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Several microalgae, including marine diatoms, significantly contribute to the global primary production and play a vital role in the food webs of benthic and planktonic ecosystems. Diatoms of the genus Cocconeis frequently inhabit benthic substrates, including the leaves of seagrasses. They are seasonally dominant in the leaf epiphytic layer of the Mediterranean seagrass Posidonia oceanica L. Delile, and have been proposed as model organisms for chemical ecology studies. However, the genome of Cocconeis spp. has not been sequenced. Consequently, their low-level molecular identification is currently impossible, besides a few examples. To address this gap, a polyphasic identification of C. neothumensis has been employed, combining ultra-morphological data with DNA barcoding markers. A strain of diatoms was isolated from P. oceanica leaves. It has been cultured in the laboratory and examined under Scanning Electron Microscopy (SEM). The 18S ribosomal RNA gene (18S rRNA, nrDNA) and the ribulose 1,5-biphosphate carboxylase (rbcL, cpDNA) gene were analysed for DNA barcoding characterisation. Since ultra-morphology data unambiguously identified the isolated strain as C. neothumensis Krammer, 1991, the molecular sequences herein reported will facilitate its rapid and accurate identification. In addition, our comparative analyses will facilitate the evaluation of these molecular markers for identification of closely related benthic diatoms. [ABSTRACT FROM AUTHOR]

Phaeodactylum tricornutum is considered a potential lipid production platform due to its high growth rates and elevated natural neutral lipid and polyunsaturated fatty acid (PUFA) contents. Furthermore, microalgae are emerging as promising sources of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). In this study, phosphomolybdic acid (PMo12), as a photocatalyst, can enhance the synthesis of neutral lipids and PUFAs by influencing the expression of lipid metabolism-related genes and photosynthesis in P. tricornutum. We also observed the contents of EPA and PUFA in engineered microalgae nearly doubled compared to the wild type, while neutral lipid content showed a significant increase of 69.7% in engineered microalgae. Notably, the growth rate of engineered microalgae remained comparable to that of the wild type. This work presents an effective approach to enhance the production of microalgal bioproducts, suggesting that photocatalysts such as PMo12 could serve as viable alternatives to genetic engineering technology, facilitating the commercialization of microalgal biodiesel. [ABSTRACT FROM AUTHOR]

• Diatoms shaped by Si enrichment or low salinity accumulated more Cd and Cu. • Si-enriched cells under low salinity showed the highest instantaneous metal influx. • The adsorption capacity of diatoms is mediated by cell wall physicochemical traits. • Lower Si availability and salinity led to rougher cell walls with larger surface area. • Higher silicification level decreased cell surface potential with more silanol groups. Increasing nitrogen and phosphorus discharge and decreasing sediment input have made silicon (Si) a limiting element for diatoms in estuaries. Disturbances in nutrient structure and salinity fluctuation can greatly affect metal uptake by estuarine diatoms. However, the combined effects of Si and salinity on metal accumulation in these diatoms have not been evaluated. In this study, we aimed to investigate how salinity and Si availability combine to influence the adsorption of metals by a widely distributed diatom Phaeodactylum tricornutum. Our data indicate that replete Si and low salinity in seawater can enhance cadmium and copper adsorption onto the diatom surface. At the single-cell level, surface potential was a dominant factor determining metal adsorption, while surface roughness also contributed to the higher metal loading capacity at lower salinities. Using a combination of non-invasive micro-test technology, atomic force microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy, we demonstrate that the diversity and abundance of the functional groups embedded in diatom cell walls vary with salinity and Si supply. This results in a change in the cell surface potential and transient metal influx. Our study provides novel mechanisms to explain the highly variable metal adsorption capacity of a model estuarine diatom. [Display omitted] [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the combined effects of temperature and light on the photosynthetic parameters and lipid accumulation in the diatom Phaeodactylum tricornutum, a model organism widely used for studies on diatom physiology, ecology, and biotechnology. Our results highlight the importance of the interaction between temperature and light intensity in influencing growth rates, pigments and active photosystems content, photosynthetic efficiency, lipid production and fatty acid composition in P. tricornutum. Measurements of the maximum electron transport rate (rETRmax) and rETR at maximum PAR (830 µmol m−2 s−1) confirmed that P. tricornutum exhibits significantly higher light sensitivity as growth temperature increases under light/dark cycles at two light intensities (25–60 µmol m−2 s−1). However, this trend was reversed under continuous light (25 µmol m−2 s−1). Moreover, higher rETRmax values (up to double) were observed at higher irradiance, either in intensity or under continuous light regimes, at the two temperatures tested. On the other hand, increasing light intensity amplified the observed effect of temperature on photosystem I (PSI) activity under light/dark regimes, but not under continuous light conditions. This resulted in a greater deficiency in PSI activity, likely due to limitations in electron supply to this photosystem. Furthermore, increasing the culture temperature from 20 °C to 25 °C triggered an increase in the number and size of cytoplasmic lipid droplets under conditions of increased light intensity, with an even more pronounced effect under continuous illumination. Notably, the combination of 25 °C and continuous illumination resulted in a more than twofold increase in triacylglyceride (TAG) content, reaching approximately 17 mg L−1. This condition also caused a substantial rise (up to ≈90%) in the proportions of palmitoleic and palmitic acids in the TAG fatty acid profile. [ABSTRACT FROM AUTHOR]

Autonomously replicating sequences (ARSs) are important accessories in episomal vectors that allow them to be replicated and stably maintained within transformants. Despite their importance, no information on ARSs in diatoms has been reported. Therefore, we attempted to identify ARS candidates in the model diatom, Phaeodactylum tricornutum, via chromatin immunoprecipitation sequencing. In this study, subunits of the origin recognition complex (ORC), ORC2 and ORC4, were used to screen for ARS candidates. ORC2 and ORC4 bound to 355 sites on the P. tricornutum genome, of which 69 were constantly screened after multiple attempts. The screened ARS candidates had an AT-richness of approximately 50% (44.39–52.92%) and did not have conserved sequences. In addition, ARS candidates were distributed randomly but had a dense distribution pattern at several sites. Their positions tended to overlap with those of the genetic region (73.91%). Compared to the ARSs of several other eukaryotic organisms, the characteristics of the screened ARS candidates are complex. Thus, our findings suggest that the diatom has a distinct and unique native ARSs. [ABSTRACT FROM AUTHOR]

