Phylogeny of Novel Naked Filose and Reticulose Cercozoa: Granofilosea cl. n. and Proteomyxidea Revised

A novel free-living endomyxan flagellate Viscidocauda repens gen. Nov., sp. nov

Endomyxa comprises a diverse group of protists, including free-living amoebae and parasites, that infect various hosts. In this study, we report a new free-living amoeboflagellate, Viscidocauda repens gen. Nov., sp. nov., isolated from seawater near Hachijojima Island, Japan. V. repens is a gliding bacterivorous biflagellate and occasionally extends pseudopodia from its posterior end. Molecular phylogenetic analysis based on small subunit ribosomal RNA gene sequences places V. repens as sister lineage to a clade comprising the endomyxan Ascetosporea and Gromiidea. Ultrastructural observations revealed that V. repens has four microtubular roots (R1-R4), but lacks vp2, a unique microtubular band widely distributed among cercozoan flagellates. Based on its morphology, ultrastructure, and phylogenetic position, we propose V. repens as a new genus and species within Endomyxa.

Vampyrella crystallifera sp. nov., an Amoeba That Dissolves Entire Algal Cells at a Remarkable Speed

The vampyrellid amoebae (Order Vampyrellida, Rhizaria) comprise predatory microeukaryotes that inhabit freshwater, marine, and terrestrial habitats. They are known to consume a wide array of prey, which includes microalgae, fungi, and even microscopic animals such as nematodes. Members of the popular genus Vampyrella phagocytize the cell contents of filamentous green algae after localized perforation of the cell wall. This feeding strategy, named protoplast extraction, is the hallmark of Vampyrella species and vampyrellid amoebae in general. Here, we report on a new species from a German spring fen, Vampyrella crystallifera sp. nov., which specifically preys on a unicellular zygnematophyte green alga (Nucleotaenium sp.) isolated from the same microhabitat. In contrast to its closest relatives (V. lateritia and V. pendula), V. crystallifera does not feed by protoplast extraction but engulfs whole algal cells, followed by the dissolution of the entire prey cell wall. Given the recalcitrant, plant-like cell walls of the zygnematophytes, this is a remarkable process that might involve enzymes also used by the closely related protoplast feeders. The discovery of V. crystallifera again showcases the exceptional diversity of predator-prey interactions found in the Vampyrellida and adds to our knowledge of protist diversity in temperate moorlands.

The vampyrellid amoeba Strigomyxa ruptor gen. et sp. nov. and its remarkable strategy to acquire algal cell contents

The vampire amoebae (Vampyrellida, Rhizaria) inhabit freshwater, marine, and terrestrial ecosystems and consume a wide range of eukaryotic prey. This includes diverse microalgae, fungi, and microscopic animals. One of the most captivating aspects of the vampyrellids is their ability to extract the cell contents of other eukaryotes after local dissolution of the prey cell wall, a feeding strategy that occurs in several vampyrellid families, but is best studied in Vampyrella species that attack zygnematophyte green algae. Here, we report two new vampyrellid strains from temperate moorlands in Germany with a yet-undescribed feeding strategy: internal protoplast extraction and cell wall regurgitation. This feeding strategy involves the phagocytosis of whole desmid cells (genus Closterium, Zygnematophyceae), internal cleavage of the algal cell wall, extraction of the cell contents, and subsequent exocytosis of bundled empty cell walls. The large primary food vacuole formed during the process has exceptional functions, as it forms internal feeding pseudopodia, packages algal cell contents into smaller secondary vacuoles, and transforms into a "waste vacuole" with cell wall remnants. The new feeding strategy, which - in the widest sense - is reminiscent of the pellet casting of owls, reveals a stunningly sophisticated behavior of single protist cells. Based on morphological, phylogenetic, and autecological data, both vampyrellid strains are nearly identical and here assigned to a new and quite unique vampyrellid taxon, Strigomyxa ruptor gen. et sp. nov. (Leptophryidae, Vampyrellida).

