Refurbishing the marine parasitoid order Pirsoniales with newly (re)described marine and freshwater free-living predators.

Pirsoniales is a stramenopile order composed of marine parasitoids of diatoms with unique life cycle. Until recently, a single genus, Pirsonia, uniting six species, was known. The recent identification of new free-living eukaryotrophic Pirsoniales Pirsonia chemainus, Feodosia pseudopoda, and Koktebelia satura changed our understanding of this group as exclusively parasitic. However, their cell ultrastructure and feeding preferences were not fully studied due to the death of the cultures. In this study, we re-isolated some of these Pirsoniales and established six new strains exhibiting predatory behavior, including a first freshwater representative. This allowed us to describe five new genera and species, as well as to emend the diagnosis of the order Pirsoniales. The 18S rRNA gene phylogenetic analysis revealed the position of new strains within Pirsoniales and their relationships with parasitoid relatives and environmental sequence lineages. Feeding experiments on novel Pirsoniales strains using diverse algal prey showed that they were not able to form trophosomes and auxosomes. The ability of cell aggregation in Pirsoniales was observed for the first time. One of the studied strains contained intracellular gammaproteobacteria distantly related to Coxiella. Ultrastructural analyses revealed a more complex cytoskeleton structure in Pirsoniales than previously thought and supported the monophyly of Bigyromonadea and Pseudofungi.

Morphological and molecular characterization of a new member of the phylum Rhodelphidia.

Rhodelphidia is a recently discovered phylum within the supergroup Archaeplastida, comprising only two known representatives (Rhodelphis marinus and Rhodelphis limneticus). Despite its close phylogenetic relatedness to red algae, Rhodelphidia differ markedly by being nonphotosynthetic eukaryotrophic flagellates with gene- and intron-rich genomes. Here, we describe a new freshwater Rhodelphidia species, Rhodelphis mylnikovi sp. n., strain Rhod-M. It shows clear morphological differences with the two other Rhodelphis species, including larger cell body size, presence of two contractile vacuoles, short and blunt pseudopodia, absence of cysts, and tendency to cannibalism. 18S rRNA-based phylogenetic analysis placed it sister to the freshwater species R. limneticus.

Phylogenomic position of genetically diverse phagotrophic stramenopile flagellates in the sediment-associated MAST-6 lineage and a potentially halotolerant placididean.

Unlike morphologically conspicuous ochrophytes, many flagellates belonging to basally branching stramenopiles are small and often overlooked. As a result, many of these lineages are known only through molecular surveys and identified as MArine STramenopiles (MAST), and remain largely uncharacterized at the cellular or genomic level. These likely phagotrophic flagellates are not only phylogenetically diverse, but also extremely abundant in some environments, making their characterization all the more important. MAST-6 is one example of a phylogenetically distinct group that has been known to be associated with sediments, but little else is known about it. Indeed, until the present study, only a single species from this group, Pseudophyllomitus vesiculosus (Pseudophyllomitidae), has been both formally described and associated with genomic information. Here, we describe four new species including two new genera of sediment-dwelling MAST-6, Vomastramonas tehuelche gen. et sp. nov., Mastreximonas tlaamin gen. et sp. nov., one undescribed Pseudophyllomitus sp., BSC2, and a new species belonging to Placididea, the potentially halotolerant Haloplacidia sinai sp. nov. We also provide two additional bikosian transcriptomes from a public culture collection, to allow for better phylogenetic reconstructions of deep-branching stramenopiles. With the SSU rRNA sequences of the new MAST-6 species, we investigate the phylogenetic diversity of the MAST-6 group and show a high relative abundance of MAST-6 related to M. tlaamin in samples across various depths and geographical locations. Using the new MAST-6 species, we also update the phylogenomic tree of stramenopiles, particularly focusing on the paraphyly of Bigyra.

Microbial predators form a new supergroup of eukaryotes.

Molecular phylogenetics of microbial eukaryotes has reshaped the tree of life by establishing broad taxonomic divisions, termed supergroups, that supersede the traditional kingdoms of animals, fungi and plants, and encompass a much greater breadth of eukaryotic diversity1. The vast majority of newly discovered species fall into a small number of known supergroups. Recently, however, a handful of species with no clear relationship to other supergroups have been described2-4, raising questions about the nature and degree of undiscovered diversity, and exposing the limitations of strictly molecular-based exploration. Here we report ten previously undescribed strains of microbial predators isolated through culture that collectively form a diverse new supergroup of eukaryotes, termed Provora. The Provora supergroup is genetically, morphologically and behaviourally distinct from other eukaryotes, and comprises two divergent clades of predators-Nebulidia and Nibbleridia-that are superficially similar to each other, but differ fundamentally in ultrastructure, behaviour and gene content. These predators are globally distributed in marine and freshwater environments, but are numerically rare and have consequently been overlooked by molecular-diversity surveys. In the age of high-throughput analyses, investigation of eukaryotic diversity through culture remains indispensable for the discovery of rare but ecologically and evolutionarily important eukaryotes.

On the origin of TSAR: morphology, diversity and phylogeny of Telonemia.