The marine diatom Phaeodactylum tricornutum is currently used for various industrial applications, including the pharmaceutical industry as a cost-effective cell biofactory to produce Biologics. Recent studies demonstrated that P. tricornutum can produce functional monoclonal antibodies, such application is currently limited by the production yield that hinders industrialization. Therefore, it is necessary to understand and control the cell biology of P. tricornutum to improve the Biologics production yield. Transcriptomic analyses have recently been used by the pharmaceutical industry to improve the production of Biologics in mammalian cells, especially Biologics titer and cell productivity. Hence, in the present work, we performed a meta-analysis of seven publicly available RNA-Seq datasets from different strains of P. tricornutum, for which the culture conditions were chosen as similar as possible. We analyzed the differential expression of genes that are involved in biological processes that are well known to potentially impact the bioproduction and critical quality attributes of Biologics. Therefore, the expression of genes involved in the N-glycan biosynthesis, protein export and secretion, protein quality control and proteasome, as well as those encoding proteases were analyzed and compared. The results pave the way towards optimizing Biologics production in P. tricornutum and highlight that the Pt4, Pt3 Ov and Pt8 strains seem to be the most promising P. tricornutum strains. [ABSTRACT FROM AUTHOR]

Background: Phaeodactylum tricornutum is a versatile marine microalga renowned for its high-value metabolite production, including omega-3 fatty acids and fucoxanthin, with emerging potential for integrated biorefinery approaches that encompass biofuel and bioproduct generation. Therefore, in this study we aimed to optimize the cultivation conditions for boosting biomass, lipid, and fucoxanthin production in P. tricornutum, focusing on the impacts of different nutrient ratios (nitrogen, phosphorus, silicate), glycerol supplementation, and light regimes. Results: Optimized medium (− 50%N%, + 50% P, Zero-Si, 2 g glycerol) under low-intensity blue light (100 μmol m⁻2 s⁻1) improved biomass to 1.6 g L⁻1, with lipid productivity reaching 539.25 mg g⁻1, while fucoxanthin increased to 20.44 mg g−1. Total saturated fatty acid (ΣSFA) content in the optimized culture increased approximately 2.4-fold compared to the control F/2 medium. This change in fatty acid composition led to improved biodiesel properties, including a higher cetane number (59.18 vs. 56.04) and lower iodine value (53.96 vs 88.99 g I2/100 g oil). The optimized conditions also altered the biodiesel characteristics, such as kinematic viscosity, cloud point, and higher heating value. Conclusion: Our optimization approach reveals the significant potential of P. tricornutum as a versatile microbial platform for biomass, lipid, and fucoxanthin production. The tailored cultivation strategy successfully enhanced biomass and lipid accumulation, with notable improvements in biodiesel properties through strategic nutrient and light regime manipulation. These findings demonstrate the critical role of precise cultivation conditions in optimizing microalgal metabolic performance for biotechnological applications. [ABSTRACT FROM AUTHOR]

This study presents characterisation of diatom's PtLPCAT1 (acyl-CoA: lysophosphatidylcholine acyltransferase) activity in phospholipid remodelling. In this research microsomal fractions of yeast Δale1 mutant overexpressing PtLPCAT1 were used as a source of the tested enzyme. In the assays evaluating remodelling of different phospholipids by PtLPCAT1 not modified microsomal fractions of the tested yeast were used. The enzyme most intensively remodelled fatty acid composition of microsomal phosphatidylcholine (PC), however, it was also able to remodel phosphatidylethanolamine (PE) and phosphatidic acid (PA). To study the ability of the tested enzyme to remodel PC molecules containing fatty acids from the VLC-PUFA biosynthetic pathway the tested microsomes were enriched biochemically with: sn-1-18:1-sn-2-18:3(n-3)-PC, sn-1-18:1-sn-2-18:3(n-6)-PC, sn-1-18:1-sn-2-18:4(n-3)-PC, sn-1-18:1-sn-2-20:4(n-3)-PC and sn-1-18:1-sn-2-20:5(n-3)-PC. Further on it was shown that PtLPCAT1 was able to remodel PC of such modified microsomes with higher intensity than PC of unmodified microsomes. The remodelling efficiency of PtLPCAT1 was affected also by fatty acid donors; the process was most efficient when acyl-CoAs with unsaturated fatty acids were in the assays. In comparative studies the properties of Arabidopsis AtLPCAT1 and yeast ALE1 were tested. Effect of the temperature and pH values on the remodelling activity of PtLPCAT1 was also examined. [ABSTRACT FROM AUTHOR]

The production of the secondary metabolite dimethylsulfoniopropionate (DMSP) by marine microalgae has a strong impact on the global sulfur cycle, as DMSP is the precursor of the climate active gas dimethylsulfide. Quantifying the impact of abiotic parameters on DMSP production is needed to accurately depict DMSP production in ecosystem models. In this study, we investigated if de novo production of DMSP was upregulated under short‐term elevated irradiance and ultraviolet A radiation (UVA‐R). We exposed high‐light and low‐light acclimated cultures of Emiliania huxleyi, Tetraselmis sp., Thalassiosira oceanica, and Phaeodactylum tricornutum to high irradiance and UVA‐R treatments and followed de novo DMSP production and carbon fixation. We show that combined photosynthetically active radiation and UVA‐R resulted in increased net photoinhibition rates, but decreased specific DMSP production and growth compared to non‐UVA‐R treatments for all species. Photoacclimation to high photosynthetically active radiation resulted in a decreased UVA‐R sensitivity and positively affected the DMSP‐to‐carbon concentration ratios within the cultures. We conclude that there is no active short‐term upregulation of DMSP production under elevated photosynthetically active radiation and UVA‐R. Instead, the production of DMSP in response to light‐stress is closely coupled to particulate organic carbon production in all cases. While the relatively high cellular concentrations of DMSP do not exclude a de facto antioxidant function, its production is likely regulated by other cellular processes, for example, an overflow mechanism. The data of this study aim to improve the mechanistic understanding of DMSP synthesis, as well as to quantify DMSP production rates in different marine phytoplankton species. [ABSTRACT FROM AUTHOR]

Brine shrimp Artemia is able to filter particulate substances non-selectively and continuously, and its filtration capacity is related to various environmental parameters as well as Artemia growth stage. In this study, the filter-feeding rate (FFR) of Artemia franciscana at different temperatures (20°C /25°C /30°C) and stocking densities (200/400/750/1000 ind./L at two earlier growth stages with the body length of 0.91 ± 0.05 mm and 1.53 ± 0.22 mm, respectively; 50/100/200 ind./L at two later growth stages with the body length of 4.72 ± 0.51 mm and 10.26 ± 0.46 mm, respectively) on three unicellular algae (Chlorella vulgaris, Porphyridium purpureum, Phaeodactylum tricornutum) and two sizes of polyethylene beads (30 μm and 50 μm) was determined at Artemia four growth stages. In total 144 combinations were tested. The results showed that the FFR was positively correlated with the ambient temperature and Artemia body length, while it was negatively correlated with the Artemia density and particle size. One way ANOVA analysis showed that ambient temperature, Artemia stocking density and particle size mostly had significant effects on FFR (P < 0.05). And the favorable filtration particle size of Artemia increased with its body length. The equation of FFR in function of temperature (T), Artemia body length (BL) and stocking density (SD), and particle size (PS) was obtained using multiple linear regression analysis: FFR = 0.487* BL + 0.067* T-0.01* SD-0.064* PS-1.508 (R2 = 0.513). Of these four variables, body length had the greatest effect on FFR, followed by ambient temperature, particle size and Artemia density. There were interactions among three factors (T, SD and PS) and the interactive degree varied with Artemia growth. The results of this study provide a valuable guidance for proper feeding in controlled Artemia production and standardization of feeding protocol for ecotoxicity and fundamental Artemia research. [ABSTRACT FROM AUTHOR]

