Search Results (58)

Kleptoplastidy is a nutrition mode in which cells of protists and some multicellular organisms acquire, maintain, and exploit chloroplasts of prey algae cells as photosynthesis reactors. It is an important aspect of the mixotrophic feeding strategy, which plays a role in the formation of harmful algae blooms (HABs). We developed a new mathematical model, in which kleptoplastidy is regarded as a mechanism of enhancing mixotrophy of protists. The model is constructed using three thought (theoretical) experiments and the concept of biological time. We propose to measure the contribution of kleptoplastidy to mixotrophy using a new ecological indicator: the kleptoplastidy index. This index is a function of two dimensionless variables, one representing the ratio of photosynthetic production of acquired chloroplasts versus native chloroplasts, and the other representing the balance between autotrophic and heterotrophic feeding modes. The index is tested by data for the globally distributed, bloom-forming potentially toxic mixotrophic dinoflagellates Prorocentrum cordatum. The model supports our hypothesis that kleptoplastidy can increase the division rate of algae significantly (by 40%), thus boosting their population growth and promoting blooms. The proposed model can contribute to advancements in ecological modeling aimed at forecasting and management of HABs that deteriorate marine coastal environments worldwide. Full article

The larger benthic foraminifera is a group of marine protists harbouring symbiotic algae, that are geographically confined to shallow tropical and subtropical waters, often associated with coral reefs. The resulting controls on availability of habitat and rates of dispersion make these foraminifers, particularly the genus Amphistegina, useful proxies in the study of invasive marine biota, transported through hull fouling and ballast water contamination in modern commercial shipping. However, there is limited information on the importance of these dispersal mechanisms for foraminifers in the Pre-Industrial Era (pre-1850) for the Atlantic and Caribbean region. This paper examines possible constraints and vectors controlling the invasion of warm-water taxa from the Indo-Pacific region to the Atlantic and Caribbean region. Heterostegina depressa, first described from St. Helena, a remote island in the South Atlantic, provides a test case. The paper postulates that invasions through natural range expansion or ocean currents were unlikely along the possible available routes and hypothesises that anthropogenic vectors, particularly sailing ships, were the most likely means of transport. It concludes that the invasion of the Atlantic by H. depressa was accomplished within the Little Ice Age (1350–1850 C.E.), during the period between the start of Portuguese marine trade with east Africa in 1497 and the first description of H. depressa in 1826. This hypothesis is likely applicable to other foraminifers and other biota currently resident in the Atlantic and Caribbean region. The model presented provides well-defined parameters that can be tested using methods such as isotopic dating of foraminiferal assemblages in cores and genetic indices of similarity of geographic populations. Full article

The thraustochytrids are a group of marine protists known for their significant ecological roles as decomposers and parasites as well as for their potential biotechnological applications, yet their evolutionary and structural diversity remains poorly understood. Our review critically examines the phylogeny of this taxa, utilizing available up-to-date knowledge and their taxonomic classifications. Additionally, advanced imaging techniques, including electron microscopy, are employed to explore the ultrastructural characteristics of these organisms, revealing key features that contribute to their adaptive capabilities in varying marine environments. The integration of this knowledge with available omics data highlights the huge biotechnological potential of thraustochytrids, particularly in producing $\omega$-3 fatty acids and other bioactive compounds. Our review underscores the importance of a systems biology approach in understanding thraustochytrids biology and highlights the urgent need for novel, accurate omics research to unlock their full biotechnological potential. Overall, this review aims to foster a deeper appreciation of thraustochytrids by synthesizing information on their evolution, ultrastructure, and practical applications, thereby providing a foundation for future studies in microbiology and biotechnology. Full article

Protists inhabit marine, brackish and fresh waters. The salt barrier plays an important role in the origin of their diversity. Salinity tolerance differs among species and sometimes even among different strains of the same species, indicating local adaptation. Dinoflagellates from the Apocalathium genus are represented by at least four species, which originated via rapid and recent radiation. Water salinity was suggested as one of the key factors for this radiation. A previous study found RNA transcripts, which belong exclusively to saline strains of Apocalathium, and were absent in its freshwater strains. In the present paper, the diversity of these transcripts and their orthologs from marine and freshwater protists were analysed using bioinformatic approaches. First, it was found that these specific transcripts translated to the proteins, which are important for osmoregulation (e.g., transport of various compounds including glycine betaine, regulation of microtubule organisation, post transcriptional modifications). This supports the idea that speciation within Apocalathium resulted in the loss of osmoregulatory genes by freshwater species. Second, protein distribution was not highly species specific, because their orthologs were found in different dinoflagellates and were relatively common in other phototrophic protists, though the sequences were highly variable. Proteins from 13 orthogroups were absent or very rare in studied freshwater genomes and transcriptomes. They could play a specific role in protists salinity tolerance. Third, detailed phylogenetic analyses of betaine-like transporter and chloride transmembrane transporters, which probably are one of the key proteins associated with salinity tolerance, revealed high levels of multiple and variable copies that were not eliminated from the genome during the evolution. The expression of their genes could be important in the adaptation of dinoflagellates to salinity changes, as it was already shown for some other protists. Full article

