Diatoms are among the most common epibionts and have been recorded on the surfaces of various living substrates, either plants or animals. However, said studies are still scarce in view of the many substrata available. In this study, epibiotic diatoms living on Callinectes bellicosus were identified for the first time from a subtropical coastal lagoon in northwest Mexico. We tested the null hypothesis that the diatom flora living on the shells of C. bellicosus would not be similar to that recorded for mangrove sediments, its typical habitat. The epibiotic diatoms were brushed off from the carapaces of two specimens, acid-cleaned, mounted in synthetic resin, and identified based on frustule morphology. In this way, 106 taxa from 45 genera were recorded, including 24 singletons, and six new records for the Mexican northwest region. The best-represented genera were Nitzschia (10 taxa), Mastogloia (9), Diploneis (7), Navicula (7), Amphora (5), Cocconeis (5), Tryblionella (4), and Gyrosigma (4). Species composition included 93% of local taxa, thus refuting the proposed hypothesis and supporting the alternate one. Although the estimated species richness was lower than in sediments, it deems the green crab carapace a favorable substrate for the growth of benthic diatoms.

Rivers are crucial hydrological cycle components, supporting ecosystems and human activities. Managing and protecting river water quality is essential. Diatoms, microscopic algae, are widespread and sensitive to changes in water quality, making them effective bioindicators. This study focused on the Kuils River in the Western Cape, South Africa, where diatom sampling was conducted at four sites. Their communities are affected by different physicochemical parameters, such as changes in pH, salinisation, eutrophication, and organic enrichment. A total of 98 diatom species were identified. The Omnidia software was used to calculate the Generic Diatom Index, Specific Pollution Index, and Trophic Diatom Index. Historical physicochemical data from the Department of Water and Sanitation provided a reference for comparing diatom communities. The results showed clear signs of pollution, as shifts in diatom species composition were observed. Pollu-tion-tolerant species like the Nitzchia palea, Navicula viridula, Eunotia bilunaris, and Fragilaria ulna dominated, while less pollution-tolerant species like Gomphonema parvulum and Cyclotella meneghiniana were less abundant. Both diatom indices and physicochemical data indicated poor water quality in the Kuils River. The study concludes that diatoms are a valuable tool for biomonitoring river water quality and recommends their use alongside traditional physicochemical methods for future assessments of river sys-tems.

Biogeochemistry of waters is an essential regulator of phytoplankton dynamics, determining the level of species bloom and the change of dominants. The paper investigated the seasonal dynamics of phytoplankton and the nutrient concentration and their ratios in the NE Black Sea in 2017-2021. Two taxonomic groups, diatoms, and coccolithophores, determine seasonal dynamics and significantly contribute to the total phytoplankton biomass. Coccolithophores annually, except in 2020, formed bloom in early June. Large diatoms in summer annually, except in 2019, dominated with biomass exceeding 1000 mg m-3. During the bloom of these taxonomic groups, their contribution to the total phytoplankton biomass exceeded 90%. Each group has characteristic biogeochemical niches in the nitrogen and phosphorus concentrations coordinates. The regulation of the biogeochemistry of water is the position of the seasonal thermocline. With a high-lying and sharp gradient thermocline (the average for five years is 6.87 m), low nitrogen concentrations and a nitrogen-to-phosphorus ratio below the Redfield ratio are created in the upper mixed layer. These conditions are optimal for the dominance of coccolithophores. When the thermocline is deepened (the average for five years is 17.96 m), the phosphorus concentration decreases significantly and the ratio of nitrogen to phosphorus is significantly higher than the Redfield ratio, and these conditions lead to the dominance of large diatoms. The results of experimental studies with nitrogen and phosphorus additives in the natural phytoplankton population confirm the above statements. The addition of phosphorus leads to an increased role of coccolithophores in the total phytoplankton biomass, the addition of nitrogen alone contributes to the growth of large diatoms, and the combined addition of phosphorus and nitrogen in a ratio close to the Redfield ratio leads to the dominance of small diatoms.