Protozoan communities serve as a strong indicator of water quality in the Nile River

The relationship between the protozoan communities and environmental variables was studied in the Nile River to evaluate their potential as water quality indicators. Protozoans were sampled monthly at six sampling sites in the Nile's Damietta Branch across a spatial gradient of environmental conditions during a 1-year cycle (February 2016-January 2017). The Protozoa community was comprised of 54 species belonging to six main heterotrophic Protozoa phyla. The abundance (average, 1089 ± 576.18 individuals L-1) and biomass (average, 86.60 ± 106.13 μg L-1) were comparable between sites. Ciliates comprised the majority of protozoan species richness (30 species), abundance (79.72%), and biomass (82.90%). Cluster analysis resulted in the distribution of protozoan species into three groups, with the most dominant species being the omnivorous ciliate Paradileptus elephantinus. Aluminium, fluoride, and turbidity negatively affected abundance and biomass, while dissolved oxygen and potassium positively impacted biomass. Of the dominant species recorded over the study area, the amoebozoa Centropyxis aculeata was associated with runoff variables, while the bacterivorous ciliates Colpidium colpoda, Glaucoma scintillans, and Vorticella convallaria were related to the abundance of heterotrophic bacteria, phytoplankton biomass, and total organic carbon. Total dissolved salts, PO4, NH3, NO2, dissolved oxygen, and total organic carbon were the strongest causative factors for protozoa distribution. The α-Mesosaprobic environment at site VI confirmed a high load of agricultural runoffs compared to other sites. This study demonstrates that protozoans can be a potential bioindicator of water quality status in this subtropical freshwater river system.

Arctic cyanobacterial mat community diversity decreases with latitude across the Canadian Arctic

Cyanobacterial mats are commonly reported as hotspots of microbial diversity across polar environments. These thick, multilayered microbial communities provide a refuge from extreme environmental conditions, with many species able to grow and coexist despite the low allochthonous nutrient inputs. The visibly dominant phototrophic biomass is dependent on internal nutrient recycling by heterotrophic organisms within the mats; however, the specific contribution of heterotrophic protists remains little explored. In this study, mat community diversity was examined along a latitudinal gradient (55-83°N), spanning subarctic taiga, tundra, polar desert, and the High Arctic ice shelves. The prokaryotic and eukaryotic communities were targeted, respectively, by V4 16S ribosomal RNA (rRNA) and V9 18S rRNA gene amplicon high-throughput sequencing. Prokaryotic and eukaryotic richness decreased, in tandem with decreasing temperatures and shorter seasons of light availability, from the subarctic to the High Arctic. Taxonomy-based annotation of the protist community revealed diverse phototrophic, mixotrophic, and heterotrophic genera in all mat communities, with fewer parasitic taxa in High Arctic communities. Co-occurrence network analysis identified greater heterogeneity in eukaryotic than prokaryotic community structure among cyanobacterial mats across the Canadian Arctic. Our findings highlight the sensitivity of microbial eukaryotes to environmental gradients across northern high latitudes.

Comparative genomics of Ascetosporea gives new insight into the evolutionary basis for animal parasitism in Rhizaria

BACKGROUND

Ascetosporea (Endomyxa, Rhizaria) is a group of unicellular parasites infecting aquatic invertebrates. They are increasingly being recognized as widespread and important in marine environments, causing large annual losses in invertebrate aquaculture. Despite their importance, little molecular data of Ascetosporea exist, with only two genome assemblies published to date. Accordingly, the evolutionary origin of these parasites is unclear, including their phylogenetic position and the genomic adaptations that accompanied the transition from a free-living lifestyle to parasitism. Here, we sequenced and assembled three new ascetosporean genomes, as well as the genome of a closely related amphizoic species, to investigate the phylogeny, origin, and genomic adaptations to parasitism in Ascetosporea.

RESULTS

Using a phylogenomic approach, we confirm the monophyly of Ascetosporea and show that Paramyxida group with Mikrocytida, with Haplosporida being sister to both groups. We report that the genomes of these parasites are relatively small (12-36 Mb) and gene-sparse (~ 2300-5200 genes), while containing surprisingly high amounts of non-coding sequence (~ 70-90% of the genomes). Performing gene-tree aware ancestral reconstruction of gene families, we demonstrate extensive gene losses at the origin of parasitism in Ascetosporea, primarily of metabolic functions, and little gene gain except on terminal branches. Finally, we highlight some functional gene classes that have undergone expansions during evolution of the group.

CONCLUSIONS

We present important new genomic information from a lineage of enigmatic but important parasites of invertebrates and illuminate some of the genomic innovations accompanying the evolutionary transition to parasitism in this lineage. Our results and data provide a genetic basis for the development of control measures against these parasites.