SUMMARY: Algae such as diatoms and haptophytes have distinct photosynthetic pigments from plants, including a novel set of carotenoids. This includes a primary xanthophyll cycle comprised of diadinoxanthin and its de‐epoxidation product diatoxanthin that enables the switch between light harvesting and non‐photochemical quenching (NPQ)‐mediated dissipation of light energy. The enzyme responsible for the reversal of this cycle was previously unknown. Here, we identified zeaxanthin epoxidase 3 (ZEP3) from Phaeodactylum tricornutum as the candidate diatoxanthin epoxidase. Knocking out the ZEP3 gene caused a loss of rapidly reversible NPQ following saturating light exposure. This correlated with the maintenance of high concentrations of diatoxanthin during recovery in low light. Xanthophyll cycling and NPQ relaxation were restored via complementation of the wild‐type ZEP3 gene. The zep3 knockout strains showed reduced photosynthetic rates at higher light fluxes and reduced specific growth rate in variable light regimes, likely due to the mutant strains becoming locked in a light energy dissipation state. We were able to toggle the level of NPQ capacity in a time and dose dependent manner by placing the ZEP3 gene under the control of a β‐estradiol inducible promoter. Identification of this gene provides a deeper understanding of the diversification of photosynthetic control in algae compared to plants and suggests a potential target to improve the productivity of industrial‐scale cultures. Significance Statement: This work reveals the identify of the enzyme responsible for the deactivation of the xanthophyll cycle and photoprotection in diatoms. [ABSTRACT FROM AUTHOR]

The diatom Phaeodactylum tricornutum shows potential as a source for biofuel production because of its considerable lipid content. Fatty acid β-oxidation plays a critical role in lipid breakdown. However, we still have a limited understanding of the role of fatty acid β-oxidation in lipid content in this microalga. In our study, we utilized a CRISPR interference method to reduce the expression of enoyl-CoA hydratase (PtECH), which is involved in the hydration of trans-2-enoyl-CoA to produce 3-hydroxyacyl-CoA during the β-oxidation pathway. Using this method, we developed two transgenic lines, PtECH21 and PtECH1487, which resulted from interference at two different sites of the PtECH gene, respectively. RT-qPCR analysis confirmed that the mRNA levels of PtECH in both mutants were significantly lower compared to the wild type. Surprisingly, the lipid content of both mutants increased notably. Additionally, both knockdown mutants exhibited higher chlorophyll content and improved photosynthetic efficiency of the photosystem II compared to the wild type. This study introduces a new approach for enhancing lipid content in P. tricornutum and expands our knowledge of the functions of enoyl-CoA hydratase in microalgae.

Summary Marine microalgae demonstrate a notable capacity to adapt to high CO2 and warming in the context of global change. However, the dynamics of their evolutionary processes under simultaneous high CO₂ and warming conditions remain poorly understood. Here, we analyze the dynamics of evolution in experimental populations of a model marine diatom Phaeodactylum tricornutum. We conducted whole‐genome resequencing of populations under ambient, high‐CO2, warming and high CO2 + warming at 2‐yr intervals over a 4‐yr adaptation period. The common genes selected between 2‐ and 4‐yr adaptation were found to be involved in protein ubiquitination and degradation and the tricarboxylic acid (TCA) cycle, and were consistently selected regardless of the experimental conditions or adaptation duration. The unique genes selected only by 4‐yr adaptation function in respiration, fatty acid, and amino acid metabolism, facilitating adaptation to prolonged high CO2 with warming conditions. Corresponding changes at the metabolomic level, with significant alterations in metabolites abundances involved in these pathways, support the genomic findings. Our study, integrating genomic and metabolomic data, demonstrates that long‐term adaptation of microalgae to high CO2 and/or warming can be characterized by a complex and dynamic genetic process and may advance our understanding of microalgae adaptation to global change. [ABSTRACT FROM AUTHOR]

Introduction: Nanomaterials such as silver nanoparticles (AgNPs) have gained widespread application across various fields. However, the large-scale production and application of AgNPs have raised concerns about their distribution in the environment and potential pollution issues. Methods: This study investigates the toxic effects of AgNPs on the diatom Phaeodactylum tricornutum by employing electron microscopy for cellular observation, quantifying apoptotic cell numbers, and measuring antioxidant indicators. The research examines how varying concentrations of AgNPs induce stress in P. tricornutum and the specific mechanisms of the toxic effect. Results: The findings reveal that AgNPs induce apoptosis in P. tricornutum cells by triggering a mitochondria-mediated pathway, marked by a decrease in mitochondrial membrane potential and the activation of caspase enzymes. Additionally, AgNP exposure results in an overproduction of reactive oxygen species (ROS) within the algal cells, leading to lipid peroxidation of the cell membrane and a consequent increase in malondialdehyde (MDA) levels. This oxidative stress response induces the upregulation of antioxidant enzyme activities in an attempt to mitigate the excessive ROS. Discussion: ROS is identified as the primary factor responsible for inducing mitochondria-mediated apoptosis. The research results will provide a theoretical basis for understanding the toxic effects and mechanisms of AgNPs on marine microalgae. [ABSTRACT FROM AUTHOR]

Secondary metabolites play important physiological roles being bioactive as defences against other organisms, or attractive signals used for various purposes, including reproduction. Their production and the emission in the environment may be viewed as an adaptive feature subjected to evolutionary selection. They were demonstrated to be useful for applications in various biotechnological fields, such as pharmaceutical, nutraceutical and cosmeceutical. Sponges and microalgae, including diatoms, are the most promising sources of bioactive compounds from the sea. We aimed at detecting the ecotoxicological effects of crude extracts and fractions obtained from three marine sponges, Geodia cydonium, Haliclona (Halichoclona) vansoesti and Agelas oroides and two benthic diatoms, Nanofrustulum shiloi and Cylindrotheca closterium on model marine organisms. We tested their effects on the Mediterranean purple sea urchin, Paracentrotus lividus, and on two diatoms, Phaeodactylum tricornutum and Cylindrotheca closterium, chosen because they are considered standard indicators for assessment of ecological impacts. Our results showed that extracts and fractions from both sponges and diatoms may be harmful for model invertebrates. However, eggs appeared "protected" from sponge allelochemicals when still unfertilized. The majority of sponge fractions exhibited noticeable impacts during the post-fertilization treatments. In contrast, fractions from diatoms notably increased the rate of malformations compared to the control, both in pre- and post-fertilization treatments. [ABSTRACT FROM AUTHOR]

