaped by Si application, suggesting that Si may play a fundamental, active role in plant defense against heavy metal/loid stresses by modulating whole genome expression. We also identified two novel genes, Os01g0524500 and Os06g0514800, encoding a myeloblastosis (MYB) transcription factor and a thionin, respectively, which may be candidate targets for Si to alleviate Cd and As stress in rice, as well as for the generation of Cd- and/or As-resistant plants. This study provides valuable resources for further clarification of the shared molecular mechanisms underlying the Si-mediated alleviation of Cd and As toxicity in rice., (Copyright © 2021. Published by Elsevier B.V.)

Soot and mercury (Hg) are two notorious air pollutants, and the fate and transport of Hg may be affected by soot at various scales in the environment as soot may be both a carrier and a reactant for active Hg species. This study was designed to quantify photoreduction of Hg(II) in the presence of soot and the associated Hg isotope fractionation under both atmospheric aerosol and aqueous conditions (water-saturated). Photoreduction experiments were conducted with diesel soot particulate matter under controlled temperature and relative humidity (RH) conditions using a flow-through semibatch reactor system. Mass-dependent fractionation resulted in the enrichment of heavier Hg isotopes in the remaining Hg(II) with enrichment factors (ε 202 Hg) of 1.48 ± 0.02‰ (±2 standard deviation) to 1.75 ± 0.05‰ for aerosol-phase reactions (RH 28-68%) and from 1.26 ± 0.11 to 1.50 ± 0.04‰ for aqueous-phase reactions. Positive odd mass-independent fractionation (MIF) was observed in aqueous-phase reactions, resulting in Δ 199 Hg values for reactant Hg(II) as high as 5.29‰, but negative odd-MIF occurred in aerosol-phase reactions, in which Δ 199 Hg values of reactant Hg(II) varied from -1.02 to 0‰. The average ratio of Δ 199 Hg/Δ 201 Hg (1.1) indicated that under all conditions, MIF was dominated by magnetic isotope effects during photoreduction of Hg(II). Increasing RH resulted in higher reduction rates but lower extents of negative MIF in the aerosol-phase experiments, suggesting that the reduction of soot particle-bound Hg(II) was responsible for the observed negative odd-MIF. Our results suggest that mass-independent Hg isotope fractionation during Hg(II) photoreduction varies with soot aerosol water content and that Hg-stable isotope ratios may be used to understand the transformational histories of aerosol-bound Hg(II) in the environment.

Bluefin tuna (BFT), highly prized among consumers, accumulate high levels of mercury (Hg) as neurotoxic methylmercury (MeHg). However, how Hg bioaccumulation varies among globally distributed BFT populations is not understood. Here, we show mercury accumulation rates (MARs) in BFT are highest in the Mediterranean Sea and decrease as North Pacific Ocean > Indian Ocean > North Atlantic Ocean. Moreover, MARs increase in proportion to the concentrations of MeHg in regional seawater and zooplankton, linking MeHg accumulation in BFT to MeHg bioavailability at the base of each subbasin's food web. Observed global patterns correspond to levels of Hg in each ocean subbasin; the Mediterranean, North Pacific, and Indian Oceans are subject to geogenic enrichment and anthropogenic contamination, while the North Atlantic Ocean is less so. MAR in BFT as a global pollution index reflects natural and human sources and global thermohaline circulation., Competing Interests: The authors declare no competing interest.

Metal sulfides, which are important indicators of sulfur cycling, are usually divided into two categories according to sulfur chemical valence: (1) monosulfides (S 2- ) and (2) disulfides (S 2 2- ). The two sulfur species are separated and quantified by a sequential-extraction method. Specifically, monosulfides are extracted as acid-volatile sulfide (AVS) using 6 M HCl prior to the extraction of disulfides using acidic CrCl 2 , which is defined as chromium-reducible sulfur (CRS). However, the conventional AVS procedure does not result in the quantitative extraction of S 2- from the acid-insoluble metal monosulfide, copper sulfide (CuS). Consequently, residual sulfur in CuS (CuS-S) may be extracted as CRS resulting in the inaccurate separation of these two sulfur species. In this study, we used stannous chloride (SnCl 2 ) to improve CuS-S recovery in the AVS procedure and permit the separate extraction of sulfur from CuS and pyrite (FeS 2 ), the most abundant disulfide in nature. Our results show that the addition of SnCl 2 increased the recovery of CuS-S as AVS from less than 36% to as high as 92% in the absence of pyrite and Fe 3+ and 89% in the presence of pyrite and Fe 3+ . In addition, based on the observed correlation between the concentration of SnCl 2 and the dissolution of FeS 2 , we identified the appropriate concentration of SnCl 2 needed to avoid the dissolution of FeS 2 in the AVS procedure. SnCl 2 also minimized the oxidation of CuS-S by Fe 3+ released from ferric minerals during the extraction of AVS. Based on the results of a series of sequential-extraction experiments, we show that an amendment of SnCl 2 in the AVS procedure followed by CRS permits the quantitative separation of CuS-S and FeS 2 -S while also preventing interference by Fe 3+ . Our method will find application in research concerned with the fate of metals and the biogeochemistry of sulfur in the 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 © 2021 Elsevier B.V. All rights reserved.)

Arsenic-rich schwertmannite may cause arsenic (As) release during phase transition. In this study, microbial sulfidogenesis on As(V)-loaded schwertmannite (As-Sch) and associated As mobility at different SO 4 2- concentrations were investigated under anaerobic conditions by Desulfosporosinus meridiei (D. meridiei). For biotic treatments, the more SO 4 2- was added, the more Fe 3+ was reduced to Fe 2+ , and the more As(V) was released during the reductive dissolution of As-Sch. The reduction of As(V) to As(III) by D. meridiei resulted in a higher concentration, toxicity, solubility and mobility of As than the corresponding abiotic treatments. However, compared with the abiotic treatments, a variety of new minerals (such as mackinawite, vivianite, sulfur, As 2 S 3 , and parasymplesite) were generated in the biotic treatments, and the As concentration in aqueous solution was less than 1 μM at the end of the incubation period regardless of the presence of SO 4 2- . The results of continuous extraction of different species of As from secondary minerals showed that the effect of microorganisms decreased As content of amorphous iron oxide-bound phase, while increasing that bound on the surface of iron oxide surface-bound phase, thus increasing As fluidity. Our findings indicated that under anaerobic conditions, D. meridiei sulfidogenesis can trigger significant As mobilization in the early stage and remove As from the aqueous solutions when new minerals are formed at a later stage., Competing Interests: Declaration of competing interest None., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Anaerobic bacteria are known to produce neurotoxic methylmercury [MeHg] when elemental mercury [Hg(0)] is provided as the sole mercury source. In this study, we examined the formation of MeHg in anaerobic incubations of sediment collected from the San Jacinto River estuary (Texas, USA) amended with aqueous Hg(0) to investigate the microbial communities involved in the conversion of Hg(0) to MeHg. The results show that the addition of the methanogen inhibitor 2-bromoethanesulfonate (BES) significantly decreased MeHg production. The mercury methylation gene, hgcA, was detected in these sediments using archaeal specific primers, and 16S rRNA sequencing showed that a member of the Methanosarcinaceae family of methanogens was active. These results suggest that methanogenic archaea play an underappreciated role in the production of MeHg in estuarine sediments contaminated with Hg(0)., (© The Author(s) 2020. Published by Oxford University Press on behalf of FEMS.)