Rhabdamoeba marina is a heterotrophic relative of chlorarachnid algae

Rhabdamoeba marina is a unique and poorly reported amoeba with an uncertain phylogenetic position. We successfully cultured R. marina from coastal seawater in Japan and performed a molecular phylogenetic analysis using the small subunit ribosomal RNA (SSU rRNA) gene sequence. Our phylogenetic analysis showed that R. marina branched as a basal lineage of Chlorarachnea, a group of marine photosynthetic algae belonging to the phylum Cercozoa within the supergroup Rhizaria. By comparing the ecological and morphological characteristics of R. marina with those of photosynthetic chlorarachneans and other cercozoans, we gained insight into the evolution and acquisition of plastids in Chlorarachnida.

Pseudovampyrella gen. nov.: A genus of Vampyrella-like protoplast extractors finds its place in the Leptophryidae

Vampyrellid amoebae are predatory protists, which consume a variety of eukaryotic prey and inhabit freshwater, marine and terrestrial ecosystems. Although they have been known for almost 150 years, much of their diversity lacks an in-depth characterization. To date, environmental sequencing data hint at several uncharacterized lineages, to which no phenotype is associated. Furthermore, there are numerous historically described species without any molecular information. This study reports on two new vampyrellid strains from moorlands, which extract the protoplasts of Closterium species (Zygnematophyceae). Our data on morphology, prey range specificity and feeding strategy reveal that the studied vampyrellids are very similar to the historically described Vampyrella closterii. However, phylogenetic analyses demonstrate that the two strains do not belong to the genus Vampyrella and, instead, form a distinct clade in the family Leptophryidae. Hence, we introduce a new genus of algivorous protoplast extractors, Pseudovampyrella gen. nov., with the species P. closterii (= V. closterii) and P. minor. Our findings indicate that the genetic diversity of morphologically described vampyrellid species might be hugely underrated.

Characterization of Rosculus vilicus sp. nov., a rhizarian amoeba interacting with Mycobacterium avium subsp. paratuberculosis

Free-living amoebae are described as potential reservoirs for pathogenic bacteria in the environment. It has been hypothesized that this might be the case for Mycobacterium avium subsp. paratuberculosis, the bacterium responsible for paratuberculosis. In a previous work, we isolated an amoeba from a water sample in the environment of infected cattle and showed that this amoeba was associated with Mycobacterium avium subsp. paratuberculosis. While a partial 18S rRNA gene has allowed us to suggest that this amoeba was Rosculus-like, at that time we were not able to sub-cultivate it. In the present study, we succeeded in cultivating this strain at 20-25°C. This amoeba is among the smallest (5-7 μm) described. The sequencing of the whole genome allowed us to extract the full 18S rRNA gene and propose this strain as a new species of the Rosculus genus, i.e., R. vilicus. Of note, the mitochondrial genome is particularly large (184,954 bp). Finally, we showed that this amoeba was able to phagocyte Mycobacterium avium subsp. paratuberculosis and that the bacterium was still observed within amoebae after at least 3 days. In conclusion, we characterized a new environmental amoeba species at the cellular and genome level that was able to interact with Mycobacterium avium subsp. paratuberculosis. As a result, R. vilicus is a potential candidate as environmental reservoir for Mycobacterium avium subsp. paratuberculosis but further experiments are needed to test this hypothesis.

Diversity of 'simple' multicellular eukaryotes: 45 independent cases and six types of multicellularity