The Canary Islands are considered a hot spot for marine species biodiversity. Each stranded cetacean has provided important scientific, biological and pathological information. The morphological identification of parasites in these stranded cetaceans is the main aim of the present article. An investigation to identify parasites was carried out in 233 stranded animals (2018–2022), which were submitted for necropsy. Adult and sub-adult/juvenile animals were the most parasitized age categories, and eighteen parasite species were morphologically identified, including nematodes (Crassicauda grampicola, Crassicauda anthonyi, Halocercus delphini, Anisakis simplex, Stenurus globicephalae, Stenurus ovatus), trematodes (Nasitrema delphini, Oschmarinella rochebruni, Brachycladium atlanticum, Pholeter gastrophilus), cestodes (Clistobothrium delphini, Clistobothrium grimaldii), acanthocephalans (Bolbosoma vasculosum, Bolbosoma capitatum), protists (Toxoplasma gondii) and crustaceans (Conchoderma auritum, Xenobalanus globicipitis, Pennella balaenoptera), as well as nine genera: Crassicauda sp., Halocercus sp., Anisakis sp., Stenurus sp., Nasitrema sp., Oschmarinella sp., Dyphyllobothrium sp., Cyamus sp., Conchoderma sp., and Sarcocystis sp. These could not be identified at the species level. Differences in the host specificity of some parasites were observed, varying in prevalence. The accurate morphological identification of the parasites affecting these marine mammals is essential to understanding disease epidemiology, assessing cetacean populations’ health status, and developing effective conservation and management strategies. Full article

Plankton studies serve as a basis for marine ecosystem research, but knowledge of marine plankton is still incomplete due to its extreme taxonomic and functional complexity. The application of metabarcoding is very valuable for the characterisation of the plankton community. The plankton community of the Southern Adriatic is subject to strong environmental fluctuations and changes, which underlines the need for frequent, reliable and comprehensive characterisation of the plankton. The aim of this study was to determine the taxonomic composition and seasonal distribution of eukaryotic plankton in the Southern Adriatic. Plankton samples were collected monthly for one year at the coastal station of the Southern Adriatic and metabarcoding was used for taxonomic identification. The results showed a high taxonomic diversity and dynamic seasonal distribution patterns for both the protist and metazoan plankton communities. Metabarcoding revealed both the core, year-round plankton community and previously unrecorded plankton organisms in the Southern Adriatic. The results provide for the first time a comprehensive overview of the plankton community in this area by metabarcoding. The identified seasonal patterns of plankton genera and species in the Southern Adriatic will contribute to the understanding of plankton interactions and future changes in community diversity characterisation. Full article

The world’s oceans and seas host >100 known strains of thraustochytrids, a common group of marine eukaryotic unicellular protists, residing in diverse marine habitats, with many others to be isolated and cultivated. The thraustochytrids have become of considerable industrial interest due to health benefits gained from their high percentages of valuable bioactive compounds, revealing the needs for the isolation of new potential strains. Employing a recently developed isolation methodology (use of cell culture medium), we assess initial culture conditions and growth paces of newly isolated thraustochytrid cells (thraustochytrid sp. BSH), originated from the colonial tunicate Botryllus schlosseri, residing on Helgoland Island, Germany. Cells were cultivated under static versus agitated conditions, along with two inoculation sizes (0.5 × 10⁶ and 1 × 10⁶ cells/dish) and in three vessel types (35 mm Petri dishes and T25 and T75 flasks; containing 3, 5 and 15 mL medium, respectively). Cultures were observed under regular microscopy, confocal microscopy and H&E staining. While cells in all conditions grew fast, results revealed the superiority of agitated cultivation in T75 flasks inoculated with 0.5 × 10⁶ cells/dish (6.41 ± 1.91-fold increase/week). Further, 18S rDNA revealed high similarities (99.5–99.8) of strain BSH to two thraustochytrid strains from Monterey, California (USA), B. schlosseri colonies, elucidating a new understanding of these animals-protists associations. Full article

