Coccolith dissolution in the water column is an important process in the marine carbon cycle. Identifying dissolution in water column samples has been difficult due to a lack of experimental reference datasets showing dissolution morphologies. We conducted a laboratory CaCO3 dissolution experiment to detect differential dissolution morphologies of three selected coccolithophore (abundant marine calcareous phytoplankton) species, Coccolithus braarudii, Helicosphaera carteri, and Scyphosphaera apsteinii. These species were selected because they are ecologically and biogeochemically important (significant contributors to CaCO3 production) and have been less studied than Gephyrocapsa. Muroliths of S. apsteinii dissolve faster than lopadoliths, which in turn dissolve as fast as H. carteri but faster than C. braarudii. In S. apsteinii lopadoliths, dissolution rate depends on the crystallographic orientation of the crystals. Comparison with field samples shows that experimental data are helpful when interpreting field samples. For example, we identify dissolution in water and sediment samples reported in the literature. In C. braarudii dissolution reveals a nanostructure on the proximal side of the distal shield, an observation that has implications for coccolith biomineralization models, which do not currently account for the formation of such a structure. This nanostructure features "units" of ca. 50-100 nm and resembles the nanostructure well known from extracellular calcifiers such as molluscs and foraminifera. Whether this resemblance is underpinned by a similar formation mechanism remains unknown, but we think this unlikely.

Germplasm banks are important for preserving genetic diversity, yet the availability and long-term maintenance of macroalgal strains in germplasm banks is currently limited in European collections. To support future food security, restoration efforts, and biotechnological innovation, a strategy was recently developed for the long-term preservation of macroalgal genetic diversity. A foundational step in this effort is to assess the existing biodiversity, biogeographical distribution, and commercial relevance of seaweed cultures maintained in European collections. Using a universal data-collection template distributed widely across European seaweed networks, we compiled and analysed information on these seaweed cultures. As of November 2025, the resulting SeaStrains Database of European Seaweed Collections contains 2541 cultures representing 426 species, accounting for only 4

The wide geographic distribution of microorganisms, combined with their vast taxonomic and functional diversity, make them indispensable reservoirs of genetic variation that sustain ecosystem resilience and fuel biotechnological innovation. However, to use this diversity, microbiologists must navigate a complex legal and regulatory landscape governed by multiple United Nations treaties and their respective access and benefit-sharing frameworks as well as regulatory frameworks specific to particular ecosystems, biosecurity, pathogens, and intellectual property. This complex regulatory web is also actively growing and changing, which makes it immensely challenging for a "regular" microbiologist to navigate. For policymakers and negotiators, it is also difficult to appreciate the full complexity that practitioners experience. This policy briefing provides a concise regulatory guide for practitioners and policymakers alike, summarized in a graphical overview, to provide more clarity and understanding for those at the edge of decision-making and practice.

Phaeocystales, comprising the genus Phaeocystis and an uncharacterized sister lineage, are nanoplanktonic haptophytes widespread in the global ocean. Several species form mucilaginous colonies and influence key biogeochemical cycles, yet their underlying diversity and ecological strategies remain underexplored. Here, we present new genomic data from 13 strains, including three high-quality reference genomes (N50 > 30 kbp), and integrate previous metagenome-assembled genomes to resolve a robust phylogeny. Divergence timing of P. antarctica aligns with Miocene cooling and Southern Ocean isolation. Genomic traits reveal metabolic flexibility, including mixotrophic nitrogen acquisition in temperate waters and gene expansions linked to polar nutrient adaptation. Concordantly, transcriptomic comparisons between temperate and polar Phaeocystis suggest Southern Ocean populations experience iron and B12 limitation. We also identify signatures of horizontal gene transfer and endogenous giant virus/virophage insertions. Together, these findings highlight Phaeocystales as an ecologically versatile and geographically widespread lineage shaped by evolutionary innovation and adaptation to contrasting environmental stressors.

The cycling of calcium carbonate (CaCO3) in the ocean is closely linked to seawater alkalinity and the regulation of atmospheric CO2. In the modern pelagic ocean, almost all CaCO3 is produced by three groups of calcifying planktonic organisms: coccolithophores, foraminifers, and shelled pteropods. In this Review, we examine the differences in functional traits that define each group's distinctive role in the global carbon cycle and their sensitivity to climate change and ocean acidification. This synthesis reveals that a single representation of CaCO3 in climate models is unlikely to accurately reflect system dynamics or their impacts on biogeochemical cycling under climate change. We argue that understanding past and future CaCO3 cycle requires a better delineation of the traits that make up the diversity of calcifying plankton groups.