Multicellularity evolved multiple times in the history of life, with most reviewers agreeing that it appeared at least 20 times in eukaryotes. However, a specific list of multicellular eukaryotes with clear criteria for inclusion has not yet been published. Herein, an updated critical review of eukaryotic multicellularity is presented, based on current understanding of eukaryotic phylogeny and new discoveries in microbiology, phycology and mycology. As a result, 45 independent multicellular lineages are identified that fall into six distinct types. Functional criteria, as distinct from a purely topological definition of a cell, are introduced to bring uniformity and clarity to the existing definitions of terms such as colony, multicellularity, thallus or plasmodium. The category of clonal multicellularity is expanded to include: (i) septated multinucleated thalli found in Pseudofungi and early-branching Fungi such as Chytridiomycota and Blastocladiomycota; and (ii) multicellular reproductive structures formed by plasmotomy in intracellular parasites such as Phytomyxea. Furthermore, (iii) endogeneous budding, as found in Paramyxida, is described as a form of multicellularity. The best-known case of clonal multicellularity, i.e. (iv) non-separation of cells after cell division, as known from Metazoa and Ochrophyta, is also discussed. The category of aggregative multicellularity is expanded to include not only (v) pseudoplasmodial forms, such a sorocarp-forming Acrasida, but also (vi) meroplasmodial organisms, such as members of Variosea or Filoreta. A common set of topological, geometric, genetic and life-cycle criteria are presented that form a coherent, philosophically sound framework for discussing multicellularity. A possibility of a seventh type of multicellularity is discussed, that of multi-species superorganisms formed by protists with obligatory bacterial symbionts, such as some members of Oxymonada or Parabasalia. Its inclusion is dependent on the philosophical stance taken towards the concepts of individuality and organism in biology. Taxa that merit special attention are identified, such as colonial Centrohelea, and a new speculative form of multicellularity, possibly present in some reticulopodial amoebae, is briefly described. Because of insufficient phylogenetic and morphological data, not all lineages could be unequivocally identified, and the true total number of all multicellular eukaryotic lineages is therefore higher, likely close to a hundred.

Control of Blumeria graminis f. sp. hordei on Barley Leaves by Treatment with Fungi-Consuming Protist Isolates

The obligate biotrophic fungal pathogen Blumeria graminis causes the powdery mildew disease of cereals, which results in large crop losses. Control of B. graminis in barley is mainly achieved by fungicide treatment and by breeding resistant varieties. Vampyrellid amoebae, just like mycophagous protists, are able to consume a variety of fungi. To reveal the impact of some selected fungus-consuming protists on Blumeria graminis f. sp. hordei (Bgh), and to evaluate the possibility of using these protists as biological agents in the future, their feeding behaviour on B. graminis spores on barley leaves was investigated. An experiment was carried out with five different protist isolates (Leptophrys vorax, Platyreta germanica, Theratromyxa weberi U 11, Theratromyxa weberi G7.2 and Acanthamoeba castellanii) and four matched controls, including the food sources of the cultures and the medium. Ten-day-old leaves of barley (Hordeum vulgare cv. Golden Promise) were first inoculated with Blumeria graminis (f. sp. hordei race A6) spores, then treated with protists and fungal colonies on the leaf surfaces were counted under the microscope after 5 days. The isolates L. vorax, P. germanica, and T. weberi U11 did not show a significant reduction in the number of powdery mildew colonies whereas the isolates T. weberi G7.2 and A. castellanii significantly reduced the number of powdery mildew colonies on the leaf surfaces compared to their respective controls. This indicates that these two isolates are capable of reducing B. graminis colonies on barley leaves and are suitable candidates for further investigation for possible use as biological agents. Nevertheless, the susceptibility to dryness and the cell division rate should be considered during the optimisation of the next steps like application procedure and whole plant treatment.

Kinopus chlorellivorus gen. nov., sp. nov. (Vampyrellida, Rhizaria), a New Algivorous Protist Predator Isolated from Large-Scale Outdoor Cultures of Chlorella sorokiniana

The vampyrellids (Vampyrellida, Rhizaria) are a major group of predatory amoebae that have attracted significant attention because of their diversity of feeding strategies. The crucial roles they play in important processes such as suppressing soil disease and controlling aquatic algae, and as microbial contaminants in outdoor large-scale algal cultures, have also received increasing attention.

Molecular data reallocates Sorosphaerula radicalis (Plasmodiophorida, Phytomyxea, Rhizaria) to the genus Hillenburgia

This study reports the first record of Sorosphaerula radicalis (Phytomyxea, Rhizaria) in continental Europe (Tirol, Austria) and provides first molecular data for this species. An 18S rRNA phylogeny placed S. radicalis into the Plasmodiophorida, although distant from other members of the genus Sorosphaerula and close to the parasite of water cress Hillenburgia nasturtii. To resolve this polyphyly, we compare morphological data and life cycles of Sorosphaerula veronicae (the type species of the genus Sorosphaerula), Hillenburgia nasturtii, and Sorosphaerula radicalis. We conclude that Sorosphaerula radicalis belongs to the recently established genus Hillenburgia.