How metal-reducing bacteria transfer electrons during dissimilatory energy generation under electron acceptor-limited conditions is poorly understood. Here, we incubated the iron and manganese-reducing bacterium Shewanella oneidensis MR-1 without electron acceptors. Removal of soluble extracellular organic compounds (EOCs) dramatically retarded transfer of electrons to an experimental electron acceptor, Cr(VI), by MR-1. However, the return of either high MW (>3000 Da) or low MW (<3000 Da) soluble EOCs produced by MR-1 to washed cells restored Cr(VI) reduction though Cr(VI) reduction was fastest when both size fractions were added together. Spectral and electrochemical characterization of EOCs indicated the presence of flavins and c -type cytochromes ( c -Cyts). A model of the kinetics of individual elementary reactions between cells, flavins, released c -Cyts, and Cr(VI), including the direct reduction of flavins, released c -Cyts, and Cr(VI) by cells and the indirect reduction of Cr(VI) by reduced forms of flavins and released c -Cyts, was developed. Model results suggest that released c -Cyts could act as electron mediators to accelerate electron transfer from cells to Cr(VI), and the relative contribution of this pathway was higher than that mediated by flavins. Hence, extracellular c -Cyts produced by MR-1 likely play a role in extracellular electron transfer under electron acceptor-limited conditions. These findings provide new insights into extracellular electron shuttling and the metabolic strategy of metal-reducing bacteria under electron acceptor-limited conditions.

The photochemical reduction of Hg(II) is an important pathway in the environmental Hg cycle because it competes with Hg methylation and potentially limits the formation of bioaccumulative methylmercury. Hg stable isotope systematics have proven to be an effective tool for investigating the transport, transformation, and bioaccumulation of Hg. The dominant cause of mass independent isotope fractionation (MIF) of Hg in nature is the photochemical reduction of various species of Hg(II). However, it is difficult to fully interpret Hg stable isotope signatures due to the lack of mechanistic information about which Hg compounds are susceptible to MIF and why. This study investigates Hg isotope fractionation during the photochemical reduction of Hg(II) complexed to organic ligands, which are representative of the available binding sites in natural dissolved organic matter. The photochemical reduction of Hg(II) in the presence of cysteine resulted in both negative and positive MIF in residual Hg(II), where the sign depended on pH and dissolved oxygen level. In the presence of serine, either nuclear volume or magnetic isotope effects were observed depending on the wavelength of light and the extent of Hg(II) complexation by serine. In the presence of ethylenediamine, MIF was negative. Our Hg stable isotope results suggest that MDF and MIF are induced at different steps in the overall photochemical reduction reaction and that MIF does not depend on the rate-determining step but instead depends on photophysical aspects of the reaction such as intersystem crossing and hyperfine coupling. The behavior of Hg isotopes reported here will allow for a better understanding of the underlying reaction mechanisms controlling the Hg isotope signatures recorded in natural samples.

Distinct spatiotemporal distributions of sea surface dissolved elemental mercury (DEM) and its air-sea exchange flux were observed in the river-dominated and monsoon-influenced East China Sea (ECS). Spatially, DEM concentrations were higher in the nearshore Changjiang diluted water (90 ± 20 to 260 ± 40 fM) than in the offshore Kuroshio water (60 ± 10 to 160 ± 40 fM) and correlated with salinity and total Hg concentrations, suggesting that the total Hg discharged from the Changjiang river is a controlling factor. In summer, monsoon-driven coastal upwelling formed a transient nearshore water mass with very elevated DEM concentrations (290 ± 20 to 320 ± 70 fM). Seasonally, DEM concentrations in all water masses were the highest in summer (120 ± 30 to 320 ± 70 fM). Estimated rate coefficients for DEM production varied seasonally and strongly correlated with sea surface temperature (SST). Hg 0 evasion fluxes also peaked in summer (670 ± 380 pmol m -2 day -1 ), while in winter, DEM was close to equilibrium with gaseous elemental mercury in the atmosphere. Based on the air-sea Hg fluxes for all four seasons from this study and regional atmospheric deposition fluxes from others, we conclude that the ECS is a net sink of Hg annually, but it is a source of Hg to the atmosphere in summer. Moreover, the contribution of the ECS to Hg evasion may increase as a result of flood-associated high Changjiang discharge and rising SST.

We investigated the effect of the temporary ban of local industrial activities during the Asia-Pacific Economic Cooperation (APEC) summit (4th-14th Nov 2014) in Beijing, China on total suspended particulate mercury (Hg TSP ) concentrations and isotope compositions. We measured Hg concentrations and isotope ratios in 33 TSP samples from central Beijing, including 21 samples collected from Jun 2012 to Apr 2014, and 12 samples collected from 14th Oct-19th Nov 2014. Volumetric concentrations of both TSP and Hg TSP during the APEC summit were a factor of 2 lower than during the pre-APEC period, indicating substantial reductions in total particulate matter and Hg TSP as a result of emissions controls. However, mass-normalized concentrations and mercury isotope ratios of Hg TSP did not vary significantly between samples collected before, during, or after the APEC summit. These results show that local emissions are important sources of particle bound mercury (PBM) in Beijing and that their control can be used to immediately lower the volumetric concentration of Hg TSP . They also indicate that a similarly complex mixture of sources contributed to PBM in Beijing before and during emissions controls were put in place and that PBM concentrations in Beijing are primarily controlled by emissions and secondarily by photoreduction., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Consistent with the observation that ammonia-oxidizing bacteria (AOB) outnumber ammonia-oxidizing archaea (AOA) in many eutrophic ecosystems globally, AOB typically dominate activated sludge aeration basins from municipal wastewater treatment plants (WWTPs). In this study, we demonstrate that the growth of AOA strains inoculated into sterile-filtered wastewater was inhibited significantly, in contrast to uninhibited growth of a reference AOB strain. In order to identify possible mechanisms underlying AOA-specific inhibition, we show that complex mixtures of organic compounds, such as yeast extract, were highly inhibitory to all AOA strains but not to the AOB strain. By testing individual organic compounds, we reveal strong inhibitory effects of organic compounds with high metal complexation potentials implying that the inhibitory mechanism for AOA can be explained by the reduced bioavailability of an essential metal. Our results further demonstrate that the inhibitory effect on AOA can be alleviated by copper supplementation, which we observed for pure AOA cultures in a defined medium and for AOA inoculated into nitrifying sludge. Our study offers a novel mechanistic explanation for the relatively low abundance of AOA in most WWTPs and provides a basis for modulating the composition of nitrifying communities in both engineered systems and naturally occurring environments.

