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Povzetek: Diatom blooms influence carbon cycling through organic matter production and its deposition or remineralization – processes mediated by the microbial community. Viruses can influence diatom bloom dynamics and even terminate blooms, yet interactions between diatoms, their viruses, and associated bacteria remain poorly resolved. Here, we examined how infection of the toxigenic diatom Pseudo-nitzschia galaxiae by its ssRNA virus PnGalRNAV reshapes host physiology, microbiome structure, and organic-matter processing in non-axenic batch cultures. Using epi-fluorescence microscopy, 16S rRNA amplicon sequencing, and metatranscriptomics, we linked microbial composition, localisation, and functional activity during viral lysis. Infection rapidly collapsed diatom growth and induced a senescence-like host state, with broad repression of photosynthesis, silicon metabolism, and core biosynthetic pathways, alongside induction of heat-shock and other stress-related genes. Concurrently, phycosphere-associated bacteria declined, detritosphere-associated bacteria increased, and community composition shifted from Marinobacter (Gammaproteobacteria) dominated, towards Flavobacteriaceae (Bacteroidetes) dominated, especially by Polaribacter. In non-infected controls Alphaproteobacteria proved to benefit from the stable healthy phycospheres with a distinct DOM pool. Bacterial metatranscriptomes showed significant upregulation of polysaccharide-degradation-associated genes in infected cultures, indicating active utilisation of lysis-derived diatom glycans. Similar compositional and metabolic profiles in infected cultures and later-stage senescent controls suggest infection accelerated senescence-associated microbial processes. Overall, viral lysis converted a productive diatom culture into a detrital, DOM-rich environment that selects for specialised polysaccharide degraders, redirects carbon through the viral shunt and may accelerate nutrient recycling in coastal systems. Extending this approach to natural microbial communities and diverse diatom–virus systems will help determine whether these mechanisms are broadly conserved.
Ključne besede: diatoms, virus, bacteria, Pseudo-nitzschia, shunt, senescence, microbiome, phycosphere
Objavljeno v DiRROS: 10.08.2026; Ogledov: 208; Prenosov: 219
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Povzetek: Machine learning models provide a scalable approach for predicting the diversity of eukaryotic microbial plankton from environmental predictors. However, the extent to which these models generalize to data outside the training set remains poorly quantified. In this study, XGBoost was used to predict the 18S rRNA gene Shannon Diversity Index (SDI) from seven environmental predictors derived from satellite and model data. Surface samples were collected between 2001 and 2025 at two fixed stations in the northwestern Mediterranean (BBMO and SOLA), one fixed station in the northern Adriatic Sea (VIDA), and during the HOTMIX expedition, which sampled an east-west open-sea transect across the Mediterranean Sea. Model performance was assessed using standard repeated K-fold cross-validation (CV), Leave-One-Dataset-Out CV (LODO-CV), and a blocked spatiotemporal CV that combined LODO with temporal forward chaining. Under standard K-fold CV, the model showed moderate performance (R² = 0.44, RMSE = 0.59). In contrast, performance declined substantially under LODO-CV (R² = 0.09, RMSE = 0.73), with uniformly low per-dataset generalization, a pattern also observed with blocked spatiotemporal CV. VIDA and HOTMIX sampled environmental regimes distinct from those at BBMO and SOLA, which may partly explain their poor transferability. Additionally, BBMO and SOLA, despite similar environmental conditions, exhibited poor transferability, indicating that technical differences among independently collected 18S rRNA datasets likely constrain transferability, although their effects cannot be disentangled from environmental variation. Overall, these results highlight the limitations of imbalanced training data and underscore the importance of spatially explicit evaluation, protocol standardization, and environmentally representative coverage.