Discovery of the parasite Marteilia cocosarum sp. nov. In common cockle (Cerastoderma edule) fisheries in Wales, UK and its comparison with Marteilia cochillia

Diseases of bivalve molluscs caused by paramyxid parasites of the genus Marteilia have been linked to mass mortalities and the collapse of commercially important shellfish populations. Until recently, no Marteilia spp. have been detected in common cockle (Cerastoderma edule) populations in the British Isles. Molecular screening of cockles from ten sites on the Welsh coast indicates that a Marteilia parasite is widespread in Welsh C. edule populations, including major fisheries. Phylogenetic analysis of ribosomal DNA (rDNA) gene sequences from this parasite indicates that it is a closely related but different species to Marteilia cochillia, a parasite linked to mass mortality of C. edule fisheries in Spain, and that both are related to Marteilia octospora, for which we provide new rDNA sequence data. Preliminary light and transmission electron microscope (TEM) observations support this conclusion, indicating that the parasite from Wales is located primarily within areas of inflammation in the gills and the connective tissue of the digestive gland, whereas M. cochillia is found mainly within the epithelium of the digestive gland. The impact of infection by the new species, here described as Marteilia cocosarum n. sp., upon Welsh fisheries is currently unknown.

Various brain-eating amoebae: the protozoa, the pathogenesis, and the disease

Among various genera of free-living amoebae prevalent in nature, some members are identified as causative agents of human encephalitis, in which Naegleria fowleri followed by Acanthamoeba spp. and Balamuthia mandrillaris have been successively discovered. As the three dominant genera responsible for infections, Acanthamoeba and Balamuthia work as opportunistic pathogens of granulomatous amoebic encephalitis in immunocompetent and immunocompromised individuals, whereas Naegleria induces primary amoebic meningoencephalitis mostly in healthy children and young adults as a more violent and deadly disease. Due to the lack of typical symptoms and laboratory findings, all these amoebic encephalitic diseases are difficult to diagnose. Considering that subsequent therapies are also affected, all these brain infections cause significant mortality worldwide, with more than 90% of the cases being fatal. Along with global warming and population explosion, expanding areas of human and amoebae activity in some regions lead to increased contact, resulting in more serious infections and drawing increased public attention. In this review, we summarize the present information of these pathogenic free-living amoebae, including their phylogeny, classification, biology, and ecology. The mechanisms of pathogenesis, immunology, pathophysiology, clinical manifestations, epidemiology, diagnosis, and therapies are also discussed.

Description of the marine predator Sericomyxa perlucida gen. et sp. nov., a cultivated representative of the deepest branching lineage of vampyrellid amoebae (Vampyrellida, Rhizaria)

The vampyrellids (Vampyrellida, Rhizaria) are naked amoebae of considerable genetic diversity. Three families have been well-defined (Vampyrellidae, Leptophryidae, and Placopodidae), but most vampyrellid lineages detected by environmental sequencing are poorly known or completely uncharacterized. In the brackish sediment of Lake Bras D'Or, Nova Scotia, Canada, we discovered an amoeba with a vampyrellid-like life history that was morphologically dissimilar from previously known vampyrellid taxa. We established a culture of this amoeba, studied its feeding behavior and prey range specificity, and characterized it with molecular phylogenetic methods and light and electron microscopy. The amoeba was a generalist predator (i.e. eukaryotroph), devouring a range of marine microalgae, with a strong affinity for some benthic diatoms and Chroomonas. Interestingly, the amoeba varied its feeding strategy depending on the prey species. Small diatoms were engulfed whole, while larger species were fed on through extraction with an invading pseudopodium. The SSU rRNA gene phylogenies robustly placed the amoeba in the most basal, poorly described lineage ("clade C") of the Vampyrellida. Based on the phylogenetic position and the distinct morphology of the studied amoeba, we here describe it as Sericomyxa perlucida gen. et sp. nov., and establish the new vampyrellid family Sericomyxidae for "clade C."

Parasites, pathogens, and other symbionts of copepods

There is a large diversity of eukaryotic symbionts of copepods, dominated by epizootic protists such as ciliates, and metazoan parasites. Eukaryotic endoparasites, copepod-associated bacteria, and viruses are less well known, partly due to technical limitations. However, new molecular techniques, combined with a range of other approaches, provide a complementary toolkit for understanding the complete symbiome of copepods and how the symbiome relates to their ecological roles, relationships with other biota, and responses to environmental change. In this review we provide the most complete overview of the copepod symbiome to date, including microeukaryotes, metazoan parasites, bacteria, and viruses, and provide extensive literature databases to inform future studies.