The pennate diatom Phaeodactylum tricornutum is a model organism able to synthesize industrially-relevant molecules. Commercial-scale cultivation currently requires large monocultures, prone to bio-contamination. However, little is known about the identity of the invading organisms. To reduce the complexity of natural systems, we systematically investigated the microbiome of non-axenic P. tricornutum cultures from a culture collection in reproducible experiments. The results revealed a dynamic bacterial community that developed differently in “complete” and “minimal” media conditions. In complete media, we observed an accelerated “culture crash”, indicating a more stable culture in minimal media. The identification of only four bacterial families as major players within the microbiome suggests specific roles depending on environmental conditions. From our results we propose a network of putative interactions between P. tricornutum and these main bacterial factions. We demonstrate that, even with rather sparse data, a mathematical model can be reconstructed that qualitatively reproduces the observed population dynamics, thus indicating that our hypotheses regarding the molecular interactions are in agreement with experimental data. Whereas the model in its current state is only qualitative, we argue that it serves as a starting point to develop quantitative and predictive mathematical models, which may guide experimental efforts to synthetically construct and monitor stable communities required for robust upscaling strategies.

Microalgae are a source of carotenoids, phycocyanin, phenol, amino acids, polyunsaturated fatty acids, sulfated polysaccharides, pigments, and other bioactive molecules with antimicrobial, antioxidant, antiviral, antitumor, anti-inflammatory, and fat-burning properties. The increasing incidence of infectious processes, including tuberculosis, caused by antimicrobial resistant strains of microorganisms necessitates the search for alternative sources of compounds with antimicrobial activity, including microalgae. In this study, the antimicrobial properties of marine and freshwater microalgae extracts were evaluated against Gram-positive (Staphylococcus aureus, Enterococcus faecalis, and Streptococcus pyogenes) and Gram-negative (Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa), Mycobacterium tuberculosis strain H37Rv and Mycobacterium smegmatis. Water, dimethyl sulfoxide, and ethanol were used as extractants. The obtained microalgae extract exhibited cytotoxicity against splenocytes and, to a lesser extent, against peritoneal macrophages of CBA mice. The bacteriostatic effect of the microalgae extracts against bacteria and mycobacteria was demonstrated by MTT test. In addition, activation of bacterial and mycobacterial growth was observed in a number of cases with high levels of microalgae extracts in the medium. In an expression model of tuberculosis in mice, a decrease in mycobacterial load in the lungs and spleen was observed. Thus, microalgae have moderate to weak antimicrobial activity.

There is little information about moisture changes in different altitudinal belts in mountainous regions of the Southern Russian Far East. We present ecological-taxonomic composition of the diatom flora, the botanical composition of peat of small mountain lake/mire complexes located in the Central Sikhote-Alin within large landslides on the paleovolcano slopes are identified. Frequent changes in diatom assemblages and peat-forming plants indicate unstable hydroclimatic conditions with varying degrees of watering and dry condition up to complete overgrowth of the lakes. Frequent change of sphagnum mosses with different trophic preferences was established. The chronology is based on 11 radiocarbon dates. Accumulation rates reached up to 1.9 mm/year, the temporal resolution for the reconstructions is up to 30–40 years. The tendencies of lake evolution depended on different-scale hydroclimatic changes for the last 4400 yr. The most detailed data for the last 2600 yr were obtained from the Nizhnee Lake sequence, more sensitive to climatic changes. The main reason for the change in the hydrological regime of the lakes was variations in precipitation during short-term climatic changes. The sediment record moisture fluctuations are relatively well correlated with regional patterns reflecting summer monsoon intensity and cyclogenesis activity.