Telonemia is a poorly known major phylum of flagellated eukaryotes with a unique combination of morphological traits. Phylogenomics recently revealed the phylogenetic position of telonemids as sister to SAR, one of the largest groups of eukaryotes, comprising Stramenopiles, Alveolata and Rhizaria. Due to this key evolutionary position, investigations of telonemids are of critical importance for elucidating the origin and diversification of an astounding diversity of eukaryotic forms and life strategies. To date, however, only two species have been morphologically characterized from Telonemia, which do not represent this genetically very diverse group. In this study, we established cultures for six new telonemid strains, including the description of five new species and a new genus. We used these cultures to update the phylogeny of Telonemia and provide a detailed morphological and ultrastructural investigation. Our data elucidate the origin of TSAR from flagellates with complex morphology and reconstruction of the ancestral structure of stramenopiles, alveolates and rhizarians, and their main synapomorphic characters. Since telonemids are a common component of aquatic environments, the features of their feeding, behaviour and ecological preferences observed in clonal cultures and the results of global metabarcoding analysis contribute to a deeper understanding of organization of microbial food webs.

Biodiversity of a boreal mire, including its hydrographic network (Shichengskoe mire, north-western Russia).

BACKGROUND: The paper is based on the dataset whose purpose was to deliver, in the form of GBIF-mediated data, diverse materials on the biodiversity of a large mire, Shichengskoe mire (Vologda Region, north-western Russia), including its various mire sites and intra-mire water bodies. The dataset was based on our materials collected for two decades (from 2000 to 2021) in different parts and biotopes of the Shichengskoe mire and complemented by scarce data obtained previously by other researchers. The data contain materials on the diversity of Animalia (2886 occurrences), Bacteria (22), Chromista (256), Fungi (111), Plantae (2463) and Protozoa (131). Within the study period, the most detailed and long-term biodiversity studies were carried out for higher plants and invertebrates. On the other hand, the data on the composition of lichens, protozoa, algae, basidiomycetes, some groups of invertebrates and, to a lesser extent, lichens and vertebrates are far less comprehensive and require further substantial research efforts. The list includes occurrences from both the peatland (mire sites and mire margins different in typology) and the objects of the mire hydrographic network. In a standardised form, this article summarises both already published (mainly in Russian) and unpublished materials. NEW INFORMATION: The paper summarises the results of long-term research on the biodiversity of a boreal mire, including its hydrographic network. A total of 5869 occurrences were included in the dataset published in the Global Biodiversity Information Facility (GBIF, gbif.org) for the first time. According to the GBIF taxonomic backbone, the dataset covers 1358 taxa, including 1250 lower-rank taxa (species, subspecies, varieties, forms) and 108 taxa identified to the genus level. Several species found in the Shichengskoe mire, mainly belonging to Bacteria, Chromista and Protozoa, have never been listed in GBIF for the territory of Russia before. The overwhelming majority of occurrences and identified species came from the territory of Shichengskiy Landscape Reserve. Due to our work, this Reserve is now the most studied regional reserve in the Vologda Region with respect to biodiversity. By the number of revealed species, it is close to two federal protected areas: Darwinskiy State Nature Biospheric Reserve and National Park "Russkiy Sever".

Heterotrophic flagellates and centrohelid heliozoans from marine waters of Curacao, the Netherlands Antilles.

Recent progress in understanding the early evolution of eukaryotes was tied to morphological identification of flagellates and heliozoans from natural samples, isolation of their culture and genomic and ultrastructural investigations. These protists are the smallest and least studied microbial eukaryotes but play an important role in the functioning of microbial food webs. Using light and electron microscopy, we have studied the diversity of heterotrophic flagellates and centrohelid heliozoans from marine waters of Curacao (The Netherlands Antilles), and provide micrographs and morphological descriptions of observed species. Among 86 flagellates and 3 centrohelids encountered in this survey, five heterotrophic flagellates and one сentrohelid heliozoan were not identified even to the genus. Some flagellate protists have a unique morphology, and may represent undescribed lineages of eukaryotes of high taxonomic rank. The vast majority (89%) of identified flagellates is characterized by wide geographical distribution and have been reported previously from all hemispheres and various climatic regions. More than half of the species were previously observed not only from marine, but also from freshwater habitats. The parameters of the species accumulation curve indicate that our species list obtained for the Curacao study sites is far from complete, and each new sample should yield new species.

New Lineage of Microbial Predators Adds Complexity to Reconstructing the Evolutionary Origin of Animals.

The origin of animals is one of the most intensely studied evolutionary events, and our understanding of this transition was greatly advanced by analyses of unicellular relatives of animals, which have shown many "animal-specific" genes actually arose in protistan ancestors long before the emergence of animals [1-3]. These genes have complex distributions, and the protists have diverse lifestyles, so understanding their evolutionary significance requires both a robust phylogeny of animal relatives and a detailed understanding of their biology [4, 5]. But discoveries of new animal-related lineages are rare and historically biased to bacteriovores and parasites. Here, we characterize the morphology and transcriptome content of a new animal-related lineage, predatory flagellate Tunicaraptor unikontum. Tunicaraptor is an extremely small (3-5 µm) and morphologically simple cell superficially resembling some fungal zoospores, but it survives by preying on other eukaryotes, possibly using a dedicated but transient "mouth," which is unique for unicellular opisthokonts. The Tunicaraptor transcriptome encodes a full complement of flagellar genes and the flagella-associated calcium channel, which is only common to predatory animal relatives and missing in microbial parasites and grazers. Tunicaraptor also encodes several major classes of animal cell adhesion molecules, as well as transcription factors and homologs of proteins involved in neurodevelopment that have not been found in other animal-related lineages. Phylogenomics, including Tunicaraptor, challenges the existing framework used to reconstruct the evolution of animal-specific genes and emphasizes that the diversity of animal-related lineages may be better understood only once the smaller, more inconspicuous animal-related lineages are better studied. VIDEO ABSTRACT.