Free living amoebae isolation in irrigation waters and soils of an insular arid agroecosystem

The use of freshwater in agricultural systems represents a high percentage of total water consumption worldwide. Therefore, alternative sources of water for irrigation will need to be developed, particularly in arid and semi-arid areas, in order to meet the growing demand for food in the future. The use of recycled wastewater (RWW), brackish water (BW) or desalinated brackish water (DBW) are among the different non-conventional water resources proposed. However, it is necessary to evaluate the health risks for humans and animals associated with the microbiological load of these waters. Protozoa such as free-living amoebae (FLA) are considered an emerging group of opportunistic pathogens capable to cause several diseases in humans (e.g. cutaneous and ocular infections, lung, bone or adrenal gland conditions or fatal encephalitis). In the present study we evaluate FLA presence in three different irrigation water qualities (RWW, BW and DBW) and its survival in irrigated agricultural soils of an extremely arid insular ecosystem (Fuerteventura, Canary Islands, Spain). Samples were cultured on 2% Non-Nutrient Agar (NNA) plates covered with a thin layer of heat killed E. coli and checked daily for the presence of FLA. According to the prevalence of FLA, Vermamoeba vermiformis (53,8%), Acanthamoeba spp. (30,8%), Vahlkampfia avara (7,7%) and Naegleria australiensis (7,7%) were detected in the analysed water samples, while Acanthamoeba (83,3%), Cercozoa spp. (8,3%) and Vahlkampfia orchilla (8,3%) were isolated in irrigated soils. Only Acanthamoeba strains were isolated in no irrigated soils used as control, evidencing the capability of these protozoa to resist environmental harsh conditions. Additionally, all analysed water sources and the irrigated soils presented growth of several pathogenic bacteria. Therefore, the coexistence in water and soils of pathogenic bacteria and FLA, can mean an increased risk of infection in agroecosystems.

Revised Taxonomy and Expanded Biodiversity of the Phytomyxea (Rhizaria, Endomyxa)

Phytomyxea (phytomyxids) is a group of obligate biotrophic pathogens belonging to the Rhizaria. Some phytomyxids are well studied and include known plant pathogens such as Plasmodiophora brassicae, the causal agent of clubroot disease. Despite this economic importance, the taxonomy and biodiversity of this group are largely cryptic, with many species described in the premolecular area. Some of these species were key for establishing the morphotaxonomic concepts that define most genera to this day, but systematic efforts to include and integrate those species into molecular studies are still lacking. The aim of this study was to expand our understanding of phytomyxid biodiversity in terrestrial environments. Thirty-eight environmental samples from habitats in which novel and known diversity of Phytomyxea was expected were analysed. We were able to generate 18S rRNA sequences from Ligniera verrucosa, a species which is well defined based on ultrastructure. Phylogenetic analyses of the collected sequences rendered the genera Lignera, Plasmodiophora and Spongospora polyphyletic, and identified two novel and apparently diverse lineages (clade 17, clade 18). Based on these findings and on data from previous studies, we formally establish the new genera Pseudoligniera n. gen. for L. verrucosa,Hillenburgia n. gen. for Spongospora nasturtii and revert Plasmodiophora diplantherae to its original name Ostenfeldiella diplantherae.

Haplosporosomes, sporoplasmosomes and their putative taxonomic relationships in rhizarians and myxozoans