Background: Conjugation-based episome delivery is a highly efficient method used to transfer DNA into the diatom Phaeodactylum tricornutum, facilitating the production of recombinant proteins and high-value metabolites. However, previous reports have indicated phenotypic heterogeneity among individual cells from clonally propagated exconjugant cell lines, potentially affecting the stability of recombinant protein production in the diatom. Results: Here, we characterized the differences between subpopulations with distinct fluorescence intensity phenotypes derived from a single exconjugant colony of P. tricornutum expressing the enhanced green fluorescent protein (eGFP). We analyzed the expression cassette sequence integrity, plasmid copy number, and global gene expression. Our findings reveal that lower copy numbers and the deletion of the expression cassette in part of the population contributed to low transgene expression. Gene co-expression analysis identified a set of genes with similar expression pattern to eGFP including a gene encoding a putative Flp recombinase, which may be related to variations in fluorescence intensity. These genes thus present themselves as potential candidates for increasing recombinant proteins production in P. tricornutum episomal expression system. Conclusions: Overall, our study elucidates genetic and transcriptomic differences between distinct subpopulations in a clonally propagated culture, contributes to a better understanding of heterogeneity in diatom expression systems for synthetic biology applications. [ABSTRACT FROM AUTHOR]

Pyrenoids are subcompartments of algal chloroplasts that increase the efficiency of Rubisco-driven CO 2 fixation. Diatoms fix up to 20% of global CO 2 , but their pyrenoids remain poorly characterized. Here, we used in vivo photo-crosslinking to identify pyrenoid shell (PyShell) proteins, which we localized to the pyrenoid periphery of model pennate and centric diatoms, Phaeodactylum tricornutum and Thalassiosira pseudonana. In situ cryo-electron tomography revealed that pyrenoids of both diatom species are encased in a lattice-like protein sheath. Single-particle cryo-EM yielded a 2.4-Å-resolution structure of an in vitro TpPyShell1 lattice, which showed how protein subunits interlock. T. pseudonana TpPyShell1/2 knockout mutants had no PyShell sheath, altered pyrenoid morphology, and a high-CO 2 requiring phenotype, with reduced photosynthetic efficiency and impaired growth under standard atmospheric conditions. The structure and function of the diatom PyShell provide a molecular view of how CO 2 is assimilated in the ocean, a critical ecosystem undergoing rapid change. [Display omitted] • Identification of the PyShell, a protein sheath that surrounds diatom pyrenoids • Multiscale imaging of PyShell lattices from in situ architecture to in vitro structure • PyShell knockout disrupts pyrenoid morphology and function, impairing cell growth • The PyShell is widely conserved, enabling much of the ocean's CO 2 fixation Identification and characterization of a protein lattice around the pyrenoid compartments of diatoms reveals that these prolific marine algae evolved a distinct pyrenoid architecture to promote Rubisco's CO 2 -fixing activity. [ABSTRACT FROM AUTHOR]

Diatoms are responsible for 20% of global carbon dioxide fixation and have significant potential in various biotechnological and industrial applications. Recently, the pennate diatom Phaeodactylum tricornutum has emerged as a prominent platform organism for metabolic engineering and synthetic biology. The availability of its genome sequence has facilitated the development of new bioengineering tools. In this study, we used in silico analyses to identify sequences potentially encoding thrombin-like proteins, which are involved in recognizing and cleaving the thrombin sequence LVPRGS in P. tricornutum. Protein structure prediction and docking studies indicated a similar active site and ligand positioning compared to characterized human and bovine thrombin. The evidence and efficiency of the cleavage were determined in vivo using two fusion-protein constructs that included YFP to measure expression, protein accumulation, and cleavage. Western blot analysis revealed 50–100% cleavage between YFP and N-terminal fusion proteins. Our findings suggest the existence of a novel thrombin-like protease in P. tricornutum. This study advances the application of diatoms for the synthesis and production of complex proteins and enhances our understanding of the functional role of these putative thrombin sequences in diatom physiology. Key points: • Protein structure predictions reveal thrombin-like active sites in P. tricornutum. • Validated cleavage efficiency of thrombin-like protease on fusion proteins in vivo. • Study advances bioengineering tools for diatom-based biotechnological applications. [ABSTRACT FROM AUTHOR]

Alternatives to conventional chemical treatments for parasitic diseases in fish are needed. Microalgal‐sourced fatty acid ethyl esters (FAEEs) have shown an antiparasitic effect against Gyrodactylus turnbulli infection in guppies. Here, we tested a range of commercial FAEEs of various carbon chain lengths and unsaturation levels against two fish parasites. Guppies and barramundi infected with G. turnbulli and Trichodina sp., respectively, were used. The most effective FAEE, after excluding those toxic to fish, was ethyl laurate (12:0). For both parasites, the LD50 was 18.75 μM within 250 min of incubation. Ethyl eicosapentaenoate (20:5n3) was the next most effective FAEE against G. turnbulli, and dihomo‐γ‐linolenic acid ethyl ester (20:3n6) and ethyl α‐linolenate (18:3n3) were the next most effective against Trichodina sp. In addition, FAEEs prepared from the microalga Phaeodactylum tricornutum residue, after fucoxanthin extraction, were examined against Trichodina sp. infection in barramundi for the first time. LD85 and LD100 was achieved at 2.5 and 5 μL mL−1 of the FAEE preparation, respectively. In vivo, immersion of infected barramundi in 1.25 μL mL−1 of this preparation for 24 h reduced infection prevalence from 100% to 53% and was non‐toxic to fish. [ABSTRACT FROM AUTHOR]