Jarosite is an iron-hydroxysulfate mineral commonly found in acid mine drainage (AMD). Given its strong adsorption capacity and its ability to co-precipitation with heavy metals, jarosite is considered a potent scavenger of contaminants in AMD-impacted environments. Sulfate-reducing bacteria (SRB) play an important role in the reductive dissolution of jarosite; however, the mechanism involved has yet to be elucidated. In this study, an indigenous SRB community enriched from the Dabaoshan mine area (Guangdong, China) was employed to explore the mechanism of the microbial reduction of jarosite. Different cultures, with or without dissolved sulfate and the physical separation of jarosite from bacteria by dialysis bags, were examined. Results indicate that the reduction of jarosite by SRB occurred via an indirect mechanism. In systems with dissolved sulfate, lactate was incompletely oxidized to acetate coupled with the reduction of SO 4 2- to S 2- , which subsequently reduced the Fe 3+ in jarosite, forming secondary minerals including vivianite, mackinawite and pyrite. In systems without dissolved sulfate, jarosite dissolution occurred prior to reduction, and similar secondary minerals formed as well. Extracellular polymeric substances secreted by SRB appeared to facilitate the release of sulfate from jarosite. Structural sulfate in the solid phase of jarosite may not be available for SRB respiration. Although direct contact between SRB and jarosite is not necessary for mineral reduction, wrapping jarosite into dialysis bags suppressed the reduction to a certain extent. Microbial community composition differed in direct contact treatments and physical separation treatments. Physical separation of the SRB community from jarosite mineral supported the growth of Citrobacter, while Desulfosporosinus dominated in direct contact treatments., (Copyright © 2019 Elsevier B.V. All rights reserved.)

We examined mercury (Hg) accumulation in juvenile and adult subpopulations of Antarctic krill (Euphausia superba) collected west of the Antarctic Peninsula. Samples were collected along a northern cross-shelf transect beginning near Anvers Island and farther south near the sea ice edge in the austral summers of 2011, 2013, 2014, and 2015. Regardless of geographical position, mean concentrations of total Hg and methylmercury (MeHg), the form of Hg that biomagnifies in marine food webs, were significantly higher in juvenile than adult krill in all years. In 2013, juvenile Antarctic krill collected along the coast near Anvers Island had significantly higher MeHg concentrations than krill collected farther offshore, and in 2013 and 2014, coastal juvenile krill exhibited some of the highest MeHg concentrations of all subpopulations sampled. Across all sampling years, collection in northern (sea ice-free) or southern (sea ice edge) transects did not affect MeHg concentrations of juvenile or adult krill, suggesting similar levels and routes of MeHg exposure across the latitudes sampled. Developmental stage, feeding near the coast, and annual variations in sea ice-driven primary and export production were identified as potentially important factors leading to greater MeHg accumulation in juvenile than adult krill. Krill-dependent predators feeding primarily on juveniles may thus accumulate more MeHg than consumers foraging on older krill. These results report MeHg concentrations in Antarctic krill and will be useful for predicting Hg biomagnification in higher-level consumers in this productive Antarctic ecosystem., (Copyright © 2019. Published by Elsevier B.V.)

Size scaling of the accumulation of four trace metals was examined in the infaunal clam Amiantis umbonella in Kuwait Bay. In clams of varying shell length (2.5-5 cm), soft tissue growth in A. umbonella from a contaminated site was inhibited compared with clams from a less contaminated reference site. Body burdens of all four metals were positively correlated with clam soft tissue wet weight, but for Cd, Cu, and Pb, correlations were stronger in clams from the contaminated site (r 2  = 0.6-0.9, p < 0.001) than the reference site (r 2  = 0.2-0.3, p < 0.002). Scaling factors for the accumulation of Cd, Cu, and Pb in the soft tissues of A. umbonella from both sites were not significantly different than 1, indicating that clams accumulated these metals in proportion to growth with little regulation. The scaling factor of Hg in clams from the contaminated site also was 1 but was 0.5 and 2.4 for high and low Hg accumulating subpopulations of clams from the reference site, respectively. The greater retention of Hg with respect to growth in clams from the reference site than from the contaminated site requires further investigation to determine differences in Hg bioavailability at the two sites and the form of Hg these clams accumulate.

Spatial redistribution of legacy mercury (Hg) contamination in the Hackensack River estuary (New Jersey, USA) was evaluated using mercury stable isotopes. Total Hg varied from 0.06 to 3.8 μg g -1 in sediment from the tidal Hackensack River and from 15 to 154 μg g -1 near historically contaminated sites in upper Berry's Creek, a tributary of the Hackensack River. δ 202 Hg values for total Hg from Berry's Creek and Hackensack River estuaries varied over a fairly narrow range (-0.44‰ to -0.21‰), but were highest for sediment from upper Berry's Creek. Isotope mixing plots show that residual legacy mercury from upper Berry's Creek is partially diluted by a low concentration and low δ 202 Hg pool of mercury associated with low organic matter content sediments similar to those in Newark Bay. Based on an isotope mixing model, we estimate that upper Berry's Creek contributes 21%-82% of the mercury in sediments in the Hackensack River estuary and its tidal tributaries, including upstream marsh habitats far from the primary source. Our results show that mercury stable isotopes can be used to track the redistribution of mercury in tidal ecosystems and highlight the potentially large areas which may be affected by legacy mercury contamination in estuaries., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Schwertmannite is an amorphous iron(III)-oxyhydroxysulfate that forms in acid mine drainage (AMD) environments. The characteristic of high heavy metal adsorption capability makes schwertmannite a potentially useful, environmentally friendly material in wastewater treatment. Unstable schwertmannite is prone to recrystallization. Understanding the mechanisms that induce schwertmannite labilization and affect its capacity to remove heavy metals are of great environmental and geochemical significance. Thiocyanate (SCN¯) is a hazardous pseudohalide that is also normally found in AMD. However, little is known about the impact of Fe(III)-binding ligand SCN¯ on schwertmannite stability and its subsequent capacity to bind trace elements. Here, we investigated the adsorption of SCN¯ on schwertmannite and subsequent mineral transformation to characterize this little-known process. The appearance of Fe 2+ indicated that the interactions between schwertmannite and SCN¯ may involve complexation and reduction reactions. Results showed that the majority of the adsorbed-SCN¯ was immobilized on schwertmannite during the 60-days transformation. The transformation rates of schwertmannite increased with increasing concentrations of SCN¯. Goethite was detected as the dominant transformation product with or without SCN¯. The mechanisms of SCN¯-promoted dissolution of schwertmannite can be described as follows: (1) formation of Fe(III)-NCS complexes on the schwertmannite surface and in solution, a process which increases the reactivity of solid phase Fe(III); (2) the extraction of Fe(III) from schwertmannite by SCN¯ and subsequent schwertmannite dissolution; and (3) the formation of secondary minerals from extracted Fe(III). These findings may improve AMD treatment strategies and provide insight into the use and potential reuse of schwertmannite as a trace element sorbent., (Copyright © 2018. Published by Elsevier B.V.)