This paper reviews current knowledge of the structure, genesis, cytochemistry and putative functions of the haplosporosomes of haplosporidians (Urosporidium, Haplosporidium, Bonamia, Minchinia) and paramyxids (Paramyxa, Paramyxoides, Marteilia, Marteilioides, Paramarteilia), and the sporoplasmosomes of myxozoans (Myxozoa - Malacosporea, Myxosporea). In all 3 groups, these bodies occur in plasmodial trophic stages, disappear at the onset of sporogony, and reappear in the spore. Some haplosporidian haplosporosomes lack the internal membrane regarded as characteristic of these bodies and that phylum. Haplosporidian haplosporogenesis is through the Golgi (spherulosome in the spore), either to form haplosporosomes at the trans-Golgi network, or for the Golgi to produce formative bodies from which membranous vesicles bud, thus acquiring the external membrane. The former method also forms sporoplasmosomes in malacosporeans, while the latter is the common method of haplosporogenesis in paramyxids. Sporoplasmogenesis in myxosporeans is largely unknown. The haplosporosomes of Haplosporidium nelsoni and sporoplasmosomes of malacosporeans are similar in arraying themselves beneath the plasmodial plasma membrane with their internal membranes pointing to the exterior, possibly to secrete their contents to lyse host cells or repel haemocytes. It is concluded that these bodies are probably multifunctional within and between groups, their internal membranes separating different functional compartments, and their origin may be from common ancestors in the Neoproterozoic.

Organic amendment strengthens interkingdom associations in the soil and rhizosphere of barley (Hordeum vulgare)

Anthropogenic modification of soil systems has diverse impacts on food web interactions and ecosystem functioning. To understand the positive, neutral or adverse effects of agricultural practices on the associations of community members of soil microbes and microfaunal biomes, we characterized the effects of different fertilization types (organic, inorganic and a combination of organic and inorganic) on the food web active communities in the bulk soil and rhizosphere compartments in field conditions. We examined the influence of fertilization on (i) individual groups (bacteria, protozoa and fungi as microbe representatives and metazoans as microfauna representatives) and (ii) inter-kingdom interactions (focusing on the interactions between bacteria and eukaryotic groups) both neglecting and considering environmental factors in our analysis in combination with the microbial compositional data. Our results revealed different patterns of biota communities under organic versus inorganic fertilization, which shaped food web associations in both the bulk and rhizosphere compartments. Overall, organic fertilization increased the complexity of microbial-microfaunal ecological associations with inter- and intra- connections among categories of primary decomposers (bacteria and fungi) and predators (protozoa and microfauna) and differences in potential function in the soil food web in both the bulk and rhizosphere compartments. Furthermore, the inter-connections between primary decomposers and predators in bulk soil were more pronounced when environmental factors were considered. We suggest that organic fertilization selects bacterial orders with different potential ecological functions and interactions as survival, predation and cooperation due to more complex environment than those of inorganic or combined fertilization. Our findings support the importance of a comprehensive understanding of trophic food web patterns for soil management systems.

Free-living amoebae and squatters in the wild: ecological and molecular features

Free-living amoebae are protists frequently found in water and soils. They feed on other microorganisms, mainly bacteria, and digest them through phagocytosis. It is accepted that these amoebae play an important role in the microbial ecology of these environments. There is a renewed interest for the free-living amoebae since the discovery of pathogenic bacteria that can resist phagocytosis and of giant viruses, underlying that amoebae might play a role in the evolution of other microorganisms, including several human pathogens. Recent advances, using molecular methods, allow to bring together new information about free-living amoebae. This review aims to provide a comprehensive overview of the newly gathered insights into (1) the free-living amoeba diversity, assessed with molecular tools, (2) the gene functions described to decipher the biology of the amoebae and (3) their interactions with other microorganisms in the environment.

Detection and characterisation of haplosporidian parasites of the blue mussel Mytilus edulis, including description of the novel parasite Minchinia mytili n. sp

The edible mussel Mytilus edulis is a major aquaculture commodity in Europe, with 168000 t produced in 2015. A number of abundant, well characterised parasites of the species are known, though none are considered to cause significant mortality. Haplosporida (Rhizaria, Endomyxa) is an order of protistan parasites of aquatic invertebrates, the best studied of which are the oyster pathogens Haplosporidium nelsoni and Bonamia ostreae. While these species are well characterised within their hosts, the diversity, life-cycle and modes of transmission of haplosporidians are very poorly understood. Haplosporidian parasites have previously been reported from Mytilus spp., however the majority of these remain uncharacterised, and no molecular data exist for any species. In this study, we identified 2 novel haplosporidian parasites of M. edulis present in the UK. The first of these, observed by light microscopy and in situ hybridisation infecting the gills, mantle, gonadal tubules and digestive connective tissues of mussels in the Tamar estuary, England, we describe as Minchinia mytili on the basis of 18S sequence data. The second, observed infecting a single archive specimen collected in Loch Spelve, Mull, Scotland, infects the foot muscle, gills and connective tissue of the digestive gland. Sequence data places this parasite in an uncharacterised clade of sequences amplified from tropical bivalve guts and water samples, sister to H. nelsoni. Screening of water and sediment samples collected at the sample site in the Tamar estuary revealed the presence of both sequence types in the water column, suggesting host-free or planktonic life stages.