Heat shock transcription factor (HSF) are essential regulators of heat shock protein (HSP) gene expression in plants and algae, contributing to their resilience against biotic and abiotic stresses. However, the localization, structure, phylogenetic relationship, and characteristics of PtHSF genes in microalgae, especially in diatom Phaeodactylum tricornutum, remain largely unexplored. This study presents a comprehensive analysis of the PtHSF gene family in P. tricornutum. A genome-wide analysis identified 68 PtHSF genes, which were classified into two distinct subfamilies: traditional and untraditional. Motif and structure analyses revealed evidence of multiple duplication events within the PtHSF gene family. Expression profiling revealed diurnal patterns, with 34 genes being downregulated during the light period and upregulated during the dark period, while 19 genes exhibited the opposite pattern. These findings suggest that PtHSF genes may have specialized functions during the diurnal cycle and play a crucial role in maintaining cellular homeostasis in response to various stresses. Notably, PtHSF16, 30, and 43 genes exhibited higher expression levels, suggesting their potential importance. This study provides a valuable foundation for future investigations into the specific functions of HSFs under different stress conditions and their regulatory mechanisms in P. tricornutum and other microalgae. [ABSTRACT FROM AUTHOR]

In our previous study, we demonstrated that the microalgae Phaeodactylum tricornutum can bioaccumulate bisphenol A analogues. Since this microalgae species is part of the diet of marine filter-feeding organisms, such as bivalves, in this study we tested the hypothesis that a diet based on exposed microalgae can exert negative effects on the clam Ruditapes philippinarum. Microalgae were exposed for 7 days to 300 ng/L of bisphenol AF (BPAF), bisphenol F (BPF), and bisphenol S (BPS), alone or as a mixture (MIX), to allow bioaccumulation. Microalgae were then supplied as food to bivalves. After 7 and 14 days of diet, the effects of exposed microalgae were evaluated on a battery of biomarkers measured in haemolymph/haemocytes, gills and digestive glands of clams. In addition, bioaccumulation of the three bisphenols was investigated in clams by UHPLC-HRMS. The results obtained demonstrated that total haemocyte count (THC) increased in clams following ingestion for 7 days of BPAF- and BPF-exposed microalgae, while BPS-exposed microalgae significantly reduced THC after 14 days of diet. MIX- and BPS-exposed microalgae increased haemocyte proliferation. The diet of exposed microalgae affected acid and alkaline phosphatase activity in clams, with an opposite response between haemolymph and haemocytes. Regarding antioxidants, an increase in catalase activity was observed in clams after ingestion of BPA analogue-exposed microalgae. The results also demonstrated marked oxidative stress in gills, the first tissue playing an important role in the feeding process. Oxidative damage was recorded in both the gills and digestive glands of clams fed BPA analogue-exposed microalgae. Alterations in epigenetic-involved enzyme activity were also found, demonstrating for the first time that BPA analogue-exposed food can alter epigenetic mechanisms in marine invertebrates. No bioaccumulation of BPA analogues was detected in clam soft tissues. Overall, this study demonstrated that a diet of BPA analogue-exposed microalgae can induce significant alterations of some important biological responses of R. philippinarum. To our knowledge, this is the first study demonstrating the effects of ingestion of BPA analogue-exposed microalgae in the clam R. philippinarum, suggesting a potential ecotoxicological risk for the marine food chain, at least at the first levels. [ABSTRACT FROM AUTHOR]

Organic carbon fixed in chloroplasts through the Calvin–Benson–Bassham Cycle can be diverted toward different metabolic fates, including cytoplasmic and mitochondrial respiration, gluconeogenesis, and synthesis of diverse plastid metabolites via the pyruvate hub. In plants, pyruvate is principally produced via cytoplasmic glycolysis, although a plastid-targeted lower glycolytic pathway is known to exist in non-photosynthetic tissue. Here, we characterized a lower plastid glycolysis–gluconeogenesis pathway enabling the direct interconversion of glyceraldehyde-3-phosphate and phospho-enol-pyruvate in diatoms, ecologically important marine algae distantly related to plants. We show that two reversible enzymes required to complete diatom plastid glycolysis–gluconeogenesis, Enolase and bis-phosphoglycerate mutase (PGAM), originated through duplications of mitochondria-targeted respiratory isoforms. Through CRISPR-Cas9 mutagenesis, integrative 'omic analyses, and measured kinetics of expressed enzymes in the diatom Phaeodactylum tricornutum, we present evidence that this pathway diverts plastid glyceraldehyde-3-phosphate into the pyruvate hub, and may also function in the gluconeogenic direction. Considering experimental data, we show that this pathway has different roles dependent in particular on day length and environmental temperature, and show that the cpEnolase and cpPGAM genes are expressed at elevated levels in high-latitude oceans where diatoms are abundant. Our data provide evolutionary, meta-genomic, and functional insights into a poorly understood yet evolutionarily recurrent plastid metabolic pathway. Environmental and experimental methods reveal the importance of plastid-targeted Enolase and bis-phosphoglycerate mutase enzymes to diatoms, marine algae that contribute to global primary production. [ABSTRACT FROM AUTHOR]

The model diatom Phaeodactylum tricornutum is considered a promising source of various high value bioproducts, and developing cultivation processes is crucial for its commercialization. Although mixotrophy and heterotrophy have been recommended as effective strategies for microalgal cultivation, previous studies on P. tricornutum have yielded conflicting results in terms of cultivating this microalga. To verify the capacity of this microalga utilizing external organic carbon, both heterotrophic and mixotrophic cultivation with varied carbon sources were performed using an axenic strain. The results demonstrate that glycerol was the only organic carbon that substantially stimulated the growth of P. tricornutum in the presence of light. Sodium acetate (NaAc) at low concentrations could also promote growth, while at high concentrations led to severe inhibition under mixotrophic conditions. The addition of glucose imposed no appreciable impact on either cell density or biomass concentration, confirming that P. tricornutum cannot metabolize external glucose. Subsequently, a comparative analysis between mixotrophy and autotrophy was performed to reveal the influences of glycerol on the cellular metabolism based on growth performances, biochemical compositions, and chlorophyll fluorescence parameters. Results also indicate that the addition of glycerol did not have detrimental effects on the capacity of either pigments biosynthesis or photosynthesis, but enhanced the saturated fatty acids and reduced the unsaturated fatty acids. [ABSTRACT FROM AUTHOR]

Microalgae are considered promising sustainable feedstocks for the production of food, food additives, feeds, chemicals and various high-value products. Marine microalgae Phaeodactylum tricornutum, Isochrysis galbana and Nitzschia laevis are rich in fucoxanthin, which is effective for weight loss and metabolic diseases. The selection of microalgae species with outstanding nutritional profiles is fundamental for novel foods development, and the nutritional value of P. tricornutum, I. galbana and N. laevis are not yet fully understood. Hence, this study investigates and analyzes the nutritional components of the microalgae by chromatography and mass spectrometry, to explore their nutritional and industrial application potential. The results indicate that the three microalgae possess high nutritional value. Among them, P. tricornutum shows significantly higher levels of proteins (43.29%) and amino acids, while I. galbana has the highest content of carbohydrates (25.40%) and lipids (10.95%). Notwithstanding that P. tricornutum and I. galbana have higher fucoxanthin contents, N. laevis achieves the highest fucoxanthin productivity (6.21 mg/L/day) and polyunsaturated fatty acids (PUFAs) productivity (26.13 mg/L/day) because of the competitive cell density (2.89 g/L) and the advantageous specific growth rate (0.42/day). Thus, compared with P. tricornutum and I. galbana, N. laevis is a more promising candidate for co-production of fucoxanthin and PUFAs. [ABSTRACT FROM AUTHOR]