Heterotrophic protists are key components of marine ecosystems. They act as controllers of bacterial and microphytobenthos production and contribute significantly to the carbon flux to higher trophic levels. Still, metabarcoding studies on benthic protist communities are much less frequent than for planktonic organisms. Especially in the Baltic Sea, representing the largest brackish water environment on earth, so far, no extensive metabarcoding studies have been conducted to assess the diversity of benthic protists in this unique and diverse habitat. This study aims to give first insights into the diversity of benthic protist communities in two different regions of the Baltic Sea, Fehmarnbelt, and Oderbank. Using amplicon sequencing of the 18S rDNA V9 region of over 100 individual sediment samples, we were able to show significant differences in the community composition between the two regions and to give insights into the vertical distribution of protists within the sediment (0–20 cm). The results indicate that the differences in community composition in the different regions might be explained by several abiotic factors such as salinity and water depth, but are also influenced by methodological aspects such as differences between DNA and RNA results. Full article

Protists are key components of the microbial food web in marine pelagic systems because they link algal and bacterial production to higher trophic levels. However, their functioning and bathymetric distribution in benthic deep-sea ecosystems are still only poorly understood. However, biogeographical patterns of communities can be coupled to the functioning of ecosystems and are therefore important to understand ecological and evolutionary processes. In this study, we investigated the diversity and distribution of benthic protist communities from the sublittoral down to the deep seafloor (50–2000 m) around three islands of the Azores in the North Atlantic Ocean. Using amplicon sequencing of the V9 region (18S rDNA) of 21 samples, we found that protist community compositions from different depths were significantly different. Three assemblages were separated along the following depths: 50 m, 150–500 m and 1000–2000 m, which indicate that deep-sea areas surrounding islands might act as isolating barriers for benthic protist species. A limited gene flow between the communities could favor speciation processes, leading to the unique protist communities found at the different investigated islands. Full article

Microbes in marine sediments constitute up to five-sixths of the planet’s total biomass, but their diversity is little explored, especially for those forming associations with unicellular protists. Heterotrophic ciliates are among the most dominant and diversified marine benthic protists and comprise hotspot niches of bacterial colonization. To date, studies using culture-independent single-cell approaches to explore microbiomes of marine benthic ciliates in nature are almost absent, even for the most ubiquitous species. Here, we characterize the major bacterial groups associated with a representative marine benthic ciliate, Geleia sp. YT, collected directly from the coastal zone of Yantai, China. PacBio sequencing of the nearly full-length 16Sr RNA genes was performed on single cells of Geleia. Fluorescence in situ hybridization (FISH) analysis with genus-specific probes was further applied to locate the dominant bacterial groups. We identified a Variovorax-like bacterium as the major epibiotic symbiont residing in the kineties of the ciliate host. We provide evidence of a nucleus-associated bacterium related to the human pathogen Mycoplasma, which appeared prevalently in the local populations of Geleia sp. YT for 4 months. The most abundant bacterial taxa associated with Geleia sp. YT likely represent its core microbiome, hinting at the important roles of the ciliate-bacteria consortium in the marine benthos. Overall, this work has contributed to the knowledge of the diversity of life in the enigmatic marine benthic ciliate and its symbioses. Full article

Pacific oysters (Crassostrea gigas) are widely cultured in Chinese marine ranching with high economic value. However, mass death of farmed oysters has occurred frequently in recent years because of diseases and environmental disturbance (e.g., high temperatures). In order to analyze the potential relationships between microorganisms and the death of farmed oysters, we compared the dynamics of bacterial and protist communities in oysters at different growth phases using high-throughput sequencing. The results showed that the microbial communities in farmed oysters significantly changed and were markedly different from microbes in natural oysters and the surrounding environments. The number of biomarker taxa among farmed oysters and their surrounding environments decreased gradually with the growth of oysters. During the mass death of farmed oysters, the microbial communities’ abundance of ecological function genes changed, and the correlations among microorganisms disappeared. These results enrich our understanding of the dynamics of microbial communities in farmed oysters at different growth phases, illustrating the characteristics of interactions among microorganisms during the mass death of farmed oysters. Our study is beneficial to promote the healthy aquaculture of oysters. Full article