Cadmium (Cd) and arsenic (As) are nonessential and toxic elements in rice that often occur together in contaminated paddy field soils. To understand whether rice has a common molecular response mechanism against Cd and As toxicity, 30-day seedlings (Oryza sativa L. indica) were exposed separately to Cd and As 3+ in hydroponic cultures for up to 7 days. Root transcriptomic analysis of plants exposed to Cd and As for 3 days revealed that a total of 2224 genes in rice roots responded to Cd stress, while 1503 genes responded to As stress. Of these, 841 genes responded to both stressors. The genes in common to Cd and As stress were associated with redox control, stress response, transcriptional regulation, transmembrane transport, signal transduction, as well as biosynthesis and metabolism of macromolecules and sulfur compounds. In plants exposed to Cd and As separately or in combination for 3 and 7 days, qRT-PCR verification revealed that the glutathione metabolism associated gene Os09g0367700 was significantly up-regulated with respect to unexposed controls and had a positive synergistic effect under combined Cd and As stress. In addition, the redox control related genes Os06g0216000, Os07g0638300 and Os01g0294500, the glutathione metabolism related gene Os01g0530900, the cell wall biogenesis related genes Os05g0247800, Os11g0592000 and Os03g0416200, the expression regulation related genes Os07g0597200 and Os02g0168200, and the transmembrane transport related genes Os04g0524500, also varied significantly with respect to an unexposed control and displayed synergistic effects after 7 days of simultaneous exposure to Cd and As. Our identification of a novel set of genes in rice which responded to both Cd and As 3+ stress may be of value in mitigating the toxicity of co-contaminated soils. These results also provide a deeper understanding of the molecular mechanisms involved in response to multi-metal/loids stress, and may be used in the genetic improvement of rice varieties., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Schwertmannite is an important sink for cadmium (Cd) in acid mine drainage (AMD) environments and is unstable when environmental conditions change. However, the release and redistribution of Cd during schwertmannite transformation with respect to pre-bound Cd are poorly understood. In this work, the transformation of cadmium-associated schwertmannite and subsequent Cd repartitioning behaviors were investigated. The way of schwertmannite associated with Cd was predominant by absorption, and the diffuse layer model (DLM) showed that Cd 2+ existed as monodentate complexes ≡Fe (1) OCd + and ≡Fe (2) OCd + on schwertmannite surfaces. Kinetics of SO 4 2- release and mineralogical characterization both showed that the mineral transformation rates decreased and more lepidocrocite aggregated with increasing adsorbed Cd levels. The shrinking core model revealed that Fe(II)-induced process would affect mineral dissolution by changing surface reaction-controlled step to internal diffusion-controlled step, and significantly promote the dissolution rate of Cd-adsorbed schwertmannite. Adsorbed Cd blocked the surface sites for later Fe(II) adsorption and the Fe(II)-Fe(III) electron transfer, then resulted in the decelerated transformation and the accumulation of intermediate phase lepidocrocite. The maximum release of aqueous Cd occurred after 1 mM Fe 2+ addition, then over 69% of initial added Cd (aq) re-bound to solid-phase accompanying with mineral transformation, and finally, Cd was mainly associated with the secondary minerals by complexation with surficial OH groups. These findings are useful for developing the strategies for treating Cd contamination in AMD affected areas.

Understanding the mechanism of the microbial transformation of Fe(III)-oxyhydroxysulfate minerals is of considerable interest, because this transformation plays an important role in controlling the behaviour of toxic metals from acid mine drainage (AMD). In this study, we examined a sulfate reducing enrichment culture from AMD-contaminated sediments and predicted the possible pathway of electron transfer when incubated with schwertmannite, a common Fe(III)-oxyhydroxysulfate occurring in the AMD environment. Experiments were designed to distinguish the mechanisms by which bacteria facilitate direct (i.e., bacteria allowed to adhere to the mineral) or indirect (i.e., bacteria separated from the mineral by dialysis bag) electron transfer to reduce the mineral. The effects of adding anthraquinone-2,6-disulfonate (AQDS) as an exogenous electron shuttle were also investigated. Vivianite was detected as the main product of schwertmannite transformation. Reduction of sulfate and iron were more pronounced in direct treatments, while more non-reductive dissolution were observed in indirect treatments. The addition of AQDS lead to the production of more dissolved Fe 2+ over 20 d than in the absence of AQDS. Microbial community composition differed in direct and indirect treatments, while the addition of AQDS did not significantly affect the community structure in each treatment. After incubation for 20 d, the growth of Desulfovibrio exceeded that of the originally dominant Citrobacter in direct treatments, while an unknown genus most closely related to Citrobacter within Enterobacteriaceae was predominant in indirect treatments. This monodominant community in indirect treatments was assumed not to transfer electron directly to schwertmannite but to rely on shuttling mechanism. PICRUSt results implied that bacteria in indirect treatment have potential to produce shuttling compounds or complexing agents. The absence of dsr genes and the putative fermentative process suggested that the Enterobacteriaceae might indirectly facilitate the dissolution and transformation of schwertmannite., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Exposure to dietary sources of methylmercury (MeHg) is the focus of public health concerns with environmental mercury (Hg) contamination. MeHg is formed in anoxic environments by anaerobic microorganisms. This process has been studied mostly with single-species culture incubations, although the relevance of such studies to Hg(II)-methylation in situ is limited because microbial activities in the environment are critically modulated by interactions among microbial functional groups. Here we describe experiments in which Hg(II)-methylation was examined within the context of various microbial syntrophies. We show enhanced Hg(II)-methylation under conditions that established syntrophy by interspecies hydrogen and acetate transfer. Relative to activity of monocultures, interactions of Hg(II) methylating sulfate-reducing bacteria with a methanogen stimulated potential Hg(II)-methylation rates 2-fold to 9-fold, and with Syntrophobacter sp. 1.7-fold to 1.8-fold; those of a Hg(II) methylating Syntrophobacter sp. with a methanogen increased Hg(II)-methylation 2-fold. Under sulfate-depleted conditions, higher Hg(II)-methylation rates in the syntrophic incubations corresponded to higher free energy yields (ΔG°') than in the monocultures. Based on energetic considerations, we therefore propose that syntrophic microbial interactions are likely a major source of MeHg in sulfate- and iron-limited anoxic environments while in sulfate-replete environments, MeHg formation via sulfate reduction dominates.