Abstract. We conducted a laboratory CaCO3 dissolution experiment to detect differential dissolution morphologies of three selected coccolithophore (abundant marine calcareous phytoplankton) species, Coccolithus braarudii, Helicosphaera carteri, and Scyphosphaera apsteinii. These species were selected because they are ecologically and biogeochemically important (significant contributors to CaCO3 production) and have been less studied than Gephyrocapsa. Muroliths of S. apsteinii dissolve faster than lopadoliths, which in turn dissolve as fast as H. carteri but faster than C. braarudii. Lopadolith R-units dissolve faster than V-units. Comparison with field samples shows that experimental data are helpful when interpreting field samples. For example, we identify dissolution in water and sediment samples reported in the literature. In C. braarudii dissolution reveals a nanostructure on the proximal side of the distal shield, an observation that has implications for coccolith biomineralization models, which do not currently account for the formation of such a structure.

Microbial eukaryotes remain understudied despite their critical ecological importance, with the exception of a few established models. They are often small, difficult to culture, and resistant to standard labeling and imaging techniques. Here, we use ultrastructure expansion microscopy (U-ExM) to carry out high-resolution volumetric imaging of over 200 cultured planktonic eukaryotes across major lineages. By combining U-ExM with pan- and specific immuno-labeling, we reveal microtubule and centrin-containing elements and assign molecular identities to enigmatic cytoskeletal structures observed previously only by electron microscopy. This comprehensive resource provides a basis for understanding cytoskeletal diversity, phenotypic plasticity, and evolutionary dynamics. Moreover, our approach extends to mixed environmental samples, paving the way for environmental cell biology at ultrastructural resolution-a crucial step toward understanding and protecting ecosystems in the face of accelerating biodiversity loss.

Ceratocorys armata, C. gourretii, and C. horrida have historically been treated as distinct species based on morphology. Both field samples and cultured strains, however, exhibit continuous morphological variation and intergradations between these taxa. Here, strains from Viet Nam, Japan (Pacific Ocean), and France (Mediterranean Sea, Atlantic Ocean) were analyzed using integrated morphomolecular approaches. Cultured strains revealed morphological intergradations from C. horrida to C. armata and from C. armata to C. gourretii. Phylogenetic analysis based on the ITS1-5.8S-ITS2 rDNA region sequences and the SSU (18S) and LSU (28S) nuclear rDNA gene sequences confirmed the genetic identity of these three taxa for these markers. The ITS2 secondary structure comparisons-including C. malayensis from Viet Nam and Malaysia-further supported their conspecificity, while validating C. malayensis as a distinct species. Based on these data, we have proposed to treat them as formae: C. horrida f. horrida, C. horrida f. armata, and C. horrida f. gourretii. Furthermore, our results indicated that C. malayensis strains from Viet Nam are non-toxic. We have also provided morphological descriptions and illustrations of C. bipes and C. magna, two species rarely reported in the Asia-Pacific region, enhancing the taxonomic clarity of the genus.

Photosynthetic microbial eukaryotes play a pivotal role as primary producers in the Arctic Ocean, where seasonal blooms within and below the ice are crucial phenomena, contributing significantly to global primary production and biogeochemical cycling. In this study, we investigated the taxonomic composition of sympagic algae and phytoplankton communities during the Arctic under-ice spring bloom using metabarcoding of the 18S rRNA gene. Samples were obtained from three size fractions over a period of nearly three months at an ice camp deployed on landfast ice off the coast of Baffin Island as part of the Green Edge project. We classified the major sympagic and phytoplankton taxa found in this study into biogeographical categories using publicly available metabarcoding data from more than 2800 oceanic and coastal marine samples. This study demonstrated the temporal succession of taxonomic groups during the development of the under-ice bloom, illustrated by an overall transition from polar to polar-temperate taxa, particularly in the smallest size fraction. Overlooked classes such as Pelagophyceae (genera Plocamiomonas and Ankylochrysis), Bolidophyceae (Parmales environmental clade 2), and Cryptophyceae (Baffinella frigidus) might play a greater role than anticipated within the pico-sized communities in and under the ice pack during the pre-bloom period. Finally, we emphasize the importance of microdiversity, taking the example of B. frigidus, for which two ecotypes linked to pelagic and sea ice environments have been identified.