For the water bodies of the Lena Delta Nature Reserve, 413 taxa were known. In 14 small tundra reservoirs in its vicinity, we identified 385 taxa, which in the compilatory list made up a significant diversity (666 taxa including definitions to the genus level) of diatoms. Thus, the species composition of diatoms in the reserve and adjacent territories was replenished by 278 species. The predominance of species of the genera Pinnularia (57) and Eunotia (51) at the family and generic levels was revealed. Index of intraspecific variability Ssp./Sp. for the lakes of the reserve was 1.11, and for the lakes of the Tiksi region 1.14, which is typical for high-latitude and high-mountain communities. The number of rare or endangered species varied in different lakes within 1-10, totaling 42 species for the entire study area. Bioindication has shown that potentially threatened species prefer moderate temperatures, slightly acidic or neutral environments free from organic pollution. A comparative analysis of the species composition of diatoms in the vicinity of the Lena Delta and other northern water bodies of Yakutia and the Arctic Islands showed that the species composition of each lake in the Arctic is strictly individual. The indicator characteristics show a certain response of the species composition of diatoms to changes in salinity, pH, and organic pollution. A number of regularities in the spatial distribution of diatoms in the study area were found in connection with the physicochemical parameters of their habitat, height above sea level, and relation to a particular catchment basin. Statistical mapping of indicators of community and habitat diversity revealed a strong reaction to point one-time pollution and made it possible to assume the influence of summer northeast winds on the species composition. We suggest that the high diversity inherent in the diatom lakes of the Tiksi coastal zone, which can even be replenished in further studies, can be considered as a property of coastal biota inherent in ecotones. Since it is in the coastal Tiksi region that a surge in the number of species is observed, this region can be considered not only an ecotone, but also a hotspot of diatom diversity. The results of the study are important for developing the basis for monitoring biodiversity under the conditions of anthropogenic and climatic changes in the Arctic.

Diatoms are single-celled photosynthetic eukaryotes responsible for CO2 fixation and primary production in aquatic ecosystems. The cosmopolitan marine diatom Coscinodiscus granii can form seasonal blooms in coastal areas and interact with various microorganisms, including the parasitic oomycete Lagenisma coscinodisci. This unicellular eukaryote is mainly present in the northern hemisphere as an obligate parasite of the genus Coscinodiscus. Understanding the interplay of abiotic factors such as temperature and biotic factors like parasitism on algal physiology is crucial as it dictates plankton community composition and is especially relevant in climate change. This study investigates the impact of two temperatures, 13°C and 25°C, on Coscinodiscus granii under laboratory conditions. A decreased infection rate of the parasite was observed at the elevated temperature. Comparative metabolomic analysis using UHPLC-HRMS revealed that temperature and parasitism significantly affect the algal metabolome. Abundances of metabolites related to sulfur metabolism, including cysteinoleic acid and dimethylsulfoniopropionate, as well as molecules linked to fatty acid metabolism, e.g., carnitine, acetylcarnitine, and eicosapentaenoic acid, significantly increase in cells grown at a higher temperature, suggesting the enhanced rate of metabolism of host cells as temperature rises. Our study reveals how temperature-induced metabolic changes can influence host-parasite dynamics in a changing climate.

The altitude of the habitat is one of the important regulators of species survival. Kaçkar Mountains National Park is located in the Eastern Black Sea region of Turkey. This is the first study on the benthic diatom flora of the high mountain lakes in Kaçkar Mountains National Park, which is situated between 2782 and 3075 m a.s.l. A total of 84 diatom species were identified from benthic communities of 15 habitats in summer (19 July, 28 August) and autumn (10 September) months of 2020. The genus Pinnularia (13 species) formed the basis of the taxonomic list followed by Eunotia (5 species), Navicula (5 species), and Frustulia (4 species) genera, respectively. The waters in all the studied lakes were fresh, low-saline, with low-alkaline or circumneutral pH and organically uncontaminated as evidenced by prevailed bioindicator groups. Statistical methods and comparative floristic results confirm the role of the lake altitude for the diatom species distribution. Species richness was higher in lakes with lower altitude, but a statistical approach also revealed a tendency for it to increase with altitude if species richness increased. Further studies will be needed to continue exploring this pattern. In the first round of analysis, diatom species groups were categorized according to IUCN categories, revealing one potentially threatened and one rare species. To protect studied high mountain lakes, their ecological conditions must be constantly monitored in the Kaçkar Mountains National Park.