Schwertmannite, a Fe(III)-oxyhydroxysulfate mineral formed in acidic (pH 3~4), iron- and sulfate-rich acid mine drainage (AMD) environments, tends to undergo phase transformations with changes in pH and redox condition, which may depend on the presence of various trace anions and cations. In the present study, the effects of Cu(II) on the stability of arsenate-, chromate-, and molybdate-substituted schwertmannite were investigated. The release of Fe(III) and sulfate from schwertmannite seems to be accelerated in the presence of Cu(II) at pH ~ 3, while Cu(II) retarded the dissolution of schwertmannite at pH ~ 5. XRD and SEM results showed that pure schwertmannite and chromate-substituted schwertmannite underwent transformation to goethite over a 2-month period, the presence of Cu(II) enhanced the stability of the mineral's structure at both pH 3 and 5. However, the structures of arsenate- and molybdate-substituted schwertmannites showed no significant changes in the presence or absence of Cu(II) at both pH 3 and 5. During the phase transformation process, the amount of released oxyanions followed the sequence of chromate > molybdate > arsenate. Moreover, the release of arsenate and chromate from schwertmannite was retarded in the presence of Cu(II) at pH 5, whereas the release of molybdate was promoted. These results have important environmental implications for the stability of schwertmannite and its potential to immobilize contaminant trace elements under AMD conditions.

Lacking sufficient clean water, the paddy soils along the Hengshi River have suffered from long-term acid mine drainage (AMD) contamination. The impacted cropland is too heavily contaminated to grow food safely. The microbial communities inhabiting the environment play pivotal roles in the crop growth, health, and ecological services. In this study, the bacterial, archaeal, and fungal communities in the impacted paddy soil were examined using high-throughput Illumina MiSeq sequencing. The results showed that AMD irrigation considerably enriched the bacterial phylum Acidobacteria and the archaeal phylum Crenarchaeota, while the fungal community was more stable. The abundances of Acidobacteria and Crenarchaeota were significantly positively correlated with the AMD-related environmental factors of pH and heavy metals (Cu, Pb, and Zn). In the most contaminated samples, communities were dominated by the bacteria Candidatus Solibacter and Candidatus Koribacter from the Acidobacteria family. Functional gene profile analysis demonstrated that the energy metabolic processes of the microbial communities, especially C/N related pathways, have adjusted and are well-adapted to tolerating AMD contamination. The present study described the structural and functional differentiation of microbial communities in the rice paddy soil under AMD irrigation. The results are useful for the development of bioremediation strategies using native microbes in the cleanup and biorestoration of AMD-contaminated agriculture soil., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The emergence and spread of antibiotic-resistant pathogenic bacteria is currently one of the most serious challenges to human health. To combat this problem, it is critical to understand the processes and pathways that result in the creation of antibiotic resistance gene pools in the environment. In this study, we examined the effects of mercury (Hg) exposure on the co-selection of Hg and antibiotic-resistant bacteria that colonize the gastrointestinal tract of the mummichog (Fundulus heteroclitus), a small, estuarine fish. We examined this connection in two experimental systems: (i) a short-term laboratory exposure study where fish were fed Hg-laced food for 15 days and (ii) an examination of environmental populations from two sites with very different levels of Hg contamination. In the lab exposure study, fish muscle tissue accumulation of Hg was proportional to food Hg concentration (R 2  = 0.99; P < 0.0001). In the environmental study, fish from the contaminated site contained threefold more Hg compared to fish from the reference site (P < 0.05). Further, abundance of the Hg resistance gene mercuric reductase was more than eightfold higher (P < 0.0001) in DNA extracts of ingesta of fish from the contaminated site, suggesting adaptation to Hg. Finally, resistance to three or more antibiotics was more common in Hg-resistant as compared to Hg-sensitive bacterial colonies that were isolated from fish ingesta (P < 0.001) demonstrating co-selection of Hg and antibiotic resistances. Together, our results highlight the possibility for the creation of antibiotic resistance gene pools as a result of exposure to Hg in contaminated environments.

The biological production of monomethylmercury (MeHg) in soils and sediments is an important factor controlling mercury (Hg) accumulation in aquatic and terrestrial food webs. In this study we examined the fractionation of Hg stable isotopes during Hg methylation in nongrowing cultures of the anaerobic bacteria Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132. Both organisms showed mass-dependent, but no mass-independent fractionation of Hg stable isotopes during Hg methylation. Despite differences in methylation rates, the two bacteria had similar Hg fractionation factors (αr/p = 1.0009 and 1.0011, respectively). Unexpectedly, δ(202)Hg values of MeHg for both organisms were 0.4‰ higher than the value of initial inorganic Hg after about 35% of inorganic Hg had been methylated. These results indicate that a (202)Hg-enriched pool of inorganic Hg was preferentially utilized as a substrate for methylation by these organisms, but that multiple intra- and/or extracellular pools supplied inorganic Hg for biological methylation. Understanding the controls of the Hg stable isotopic composition of microbially produced MeHg is important to identifying bioavailable Hg in natural systems and the interpretation of Hg stable isotopes in aquatic food webs.

Mercury resistant bacteria play a critical role in mercury biogeochemical cycling in that they convert methylmercury (MeHg) and inorganic mercury to elemental mercury, Hg(0). To date there are very few studies on the effects of speciation and bioavailability of MeHg in these organisms, and even fewer studies on the role that binding to cellular ligands plays on MeHg uptake. The objective of this study was to investigate the effects of thiol complexation on the uptake of MeHg by measuring the intracellular demethylation-reduction (transformation) of MeHg to Hg(0) in Hg-resistant bacteria. Short-term intracellular transformation of MeHg was quantified by monitoring the loss of volatile Hg(0) generated during incubations of bacteria containing the complete mer operon (including genes from putative mercury transporters) exposed to MeHg in minimal media compared to negative controls with non-mer or heat-killed cells. The results indicate that the complexes MeHgOH, MeHg-cysteine, and MeHg-glutathione are all bioavailable in these bacteria, and without the mer operon there is very little biological degradation of MeHg. In both Pseudomonas stutzeri and Escherichia coli, there was a pool of MeHg that was not transformed to elemental Hg(0), which was likely rendered unavailable to Mer enzymes by non-specific binding to cellular ligands. Since the rates of MeHg accumulation and transformation varied more between the two species of bacteria examined than among MeHg complexes, microbial bioavailability, and therefore microbial demethylation, of MeHg in aquatic systems likely depends more on the species of microorganism than on the types and relative concentrations of thiols or other MeHg ligands present.