ABSTRACT Cyanate (OCN−) is an organic nitrogen compound found in aquatic environments potentially involved in phytoplankton growth. Given the prevalence and activity of cyanate lyase genes in eukaryotic microalgae, cyanate has been suggested as an alternative source of nitrogen in the environment. However, the conditions under which cyanate lyase is expressed and the actual capacity of microalgae to assimilate cyanate remain largely underexplored. Here, we studied the nitrogen metabolism in the cosmopolitan open-ocean picoalga Pelagomonas calceolata (Pelagophyceae and Stramenopiles) in environmental metatranscriptomes and transcriptomes from culture experiments under different nitrogen sources and concentrations. We observed that cyanate lyase is upregulated in nitrate-poor oceanic regions, suggesting that cyanate is an important molecule contributing to the persistence of P. calceolata in oligotrophic environments. Non-axenic cultures of P. calceolata were capable of growing on various nitrogen sources, including nitrate, urea, and cyanate, but not ammonium. RNA sequencing of these cultures revealed that cyanate lyase was downregulated in the presence of cyanate, indicating that this gene is not involved in the catabolism of extracellular cyanate to ammonia. Based on environmental data sets and laboratory experiments, we propose that cyanate lyase is important in nitrate-poor environments to generate ammonia from cyanate produced by endogenous nitrogenous compound recycling rather than being used to metabolize imported extracellular cyanate as an alternative nitrogen source.IMPORTANCEVast oceanic regions are nutrient-poor, yet several microalgae thrive in these environments. While various acclimation strategies to these conditions have been discovered in a limited number of model microalgae, many important lineages remain understudied. Investigating nitrogen metabolism across different microalga lineages is crucial for understanding ecosystem functioning in low-nitrate areas, especially in the context of global ocean warming. This study describes the nitrogen metabolism of Pelagomonas calceolata, an abundant ochrophyte in temperate and tropical oceans. By utilizing both global scale in situ metatranscriptomes and laboratory-based transcriptomics, we uncover how P. calceolata adapts to low-nitrate conditions. Our findings reveal that P. calceolata can metabolize various nitrogenous compounds and relies on cyanate lyase to recycle endogenous nitrogen in low-nitrate conditions. This result paves the way for future investigations into the significance of cyanate metabolism within oceanic trophic webs.

Cryptophytes are abundant and ubiquitous microalgae that constitute a major plastid source for kleptoplastidic ciliates and dinoflagellates. Despite their ecological significance, the understanding of their light preferences and photophysiology remains limited. Here, we provide a comprehensive study of the response of the haploid strain Teleaulax amphioxeia (Cr10EHU) to varying light irradiance. This strain is capable of growing under a wide range of irradiance levels, notably by finely tuning the different pigments bound to the membrane light-harvesting proteins. Analysis of the luminal phycoerythrin content revealed remarkable flexibility, with phycoerythrin emerging as a pivotal protein facilitating acclimation to varying light levels. Detailed ultrastructure examinations unveiled that this adaptability was supported by the synthesis of large thylakoidal vesicles, likely enhancing the capture of green photons efficiently under low light, a phenomenon previously undocumented. Teleaulax amphioxeia Cr10EHU effectively regulated light utilization by using a cryptophyte state transition-like process, with a larger amplitude observed under high growth irradiance. Furthermore, our results revealed the establishment of growth irradiance-dependent non-photochemical quenching of fluorescence, likely inducing the dissipation of excess light. This study underscores the particularities and the significant photoadaptability of the plastid of the haploid form of T. amphioxeia. It constitutes a comprehensive photophysiological characterization of the Cr10EHU strain that paves the way for future studies of the kleptoplastidy process.