Roles of different ecological classes of algal exometabolites in regulating microbial community composition are not well understood. Here, we identify exometabolites from the model diatom Phaeodactylum tricornutum and demonstrate their potential to influence bacterial abundances. We profiled exometabolites across a time course of axenic algal growth using liquid chromatography-tandem mass spectrometry. We then investigated growth of 12 bacterial isolates on individual-identified exometabolites. Lastly, we compared responses of a P. tricornutum-adapted enrichment community to additions of two contrasting metabolites: selective growth substrate 4-hydroxybenzoic acid and putative signaling/facilitator molecule lumichrome. We identified 50 P. tricornutum metabolites and found distinct temporal accumulation patterns. Two exometabolites (of 12 tested) supported growth of distinct subsets of bacterial isolates. While algal exudates and algal presence drove similar changes in community composition compared with controls, exogenous 4-hydroxybenzoic acid addition promoted increased abundances of taxa that utilized it in isolation, and also revealed the importance of factors relating to algal presence in regulating community composition. This work demonstrates that secretion of selective bacterial growth substrates represents one mechanism by which algal exometabolites can influence bacterial community composition and illustrates how the algal exometabolome has the potential to modulate bacterial communities as a function of algal growth.

Light and nitrogen availability are basic requirements for photosynthesis. Changing in light intensity and nitrogen concentration may require adaptive physiological and life process changes in phytoplankton cells. Our previous study demonstrated that two Thalassiosira species exhibited, respectively, distinctive physiological responses to light and nitrogen stresses. Transcriptomic analyses were employed to investigate the mechanisms behind the different physiological responses observed in two diatom species of the genus Thalassiosira. The results indicate that the congeneric species are different in their cellular responses to the same shifting light and nitrogen conditions. When conditions changed to high light with low nitrate (HLLN), the large-celled T. punctigera was photodamaged. Thus, the photosynthesis pathway and carbon fixation related genes were significantly down-regulated. In contrast, the small-celled T. pseudonana sacrificed cellular processes, especially amino acid metabolisms, to overcome the photodamage. When changing to high light with high nitrate (HLHN) conditions, the additional nitrogen appeared to compensate for the photodamage in the large-celled T. punctigera, with the tricarboxylic acid cycle (TCA cycle) and carbon fixation significantly boosted. Consequently, the growth rate of T. punctigera increased, which suggest that the larger-celled species is adapted for forming post-storm algal blooms. The impact of high light stress on the small-celled T. pseudonana was not mitigated by elevated nitrate levels, and photodamage persisted. [ABSTRACT FROM AUTHOR]

Although the diverse impacts of elevated dissolved CO2 and warming on organisms within various trophic levels in marine food webs are well documented, we have yet to explore the biological links across different levels of biological organization from primary producers to secondary producers on an evolutionary time scale in a high‐CO2 ocean. Here, we cultured a model marine diatom Phaeodactylum tricornutum (primary producer) in predicted future high‐CO2 and/or warming conditions for ~ 1250 d with an experimental evolution approach and then fed them to the clam Coelomactra antiquata (secondary producer). We present an in‐depth multi‐omics analysis along the methylome (primary producer)–transcriptome (primary producer)–metabolome (primary producer)–metabolome (secondary producer) continuum. Our results showed that the downregulated terpenoid backbone biosynthesis in the methylome and transcriptome lead to decreased pyruvate levels and upregulation of some pathways (such as phenylalanine metabolism) in the metabolome of the primary producer in the long‐term warming conditions. These changes in metabolomic profile in the primary producer were then transferred to the secondary producer, resulting in changes in abundance of some metabolites, such as decreases in pyruvate, and in pyruvaldhyde (also known as methylglyoxal), and increases in 2‐hydroxylamino‐4,6‐dinitrotoluene. Our study provides a new insight into the molecular mechanisms underlying the trophic transfer from primary to secondary producers in a future high‐CO2 ocean and may provide more accurate projections of marine ecosystem services and functions over the next century. [ABSTRACT FROM AUTHOR]

Marine water temperatures are increasing due to anthropogenic climate change, constituting a major threat to marine ecosystems. Diatoms are major marine primary producers, and as such, they are subjected to marine heat waves and rising ocean temperatures. Additionally, under low tide, diatoms are regularly exposed to high temperatures. However, physiological and epigenetic responses to long-term exposure to heat stress remain largely unknown in the diatom Phaeodactylum tricornutum. In this study, we investigated changes in cell morphology, photosynthesis, and H3K27me3 abundance (an epigenetic mark consisting of the tri-methylation of lysine 27 on histone H3) after moderate and elevated heat stresses. Mutants impaired in PtEZH—the enzyme depositing H3K27me3—presented reduced growth and moderate changes in their PSII quantum capacities. We observed shape changes for the three morphotypes of P. tricornutum (fusiform, oval, and triradiate) in response to heat stress. These changes were found to be under the control of PtEZH. Additionally, both moderate and elevated heat stresses modulated the expression of genes encoding proteins involved in photosynthesis. Finally, heat stress elicited a reduction of genome-wide H3K27me3 levels in the various morphotypes. Hence, we provided direct evidence of epigenetic control of the H3K27me3 mark in the responses of Phaeodactylum tricornutum to heat stress. [ABSTRACT FROM AUTHOR]

This paper presents the results of a toxicity assessment of marine sediments from Vostok Bay based on responses of three testing organisms: the diatom Phaeodactylum tricornutum (Bohlin, 1897), nauplii of the brine shrimp Artemia salina (Linnaeus, 1758), and embryos and larvae of the sand dollar Scaphechinus mirabilis (Agassiz, 1864). The A. salina nauplii survival test was the least sensitive, showing a weak response in only two samples. The results of the experiments using microalgae cells and sand dollar larvae correlated both with each other and with long-term environmental monitoring data, thus, confirming the high degree of sediment toxicity off the western coast of the bay (Gaydamak and Srednyaya Coves). [ABSTRACT FROM AUTHOR]