As mercury (Hg) biosensors are sensitive to only intracellular Hg, they are useful in the investigation of Hg uptake mechanisms and the effects of speciation on Hg bioavailability to microbes. In this study, bacterial biosensors were used to evaluate the roles that several transporters such as the glutathione, cystine/cysteine, and Mer transporters play in the uptake of Hg from Hg-thiol complexes by comparing uptake rates in strains with functioning transport systems to strains where these transporters had been knocked out by deletion of key genes. The Hg uptake into the biosensors was quantified based on the intracellular conversion of inorganic mercury (Hg(II)) to elemental mercury (Hg(0)) by the enzyme MerA. It was found that uptake of Hg from Hg-cysteine (Hg(CYS)2) and Hg-glutathione (Hg(GSH)2) complexes occurred at the same rate as that of inorganic complexes of Hg(II) into Escherichia coli strains with and without intact Mer transport systems. However, higher rates of Hg uptake were observed in the strain with a functioning Mer transport system. These results demonstrate that thiol-bound Hg is bioavailable to E. coli and that this bioavailability is higher in Hg-resistant bacteria with a complete Mer system than in non-resistant strains. No difference in the uptake rate of Hg from Hg(GSH)2 was observed in E. coli strains with or without functioning glutathione transport systems. There was also no difference in uptake rates between a wildtype Bacillus subtilis strain with a functioning cystine/cysteine transport system, and a mutant strain where this transport system had been knocked out. These results cast doubt on the viability of the hypothesis that the entire Hg-thiol complex is taken up into the cell by a thiol transporter. It is more likely that the Hg in the Hg-thiol complex is transferred to a transport protein on the cell membrane and is subsequently internalized.

The mechanisms of carbon concentration in marine diatoms are controversial. At low CO2 , decreases in O2 evolution after inhibition of phosphoenolpyruvate carboxylases (PEPCs), and increases in PEPC transcript abundances, have been interpreted as evidence for a C4 mechanism in Thalassiosira pseudonana, but the ascertainment of which proteins are responsible for the subsequent decarboxylation and PEP regeneration steps has been elusive. We evaluated the responses of T. pseudonana to steady-state differences in CO2 availability, as well as to transient shifts to low CO2 , by integrated measurements of photosynthetic parameters, transcript abundances and quantitative proteomics. On shifts to low CO2 , two PEPC transcript abundances increased and then declined on timescales consistent with recoveries of Fv /Fm , non-photochemical quenching (NPQ) and maximum chlorophyll a-specific carbon fixation (Pmax ), but transcripts for archetypical decarboxylation enzymes phosphoenolpyruvate carboxykinase (PEPCK) and malic enzyme (ME) did not change. Of 3688 protein abundances measured, 39 were up-regulated under low CO2 , including both PEPCs and pyruvate carboxylase (PYC), whereas ME abundance did not change and PEPCK abundance declined. We propose a closed-loop biochemical model, whereby T. pseudonana produces and subsequently decarboxylates a C4 acid via PEPC2 and PYC, respectively, regenerates phosphoenolpyruvate (PEP) from pyruvate in a pyruvate phosphate dikinase-independent (but glycine decarboxylase (GDC)-dependent) manner, and recuperates photorespiratory CO2 as oxaloacetate (OAA)., (© 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.)

Methylmercury (MeHg), a neurotoxic substance that accumulates in aquatic food chains and poses a risk to human health, is synthesized by anaerobic microorganisms in the environment. To date, mercury (Hg) methylation has been attributed to sulfate- and iron-reducing bacteria (SRB and IRB, respectively). Here we report that a methanogen, Methanospirillum hungatei JF-1, methylated Hg in a sulfide-free medium at comparable rates, but with higher yields, than those observed for some SRB and IRB. Phylogenetic analyses showed that the concatenated orthologs of the Hg methylation proteins HgcA and HgcB from M. hungatei are closely related to those from known SRB and IRB methylators and that they cluster together with proteins from eight other methanogens, suggesting that these methanogens may also methylate Hg. Because all nine methanogens with HgcA and HgcB orthologs belong to the class Methanomicrobia, constituting the late-evolving methanogenic lineage, methanogenic Hg methylation could not be considered an ancient metabolic trait. Our results identify methanogens as a new guild of Hg-methylating microbes with a potentially important role in mineral-poor (sulfate- and iron-limited) anoxic freshwater environments.

The objectives of this study were to evaluate the infaunal, facultative deposit-feeding clam Amiantis umbonella as a bioindicator of trace-metal contamination and the relative importance of clam burrow sediment and porewater to total accumulation in an urban/industrial coastal environment. Concentrations of eight trace metals (cadmium [Cd], chromium, copper, mercury [Hg], nickel, lead [Pb], vanadium, and zinc) were measured in the soft tissues of clams and in sediment and porewater from clam burrows along a 5-km transect from desalination/power plant discharges in inner Kuwait Bay. All metals had significantly greater concentrations in clams collected near the desalination/power plant discharges than from the reference site and exhibited decreasing trends with distance from the point source in clam soft tissues and burrow sediment and porewater. Concentrations of Hg (1-9 ppm [dry weight]) and the highest concentrations of Pb (3 ppm) and Cd (7 ppm) in clams from contaminated sites in Kuwait Bay were greater than human consumption limits. Metal concentrations in clams were correlated with those in burrow sediment and porewater across all sites and at sites closest to the point source but not within the reference site. The concentrations of all metals, except Pb, in clams from the contaminated sites were more highly correlated with those in clam burrow sediment than porewater. Concentrations of Pb in clam soft tissues were more strongly correlated with those in burrow porewater than sediment. These results indicate that A. umbonella is an excellent bioindicator of trace metal contamination and that sediment is an important source of contaminant metals to this infaunal clam; however, the source of each metal must be evaluated separately.

The accumulation of inorganic carbon from seawater by eukaryotic marine phytoplankton is limited by the diffusion of carbon dioxide (CO2) in water and the dehydration kinetics of bicarbonate to CO2 and by ribulose-1,5-bisphosphate carboxylase/oxygenase's (RubisCO) low affinity for its inorganic carbon substrate, CO2. Nearly all marine phytoplankton have adapted to these limitations and evolved inorganic carbon (or CO2) concentrating mechanisms (CCMs) to support photosynthetic carbon fixation at the concentrations of CO2 present in ocean surface waters (< 10-30 microM). The biophysics and biochemistry of CCMs vary within and among the three dominant groups of eukaryotic marine phytoplankton and may involve the activity of external or intracellular carbonic anhydrase, HCO3- transport, and perhaps a C4 carbon pump. In general, coccolithophores have low-efficiency CCMs, and diatoms and the haptophyte genus Phaeocystis have high-efficiency CCMs. Dinoflagellates appear to possess moderately efficient CCMs, which may be necessitated by the very low CO2 affinity of their form II RubisCO. The energetic and nutrient costs of CCMs may modulate how variable CO2 affects primary production, element composition, and species composition of phytoplankton in the ocean.