Dinophysis dinoflagellates are predators of Mesodinium ciliates, from which they retain only the plastids of cryptophyte origin. The absence of nuclear photosynthetic cryptophyte genes in Dinophysis raises intriguing physiological and evolutionary questions regarding the functional dynamics of these temporary kleptoplastids within a foreign cellular environment. In an experimental setup including two light conditions, the comparative analysis with Mesodinium rubrum and the cryptophyte Teleaulax amphioxeia revealed that Dinophysis acuminata possessed a smaller and less dynamic functional photosynthetic antenna for green light, a function performed by phycoerythrin. We showed that the lack of the cryptophyte nucleus prevented the synthesis of the phycoerythrin α subunit, thereby hindering the formation of a complete phycoerythrin in Dinophysis. In particular, biochemical analyses showed that Dinophysis acuminata synthesized a poorly stable, incomplete phycoerythrin composed of chromophorylated β subunits, with impaired performance. We show that, consequently, a continuous supply of new plastids is crucial for growth and effective photoacclimation in this organism. Transcriptome analyses revealed that all examined strains of Dinophysis spp. have acquired the cryptophyte pebA and pebB genes through horizontal gene transfer, suggesting a potential ability to synthesize the phycobilin pigments bound to the cryptophyte phycoerythrin. By emphasizing that a potential long-term acquisition of the cryptophyte plastid relies on establishing genetic independence for essential functions such as light harvesting, this study highlights the intricate molecular challenges inherent in the enslavement of organelles and the processes involved in the diversification of photosynthetic organisms through endosymbiosis.

The eDNAqua-Plan project stands as a beacon of innovation in the biomonitoring of marine and freshwater ecosystems, propelled by the urgent need to integrate DNA-based approaches in aquatic bioassessment and monitoring frameworks. The broad utilisation of cutting-edge environmental DNA (eDNA) and DNA barcoding methodologies is dependent on complete, reliable, and accessible reference DNA sequence data (Rimet et al. 2021). Complete and interoperable metadata is crucial to allow a broad reuse of (e)DNA data and analysis outputs, and for a broader uptake of results by end users. The eDNAqua-Plan project aims to address key limitations to the routine implementation of eDNA-based monitoring methods in Europe by developing plans for federated DNA barcode reference libraries and eDNA data repositories to support DNA-based environmental monitoring. This will ensure a sustainable and reliable infrastructure to underpin its broad use, thereby paving the way for more effective conservation and management strategies. The project is working towards creating a comprehensive overview of standardisation efforts and data workflows, through collaborations with other projects, initiatives and infrastructures for aquatic monitoring across the European Union (EU) and associated countries. We are analysing existing archives (e.g., International Nucleotide Sequence Database Collaboration (INSDC), Barcode of Life Data System (BOLD), Global Biodiversity Information Facility (GBIF), Ocean Biodiversity Information System (OBIS)), portals, and papers to determine current and best practices through the use of questionnaires, manual evaluation of repositories, and machine learning methods (LLMs). This includes an overview of the usage of existing metadata and data standards (e.g., Minimum Information about any (X) Sequence Specifications from the Genomics Standards Consortium (GSC), Darwin Core standard). The results are being integrated by a team of experts in marine and freshwater biomonitoring. With a diverse consortium comprising 18 partner institutions from 11 countries and one international institute, eDNAqua-Plan brings together experts in marine and freshwater monitoring, eDNA analysis, and data science. The collective effort by this consortium will lay the groundwork for the creation of a digital ecosystem of eDNA repositories and an integrated reference library of marine and freshwater species, adhering to FAIR (Findable, Accessible, Interoperable, and Reusable) principles.

Two new fusarochromanone derivatives, deacetylfusarochromene (1) and deacetamidofusarochrom-2′,3-diene (2), along with the previously reported metabolites fusarochromanone TDP-2 (3), fusarochromene (4), 2,2-dimethyl-5-amino-6-(2′E-ene-4′-hydroxylbutyryl)-4-chromone (5), fusarochromanone (6), (−)-chrysogine (7), and equisetin (8), were isolated from the marine fungus Fusarium equiseti UBOCC-A-117302. The structures of the compounds were determined by extensive spectrometric (HRMS) and spectroscopic (1D and 2D NMR) analyses, as well as specific rotation. Among them, 2 and 5 showed inhibition of three protein kinases with IC50 values ranging from 1.42 to 25.48 μM. Cytotoxicity and antimicrobial activity of all isolated compounds were also evaluated. Six fusarochromanone derivatives (1–6) exhibited diverse activities against three cell lines, RPE-1, HCT-116, and U2OS (IC50 values ranging from 0.058 to 84.380 μM). Equisetin (8) showed bactericidal activities against Bacillus cereus and Listeria monocytogenes (MBC values of 7.8 and 31.25 µM, respectively), and bacteriostatic activity against Enterococcus faecalis (MIC value of 31.25 µM). Compounds 2 and 4 showed bacteriostatic activities against Listeria monocytogenes (MIC of 125 µM).