Ključne besede: cross-validation, data leakage, eukaryotic plankton, machine learning, marine biodiversity, Mediterranean Sea, omics, shannon diversity index
Objavljeno v DiRROS: 29.07.2026; Ogledov: 265; Prenosov: 149
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Povzetek: The mucilage phenomenon consists of the appearance of large gelatinous aggregates floating in the water column. In summer 2024, this event has reappeared in the Northern Adriatic Sea (NAS) on a large scale. This study provides an integrated characterization of the microalgal community within mucilage aggregates and surrounding waters in two NAS areas (Gulf of Trieste and Conero Riviera) using light microscopy (LM), metabarcoding (MB) based on ribosomal 18S V4 and V9 markers, and scanning electron microscopy (SEM) for selected taxa identification. Mucilage aggregates acted as dynamic microbial hotspots, hosting a rich diatom community, with abundances 1–2 orders of magnitude higher than in the surrounding water. Dominant diatom species were Cylindrotheca closterium, Nitzschia spp., Nitzschia gobbii, and Thalassionema nitzschioides. Some phytoflagellates (e.g., Tetraselmis spp.) and dinoflagellates (e.g., Karlodinium veneficum, Pseliodinium fusus, and Wangodinium sinense) were detected exclusively by MB, while LM and SEM revealed species missed by other approaches. Gonyaulax fragilis, one of the species indicated as an important mucus producer, was present at the onset and throughout the phenomenon, as detected by LM and MB. The integrated approach improves knowledge of microalgal communities in NAS mucilage.
Ključne besede: mucilage, Northern Adriatic Sea, phytoplankton, microalgae, metabarcoding, microscopy, Gonyaulax fragilis, Harmful Algal Blooms
Objavljeno v DiRROS: 27.01.2026; Ogledov: 701; Prenosov: 605
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Povzetek: The worldwide disruption caused by the beginning of the COVID-19 pandemic has dramatically impacted the activities of marine scientists working towards the goals of the UN Ocean Decade. As in other disciplines, marine early-career researchers (ECRs) are essential contributors to the development of novel and innovative science. Based on a survey of 322 of our peers, we show that the pandemic negatively impacted marine ECRs in ways that further exacerbate existing structural challenges such as social isolation, job insecurity, and short-term contracts, competitive funding, and work pressure. Furthermore, we find that the success and wellbeing of marine ECRs depends heavily on networking opportunities, gaining practical experience, collecting data, and producing publications, all of which were disrupted by the pandemic. Our analysis shows that those in the earliest stages of their careers feel most vulnerable to long-term career disadvantage as a result of the pandemic. This paper contributes to the empirical body of work about the impacts of the pandemic on marine science and offers recommendations on how marine ECRs should be supported to achieve the UN Ocean Decade’s goal of producing “the science we need for the ocean we want”.
Ključne besede: early career scientists, intersectional, institutional responses, marine science, reflexive science, SARS-CoV-2, UN Ocean Decade
Objavljeno v DiRROS: 12.03.2025; Ogledov: 1135; Prenosov: 1346
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Povzetek: Diatoms of the genus Pseudo-nitzschia H.Peragallo are known to produce domoic acid (DA), a toxin involved in amnesic shellfish poisoning (ASP). Strains of the same species are often classified as both toxic and nontoxic, and it is largely unknown whether this difference is also genetic. In the Northern Adriatic Sea, there are virtually no cases of ASP, but DA occasionally occurs in shellfish samples. So far, three species—P. delicatissima (Cleve) Heiden, P. multistriata (H. Takano) H. Takano, and P. calliantha Lundholm, Moestrup, & Hasle—have been identified as producers of DA in the Adriatic Sea. By means of enzme-linked immunosorbent assay (ELISA), high-performance liquid chromatography with UV and visible spectrum detection (HPLC-UV/VIS), and liquid chromatography with tandem mass spectrometry (LC-MS/MS), we reconfirmed the presence of DA in P. multistriata and P. delicatissima and detect for the first time in the Adriatic Sea DA in P. galaxiae Lundholm, & Moestrup. Furthermore, we attempted to answer the question of the distribution of DA production among Pseudo-nitzschia species and strains by sequencing the internal transcribed spacer (ITS) phylogenetic marker and the dabA DA biosynthesis gene and coupling this with toxicity data. Results show that all subclades of the Pseudo-nitzschia genus contain toxic species and that toxicity appears to be strain dependent, often with geographic partitioning. Amplification of dabA was successful only in toxic strains of P. multistriata and the presence of the genetic architecture for DA production in non-toxic strains was thus not confirmed.
Ključne besede: Adriatic, dabA, domoic acid, Pseudo-nitzschia galaxiae
Objavljeno v DiRROS: 16.07.2024; Ogledov: 1406; Prenosov: 898
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