Analysis of arsenic concentrations in New Jersey well water from the Newark Basin showed up to 15% of the wells exceed 10 microg L(-1), with a maximum of 215 microg L(-1). In some geologic settings in the basin, this mobile arsenic could be from the weathering of pyrite (FeS2) found in black shale that contains up to 4% arsenic by weight. We hypothesized that under oxic conditions at circumneutral pH, the microbially mediated oxidation of sulfide in the pyrite lattice would lead to the release of pyrite-bound arsenic. Moreover, the oxidation of aqueous As(III) to As(V) by aerobic microorganisms could further enhance arsenic mobilization from the solid phase. Enrichment cultures under aerobic, As(III)-oxidizing conditions were established under circumneutral pH with weathered black shale from the Newark Basin as the inoculum source. Strain WAO, an autotrophic inorganic-sulfur and As(III)-oxidizer, was isolated and phylogenetically and physiologically characterized. Arsenic mobilization studies from arsenopyrite (FeAsS) mineral, conducted with strain WAO at circumneutral pH, showed microbially enhanced mobilization of arsenic and complete oxidation of released arsenic and sulfur to stoichiometric amounts of arsenate and sulfate. In addition, WAO preferentially colonized pyrite on the surface of arsenic-bearing, black shale thick sections. These findings support the hypothesis that microorganisms can directly mobilize and transform arsenic bound in mineral form at circumneutral pH and suggest that the microbial mobilization of arsenic into groundwater may be important in other arsenic-impacted aquifers.

Speciation and reactivity of mercury were examined in Berry's Creek estuary downstream of a highly mercury-contaminated U.S. EPA Superfund site during the summers of 2002 and 2003. Surface water samples from Berry's Creek estuary, its confluence with the Hackensack River, and upstream of that confluence were analyzed for total (THg), particulate (PHgT), and dissolved (DHg) mercury, total and particulate monomethylmercury (MeHg), dissolved gaseous mercury (DGM), and bacterial merA gene and transcript abundances. Surface water concentrations of THg in Berry's Creek estuary (210-6800 pM) are among the highest in North America. A downstream gradient of Hg contamination is a permanent feature of Berry's Creek estuary, and the upper estuary appears to be a perennial source of Hg to the lower estuary and the Hackensack River. MeHg concentrations in Berry's Creek surface waters ranged from 2 to 14 pM, with the highest concentrations occurring at a midestuary site 2 km downstream of the tide gate. The suspended particle phase dominated Hg and MeHg speciation throughout this system, accounting for > 90% of THg in Berry's Creek estuary and 35-94% of THg in the Hackensack River. Concentrations of DGM in Berry's Creek estuary (0.1-1.0 pM) are similar to levels of DGM in other much less contaminated estuaries (0.04-0.75 pM). In addition, expression levels of the bacterial mercuric reductase gene, merA, a gene of the inorganic Hg(II)-regulated, mercury resistance (mer) operon, were low throughout Berry's Creek estuary. Thus, despite very high concentrations of mercury in Berry's Creek estuary, relatively low concentrations of DGM and merA gene expression levels indicate limited bioavailability of inorganic Hg in the estuary's surface waters. A system-wide limitation on the bioavailability of inorganic Hg, together with bacterial demethylation activity, may account for observed MeHg concentrations that, although elevated, are lower than expected given the concentrations of THg in this estuary.

Superoxide dismutase (SOD) catalyzes the transformation of superoxide to molecular oxygen and hydrogen peroxide. Of the four known SOD isoforms, distinguished by their metal cofactor (iron, manganese [Mn], copper/zinc, nickel), MnSOD is the dominant form in the diatom Thalassiosira pseudonana. We cloned the MnSOD gene, sodA, using the expression vector pBAD, overexpressed the product in Escherichia coli, and purified the mature protein (TpMnSOD). This recombinant enzyme was used to generate a polyclonal antibody in rabbit that recognizes MnSOD in T. pseudonana. Based on quantitative immunoblots, we calculate that in vivo concentrations of TpMnSOD are approximately 0.9 amol cell(-1) using the recombinant protein as a standard. Immunogold staining indicates that TpMnSOD is localized in the chloroplasts, which is in contrast to most other eukaryotic algae (including chlorophytes and embryophytes) where MnSOD is localized exclusively in mitochondria. Based on the photosynthetic Mn complex in photosystem II, cellular Mn budgets cannot account for 50% to 80% of measured Mn within diatom cells. Our results reveal that chloroplastic MnSOD accounts for 10% to 20% of cellular Mn, depending on incident light intensity and cellular growth rate. Indeed, our analysis indicates that TpMnSOD accounts for 1.4% (+/-0.2%) of the total protein in the cell. The TpMnSOD has a rapid turnover rate with an apparent half-life of 6 to 8 h when grown under continuous light. TpMnSOD concentrations increase relative to chlorophyll, with an increase in incident light intensity to minimize photosynthetic oxidative stress. The employment of a Mn-based SOD, linked to photosynthetic stress in T. pseudonana, may contribute to the continued success of diatoms in the low iron regions of the modern ocean.

Upland placement of dredged materials from navigation channels in the New York/New Jersey Harbor is currently being used to manage sediments deemed inappropriate for open water disposal. Although upland placement sites are equipped with engineering controls (leachate collection and/or barrier walls), little is known of the potential impacts of this approach to air quality. The aim of this study was to estimate the flux of mercury to the atmosphere from New York/New Jersey Harbor stabilized dredged material (SDM) that was used for land reclamation at a site in northeastern New Jersey. Total gaseous mercury (TGM) was measured at a site receiving SDM in August and October 2001 and May and November 2002. TGM was also monitored at an urban reference site 3.5 km west of the SDM site in September 2001 and from February 2002 to July 2002 and from October 2002 to February 2003. The concentration of TGM at the urban reference site averaged 2.2 +/- 1.1 ng m(-3), indicating some local contribution to the Northern Hemisphere background. TGM concentrations exhibited seasonality with the highest values in summer (3.3 +/- 2.1 ng m(-3) in June 2002) and the lowest in winter (1.7 +/- 0.6 ng m(-3) in January 2003). TGM concentrations at the SDM placement site ranged from 2 to 7 ng m(-3) and were significantly higher (p < 0.001) than those at the urban reference site. Sediment-air fluxes of Hg at the SDM placement site estimated by the micrometeorological technique ranged from -13 to 1040 ng m(-2) h(-1) (sediment to air fluxes being positive) and were significantly correlated to solar radiation (r2 = 0.81). The estimated contribution of Hg emissions from land-applied SDM to local TGM concentrations was found to be negligible (<4%). However, the estimated annual volatilization rate of TGM atthe SDM site (130 kg y(-1))was comparable to those of other industrial sources in New Jersey (140-450 kg y(-1)).