Dengue, caused by the dengue virus (DENV), is a global health threat transmitted by Aedes mosquitoes, resulting in 400 million cases annually. The disease ranges from mild to severe, with potential progression to hemorrhagic dengue. Current research is focused on natural antivirals due to challenges in vector control. This study evaluates the antiviral potential of peptides derived from the microalgae Phaeodactylum tricornutum, known for its bioactive compounds. Microalgae were cultivated under controlled conditions, followed by protein extraction and hydrolysis to produce four peptide fractions. These fractions were assessed for cytotoxicity via the MTT assay and antiviral activity against DENV serotype 2 using flow cytometry and plaque formation assays. The 10–30 kDa peptide fraction, at 150 and 300 μg/mL concentrations, demonstrated no cytotoxicity and significantly reduced the percentage of infected cells and viral titers. These findings suggest that peptides derived from Phaeodactylum tricornutum exhibit promising antiviral activity against dengue virus serotype 2, potentially contributing to developing new therapeutic approaches for dengue. [ABSTRACT FROM AUTHOR]

Microbial degradation represents an eco-friendly alternative to traditional physicochemical treatments in removing persistent and toxic environmental pollutants, including synthetic dyes (i.e., methylene blue, MB) employed in different industries. The exploitation of thermophilic bacilli, such as those isolated from the shallow hydrothermal vents of the Eolian Islands (Italy), could provide valuable resources for the treatment of warm, dye-containing wastewater. In this study, we evaluated the ability of preformed biofilms on polypropylene perforated balls (BBs) of fifteen thermophilic bacilli, to decolor, degrade, and detoxify MB in aqueous solutions. Among them, BBs of Bacillus licheniformis B3-15 and Bacillus sp. s7s-1 were able to decolorize MB more than 50% in saline solution (NaCl 2%), incubated in static conditions at 45 °C for 48 h. At optimized initial conditions (10 mg L−1 MB, pH 5.2 for B3-15 or pH 4 for s7s-1), the two strains enhanced their decolorization potential, reaching 96% and 67%, respectively. As indicated by ATR-FTIR spectroscopy, the treatment with BB B3-15 was the most efficient in degrading the Cl–C and –NH groups of MB. This degraded solution was 40% less toxic than undegraded MB, and it has no impact on the bioluminescence of Vibrio harveyi, nor the growth of the marine diatom Phaeodactylum tricornutum. Biofilm formed by strain B3-15 on polypropylene perforated balls could be proposed as a component of bioreactors in the treatment of warm, dye-containing wastewater to concomitantly remediate MB pollution and simultaneously counteract harmful effects in aquatic environments. [ABSTRACT FROM AUTHOR]

The silicifying peptide R5 (H‐SSKKSGSYSGSKGSKRRIL‐OH) derived from diatoms is extensively investigated, but the mechanism underlying silica synthesis by R5 or R5‐alike peptides is still poorly understood, limiting the design of silicifying peptides Herein, machine learning techniques are used to design peptides with silicifying functionality. Utilizing a comprehensive dataset of peptides and their corresponding silicification outcomes, a deep learning model based on antimicrobial peptide migration learning is created. This model exhibits the remarkable capability to accurately predict peptide sequences with a high potential for facilitating silica formation. A selection of artificially designed peptides can catalyze the biomimetic synthesis of nanosilica, some of which demonstrate better catalytic activity with a wider pH range and faster reaction rate compared with the peptide R5. Additionally, the designed peptide is used to wrap the model diatom Phaeodactylum tricornutum with nanosilica coatings, resulting in a significant enhancement in the UV resistance of cells. The new silicified peptides are highly significant for advancing the understanding of the silica synthesis mechanism in diatoms, and the encapsulation of P. tricornutum has potential benefits in the development of new biosensors. [ABSTRACT FROM AUTHOR]

Diatoms are major players in the global carbon cycle, and their metabolism is affected by ocean conditions. Understanding the impact of changing inorganic nutrients in the oceans on diatoms is crucial, given the changes in global carbon dioxide levels. Here, we present a genome-scale metabolic model (iMK1961) for Cylindrotheca closterium, an in silico resource to understand uncharacterized metabolic functions in this ubiquitous diatom. iMK1961 represents the largest diatom metabolic model to date, comprising 1961 open reading frames and 6718 reactions. With iMK1961, we identified the metabolic response signature to cope with drastic changes in growth conditions. Comparing model predictions with Tara Oceans transcriptomics data unraveled C. closterium's metabolism in situ. Unexpectedly, the diatom only grows photoautotrophically in 21% of the sunlit ocean samples, while the majority of the samples indicate a mixotrophic (71%) or, in some cases, even a heterotrophic (8%) lifestyle in the light. Our findings highlight C. closterium's metabolic flexibility and its potential role in global carbon cycling. [ABSTRACT FROM AUTHOR]

The use of microalgae as a food ingredient has been gaining attention in recent years due to its nutritional benefits. The main goals of this study were to (i) assess the nutritional potential of Chlorella vulgaris, Tetraselmis chuii, Microchloropsis gaditana, and Phaeodactylum tricornutum; (ii) evaluate their bioactive properties (antioxidant activity, total phenolic content, and α-amylase inhibitory activity) and (iii) assess the main volatile compounds composition. The protein content was considerably high (32–44 mg/100 g dw) for all the microalgae strains. The DPPH scavenging potential range was 14–25 mg Trolox/100 g dw (highest for T. chuii) and the ferric reducing power ability range was 13–67 µmol Trolox/dw (higher for T. chuii). The total phenolic content range was 2–7 mg of gallic acid equivalents/g dw, for M. gaditana and T. chuii, respectively, which was mainly due to the presence of catechin (1–9 µg/g dw), epicatechin (3–29 µg/g dw), and vanillic acid (1–14 µg/g dw). The ɑ-amylase inhibitory potential range was 26–42%. C. vulgaris was richer in chlorophyll a (18 mg/g dw), whilst T. chuii was particularly rich in chlorophyll b (29 mg/g dw). P. tricornutum showed the highest carotenoid content (4 mg/g dw). Aldehydes and alkanes were the major compounds identified in M. gaditana, whereas alcohols and N-based compounds existed in higher amounts in P. tricornutum. T. chuii and C. vulgaris were enriched in ketones and alkenes. This study's novelty lies in its comprehensive and integrative analysis of the nutritional, bioactive, and volatile properties of four distinct microalgae strains. By providing detailed comparisons and highlighting potential applications in functional foods, it offers a unique contribution to the field of microalgae research and its practical application in the food industry. This multifaceted approach sets it apart from existing studies, offering new insights and opportunities for leveraging microalgae as valuable food ingredients. [ABSTRACT FROM AUTHOR]