Thraustochytrids are unicellular marine heterotrophic protists, which have recently shown a promising ability to produce omega-3 fatty acids from lignocellulosic hydrolysates and wastewaters. Here we studied the biorefinery potential of the dilute acid-pretreated marine macroalgae (Enteromorpha) in comparison with glucose via fermentation using a previously isolated thraustochytrid strain (Aurantiochytrium limacinum PKU#Mn4). The total reducing sugars in the Enteromorpha hydrolysate accounted for 43.93% of the dry cell weight (DCW). The strain was capable of producing the highest DCW (4.32 ± 0.09 g/L) and total fatty acids (TFA) content (0.65 ± 0.03 g/L) in the medium containing 100 g/L of hydrolysate. The maximum TFA yields of 0.164 ± 0.160 g/g DCW and 0.196 ± 0.010 g/g DCW were achieved at 80 g/L of hydrolysate and 40 g/L of glucose in the fermentation medium, respectively. Compositional analysis of TFA revealed the production of equivalent fractions (% TFA) of saturated and polyunsaturated fatty acids in hydrolysate or glucose medium. Furthermore, the strain yielded a much higher fraction (2.61–3.22%) of eicosapentaenoic acid (C20:5n-3) in the hydrolysate medium than that (0.25–0.49%) in the glucose medium. Overall, our findings suggest that Enteromorpha hydrolysate can be a potential natural substrate in the fermentative production of high-value fatty acids by thraustochytrids. Full article

Endolimax is a genus of intestinal amoebae which stands among the least known human protists. Previous studies on amoebic systemic granulomatosis of a marine fish (Solea senegalensis) resulted in the unexpected characterization of a new organism which was related to Endolimax and named E. piscium. The existence of multiple reports of systemic granulomatosis caused presumptively by unidentified amoebae in goldfish lead us to investigate the organism involved in goldfish disease. Analysed goldfish presented small whitish nodules in the kidney, which correspond to chronic granulomatous inflammatory reactions with a ring-layer of amoebae in the periphery. Amoebae were amitochondriate and were located in a parasitophorous vacuole within macrophages, as previous studies on this condition in goldfish and other freshwater fish pointed out. SSU rDNA characterization confirmed a new Endolimax lineage which appears closely related to E. piscium, but the molecular evidence, distinct pathological features and lack of ecological overlapping between the hosts support their assignment to a new species, E. carassius. The results support the existence of a considerable unexplored diversity of Endolimax spp. among fish, and their proper characterization can contribute to an understanding of Archamoebae evolution and pathogenic potential. Full article

Thraustochytrids are unicellular heterotrophic marine protists that have been described as producing a high content of polyunsaturated fatty acids (PUFAs). Among them, arachidonic acid (ARA) stands out as a precursor of several mediators of pivotal importance for the immune system. However, the biotechnological potential of thraustochytrids for ARA production has not been developed. The objective of this study is to isolate and identify native strains from different Chilean coastal environments and evaluate in vitro the effect of culture parameters such as C/N ratio (19 and 33) and temperature (15 °C and 23 °C) on biomass production and arachidonic acid content. A total of nine strains were identified and classified into four genera of the Thraustochitridae family. The Lng2 strain with 99% identity belongs to the species Ulkenia visurgenis and was the most prominent one for ARA production. Temperature had an effect on the PUFA profile but not on the ARA content nor on the biomass yield. Additionally, the C/N ratio has been identified as a key parameter. The ARA productivity increased by 92% (from 0.6 to 8.3 ARA mg/g-DW) and its total biomass by 62.7% (from 1.9 to 5.1 g/L) at a high C/N ratio (33) as compared to the control. Full article

High-throughput sequencing technologies have revolutionized microbial diversity studies, shedding light on the oceans’ plankton evolution, distribution, and biological activity. Whereas marine prokaryotes have been more extensively studied and specific methods developed, the research on microbial eukaryotes (protists) is falling behind, with major groups still largely unknown regarding their ecology and function. Because of numerous anthropogenic pressures, it is increasingly important to highlight the functional roles of protists in marine ecosystems. This review outlines the practices, challenges, and opportunities of high-throughput sequencing approaches (i.e., metabarcoding, metagenomics, and metatranscriptomics) to disentangle evolutionary, ecological, and functional aspects of protists in the ocean. These multidimensional approaches allow us to move from the classic picture of microbial biogeography towards functional microbial biogeography, explicitly highlighting the role of protists therein. We provide resources for functional classification and reflect on the current and future potential. We outline aspects of detecting and describing ecosystem changes at the species, population, and community levels, advancing methodological approaches for studying taxonomic diversity towards functional and evolutionary biodiversity concepts, seeking a more complete understanding and monitoring of ocean ecosystems. Full article