Atmospheric concentrations of polycyclic aromatic hydrocarbons (PAHs) were measured at urban/industrial, suburban, coastal, and rural areas in New Jersey as part of the New Jersey Atmospheric Deposition Network. Concentrations of 36 PAH compounds were measured in the gas and particle phases in air and in precipitation at nine sites at regular intervals from October 1997 through May 2001. Gas-phase and particle-phase sigma36PAH concentrations ranged from 0.45 to 118 ng m(-3) and from 0.046 to 172 ng m(-3), respectively, and precipitation concentrations ranged from 11 to 16200 ng L(-1). PAH concentrations vary spatially across the region, with the highest concentrations occurring at the most heavily urban and industrial locations. Average gas absorption deposition ranged from 0.004 (naphthacene) to 5040 (methylphenanthrenes) ng m(-2) d(-1), and dry particle deposition PAH fluxes ranged from 0.11 (naphthacene) to 300 (benzo[b+k]fluoranthene) ng m(-2) d(-1) at the nine sites. Average atmospheric wet deposition PAH fluxes at the seven sites ranged from 0.40 (cyclopenta[cd]pyrene) to 140 (methylphenanthrenes) ng m(-2) d(-1). These represent the first comprehensive estimates of PAH deposition to New Jersey and the Mid-Atlantic East Coast.

The curious phenomenon of similar levels of methylmercury (MeHg) accumulation in fish from contaminated and pristine environments may be explained by the observation that the proportion of total mercury (HgT) present as MeHg is inversely related to HgT in natural waters. We hypothesize that this "MeHg accumulation paradox" is explained by the quantitative induction of bacterial enzymes that are encoded by the mercury resistance (mer) operon, organomercury lyase (MerB), and mercuric reductase (MerA) by inorganic Hg (Hg[II]). We tested this hypothesis in two ecosystems in New Jersey: Berry's Creek in the Meadowlands (ML) and Pine Barren (PB) lakes. Across all sites, an inverse correlation (r2 = 0.80) between the concentration of HgT (ML, 113-4220 ng L(-1); PB, 0.3-5.4 ng L(-1)) and the proportion of HgT as MeHg (MeHg in ML and PB ranged from 0.08 to 1.6 and from 0.03 to 0.34 ng L(-1), respectively) was observed. The planktonic microbial community in Meadowlands surface waters exhibited adaptation to mercury, the presence of mer genes and mRNA transcripts, and high rates of reductive demethylation (k(deg) = 0.19 day(-1)). In contrast, the microbial community of PB was not adapted to mercury and demonstrated low rates of oxidative demethylation (k(deg) = 0.01 day(-1)). These results strongly support our hypothesis and show that the degradation of MeHg by mer-encoded enzymes by the water column microbiota of contaminated environments can significantly affect the amount of MeHg that is available for entry into the aquatic food web.

The role of a C(4) pathway in photosynthetic carbon fixation by marine diatoms is presently debated. Previous labeling studies have shown the transfer of photosynthetically fixed carbon through a C(4) pathway and recent genomic data provide evidence for the existence of key enzymes involved in C(4) metabolism. Nonetheless, the importance of the C(4) pathway in photosynthesis has been questioned and this pathway is seen as redundant to the known CO(2) concentrating mechanism of diatoms. Here we show that the inhibition of phosphoenolpyruvate carboxylase (PEPCase) by 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate resulted in a more than 90% decrease in whole cell photosynthesis in Thalassiosira weissflogii cells acclimated to low CO(2) (10 microm), but had little effect on photosynthesis in the C(3) marine Chlorophyte, Chlamydomonas sp. In 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate-treated T. weissflogii cells, elevated CO(2) (150 microm) or low O(2) (80-180 microm) restored photosynthesis to the control rate linking PEPCase inhibition with CO(2) supply in this diatom. In C(4) organic carbon-inorganic carbon competition experiments, the (12)C-labeled C(4) products of PEPCase, oxaloacetic acid and its reduced form malic acid suppressed the fixation of (14)C-labeled inorganic carbon by 40% to 50%, but had no effect on O(2) evolution in photosynthesizing diatoms. Oxaloacetic acid-dependent O(2) evolution in T. weissflogii was twice as high in cells acclimated to 10 microm rather than 22 microm CO(2), indicating that the use of C(4) compounds for photosynthesis is regulated over the range of CO(2) concentrations observed in marine surface waters. Short-term (14)C uptake (silicone oil centrifugation) and CO(2) release (membrane inlet mass spectrometry) experiments that employed a protein denaturing cell extraction solution containing the PEPCKase inhibitor mercaptopicolinic acid revealed that much of the carbon taken up by diatoms during photosynthesis is stored as organic carbon before being fixed in the Calvin cycle, as expected if the C(4) pathway functions as a CO(2) concentrating mechanism. Together these results demonstrate that the C(4) pathway is important in carbon accumulation and photosynthetic carbon fixation in diatoms at low (atmospheric) CO(2).

The first estimates of atmospheric deposition fluxes of polychlorinated biphenyls (PCBs) to the Hudson River Estuary are presented. Concentrations of PCBs were measured in air, aerosol, and precipitation at nine sites representing a variety of land-use regimes at regular intervals from October 1997 through May 2001. Highest concentrations in the gas phase were observed at urban sites such as Camden and Jersey City (sigmaPCB concentrations averaged 3250 and 1260 pg m(-3), respectively). In great portions of the state encompassing forested, coastal, and suburban environments, gas-phase sigmaPCB concentrations were essentially the same (averaging 150-220 pg m(-3)). This spatial trend suggests that atmospheric PCBs arise from highly localized, urban sources which influence atmospheric concentrations and deposition fluxes over a distance of a few tens of kilometers. Atmospheric sigmaPCB deposition fluxes (gas absorption + dry particle deposition + wet deposition) ranged from 7.3 to 340 microg m(-2) yr(-1) and increased with proximity to urban areas. While the magnitude of the fluxes increased with urbanization,the relative proportions of wet, dry, and gaseous deposition remained largely constant. Because the Hudson River Estuary is adjacent to urban areas such as Jersey City, it is subject to higher depositional fluxes of PCBs. These depositional fluxes are at least 2-10 times those estimated for the Chesapeake Bay and Lake Michigan. Inputs of PCBs to the Hudson River Estuary from the upper Hudson River and from wastewater treatment plants are 8-18 times atmospheric inputs, and volatilization of PCBs from the estuary exceeds atmospheric deposition of low molecular weight PCBs.