The diatom Phaeodactylum tricornutum, known for its high triacylglycerol (TAG) content and significant levels of n-3 long chain polyunsaturated fatty acids (LC-PUFAs), such as eicosapentaenoic acid (EPA), has a limited ability to utilize exogenous organic matter. This study investigates the enhancement of acetate utilization in P. tricornutum by introducing an exogenous acetate transport protein. The acetate transporter gene ADY2 from Saccharomyces cerevisiae endowed the organism with the capability to assimilate acetate and accelerating its growth. The transformants exhibited superior growth rates at an optimal NaAc concentration of 0.01 M, with a 1.7- to 2.0-fold increase compared to the wild-type. The analysis of pigments and photosynthetic activities demonstrated a decline in photosynthetic efficiency and maximum electron transport rate. This decline is speculated to result from the over-reduction of the electron transport components between photosystems due to acetate utilization. Furthermore, the study assessed the impact of acetate on the crude lipid content and fatty acid composition, revealing an increase in the crude lipid content and alterations in fatty acid profiles, particularly an increase in C16:1n-7 at the expense of EPA and a decrease in the unsaturation index. The findings provide insights into guiding the biomass and biologically active products production of P. tricornutum through metabolic engineering. [ABSTRACT FROM AUTHOR]

In order to explore the effect of chemical modification on the inhibitory effect of intracellular polysaccharides of Phaeodactylum tricornutum (PTP) on the proliferation of cervical cancer Hela cells, in this study, the PTP was extracted by the ultrasound-assisted wall-breaking method combined with the hot water extraction method. Four types of chemical modification (sulfation modification, phosphorylation modification, acetylation modification and carboxymethylation modification ) were carried out on the PTP. The inhibitory effects of the initial PTP, sulfated polysaccharide (S-PTP), phosphorylated polysaccharide (P-PTP), acetylated polysaccharide (A-PTP) and carboxymethylated polysaccharide (C-PTP) on the proliferation of cervical cancer Hela cells were studied. The results showed that the degree of substitution of the S-PTP was 0.714, and the inhibitory effect of S-PTP on the proliferation rate of Hela cells could be up to 9.22% higher than that of PTP. The degree of substitution of P-PTP was 0.191, and the inhibitory effect of P-PTP on the proliferation rate of Hela cells could be up to 4.01% higher than that of PTP. The degree of substitution of acetylated polysaccharide A-PTP was 0.513, and the inhibitory effect of P-PTP on the proliferation rate of Hela cells could be up to 13.53% higher than that of PTP. The degree of substitution of C-PTP was 0.915, and the inhibitory effect of C-PTP on the proliferation rate of Hela cells could be up to 8.39% higher than that of PTP. The results showed that the inhibitory effects of four modified polysaccharides on the proliferation of Hela cells were all greater than that of PTP. Acetylation modification had the greatest inhibitory effect on the proliferation of Hela cells. Compared with PTP, the inhibitory effect of A-PTP against the proliferation rate of cervical cancer Hela cells was increased by 13.53%, reaching 46.05%. Through the experiments of chemical modification of PTP, it was proven that the introduction of a new chemical group into the molecular structure of PTP can lead to a great influence on the inhibition of cervical cancer cell proliferation. This result provides an important reference for further study on the biological activity of Phaeodactylum tricornutum and an experimental basis for subsequent drug research and development. [ABSTRACT FROM AUTHOR]

This work presents a low-cost, open-source turbidimeter, the 'Erlenmeter', designed to monitor the growth of microorganisms in batch cultures. It is easy to build, based exclusively on inexpensive off-the-shelf electronic components and 3D-printed parts. The Erlenmeter allows measuring the optical density of cultures on standard Erlenmeyer flasks without the need to open the flasks to collect aliquots, ensuring speed, minimal use of consumables, and elimination of the risk of contamination. These features make it particularly well-suited not just for routine research assays but also for experimental teaching. Here we illustrate the use of the Erlenmeter turbidimeter to record the growth of the microalga Phaeodactylum tricornutum, of the bacterium Escherichia coli, and of the yeast Saccharomyces cerevisiae, model organisms that are widely used in research and teaching. The Erlenmeter allows a detailed characterization of the growth curves of all organisms, confirming its usefulness for studying microbial populations dynamics both for research purposes and in classroom settings. [ABSTRACT FROM AUTHOR]

Each spring, the North Atlantic experiences one of the largest open‐ocean phytoplankton blooms in the global ocean. Diatoms often dominate the initial phase of the bloom with succession driven by exhaustion of silicic acid. The North Atlantic was sampled over 3.5 weeks in spring 2021 following the demise of the main diatom bloom, allowing mechanisms that sustain continued diatom contributions to be examined. Diatom biomass was initially relatively high with biogenic silica concentrations up to 2.25 μmol Si L−1. A low initial silicic acid concentration of 0.1–0.3 μM imposed severe Si limitation of silica production and likely limited the diatom growth rate. Four storms over the next 3.5 weeks entrained silicic acid into the mixed layer, relieving growth limitation, but uptake limitation persisted. Silica production was modest and dominated by the >5.0 μm size fraction although specific rates were highest in the 0.6–5.0 μm size fraction over most of the cruise. Silica dissolution averaged 68% of silica production. The resupply of silicic acid via storm entrainment and silica dissolution supported a cumulative post‐bloom silica production that was 32% of that estimated during the main bloom event. Diatoms contributed significantly to new and to primary production after the initial bloom, possibly dominating both. Diatom contribution to organic‐carbon export was also significant at 40%–70%. Thus, diatoms can significantly contribute to regional biogeochemistry following initial silicic acid depletion, but that contribution relies on physical processes that resupply the nutrient to surface waters. Plain Language Summary: Each spring, one of the largest phytoplankton blooms in the global ocean occurs in the North Atlantic Ocean. One group of phytoplankton, the diatoms, often dominates the early bloom. Diatoms are unique among the phytoplankton as they require the element silicon to construct their cell walls. Dissolved silicon is in relatively short supply in the North Atlantic, prompting this study of how the availability of silicic acid controls the contribution of diatoms to the bloom. At the start of our expedition, extremely low silicic acid concentrations in surface waters indicated that a diatom bloom had already occurred. Experiments revealed strong silicon limitation of the remaining diatoms. A series of four storms over 3 weeks introduced pulses of silicic acid to surface waters partially alleviating Si limitation. As a result, diatoms were able to significantly contribute to primary productivity and to the export of organic carbon despite persistent silicon limitation. The results indicate that diatoms can play a significant biogeochemical role in the North Atlantic bloom following the initial depletion of silicic acid, but their contribution is regulated by physical processes that resupply the nutrient to surface waters. Such processes may enhance overall bloom productivity and its contribution to carbon sequestration. Key Points: The diatom phase of the North Atlantic spring bloom terminated due to silicon limitationPhysical processes that reintroduced silicic acid sustained post‐bloom diatom net productivityThe resupply of silicic acid allowed Si‐limited diatoms to contribute significantly to primary production and to organic carbon export [ABSTRACT FROM AUTHOR]