Two New Marine Species of Placopus (Vampyrellida, Rhizaria) That Perforate the Theca of Tetraselmis (Chlorodendrales, Viridiplantae)

Vampyrellids (Vampyrellida, Rhizaria) are a major group of predatory amoebae known primarily from freshwater and soil. Environmental sequence data indicate that there is also a considerable diversity of vampyrellids inhabiting marine ecosystems, but their phenotypic traits and ecology remain largely unexplored. We discovered algivorous vampyrellids of the filoflabellate morphotype in coastal habitats in Atlantic Canada, established cultures by single-cell isolation, and characterised three strains using light microscopy, SSU rRNA gene sequencing, feeding experiments and growth experiments at various salinities. These strains exhibit orange, discoid trophozoites with ventral filopodia, moving granules ("membranosomes"), and rolling locomotion, similar to freshwater species previously assigned to Hyalodiscus Hertwig & Lesser, but here moved to Placopus Schulze (due to homonymy with Hyalodiscus Ehrenberg). SSU rRNA gene phylogenies place our strains in two distinct positions within "lineage B3" (here referred to as Placopodidae). Based on these morphological, habitat and molecular data, we describe two new species, Placopus melkoniani sp. nov. and Placopus pusillus sp. nov., both of which feed on chlorophyte flagellates (Tetraselmis, Pyramimonas) and the cryptophyte Chroomonas. They perforate the theca of Tetraselmis to extract the protoplast, and thereby represent the first vampyrellids known to degrade the biochemically exotic cell wall of the Chlorodendrales (Chlorophyta, Viridiplantae).

Multigene phylogeny and cell evolution of chromist infrakingdom Rhizaria: contrasting cell organisation of sister phyla Cercozoa and Retaria

Infrakingdom Rhizaria is one of four major subgroups with distinct cell body plans that comprise eukaryotic kingdom Chromista. Unlike other chromists, Rhizaria are mostly heterotrophic flagellates, amoebae or amoeboflagellates, commonly with reticulose (net-like) or filose (thread-like) feeding pseudopodia; uniquely for eukaryotes, cilia have proximal ciliary transition-zone hub-lattices. They comprise predominantly flagellate phylum Cercozoa and reticulopodial phylum Retaria, whose exact phylogenetic relationship has been uncertain. Given even less clear relationships amongst cercozoan classes, we sequenced partial transcriptomes of seven Cercozoa representing five classes and endomyxan retarian Filoreta marina to establish 187-gene multiprotein phylogenies. Ectoreta (retarian infraphyla Foraminifera, Radiozoa) branch within classical Cercozoa as sister to reticulose Endomyxa. This supports recent transfer of subphylum Endomyxa from Cercozoa to Retaria alongside subphylum Ectoreta which embraces classical retarians where capsules or tests subdivide cells into organelle-containing endoplasm and anastomosing pseudopodial net-like ectoplasm. Cercozoa are more homogeneously filose, often with filose pseudopodia and/or posterior ciliary gliding motility: zooflagellate Helkesimastix and amoeboid Guttulinopsis form a strongly supported clade, order Helkesida. Cercomonads are polyphyletic (Cercomonadida sister to glissomonads; Paracercomonadida deeper). Thecofilosea are a clade, whereas Imbricatea may not be; Sarcomonadea may be paraphyletic. Helkesea and Metromonadea are successively deeper outgroups within cercozoan subphylum Monadofilosa; subphylum Reticulofilosa (paraphyletic on site-heterogeneous trees) branches earliest, Granofilosea before Chlorarachnea. Our multiprotein trees confirm that Rhizaria are sisters of infrakingdom Halvaria (Alveolata, Heterokonta) within chromist subkingdom Harosa (= SAR); they further support holophyly of chromist subkingdom Hacrobia, and are consistent with holophyly of Chromista as sister of kingdom Plantae. Site-heterogeneous rDNA trees group Kraken with environmental DNA clade 'eSarcomonad', not Paracercomonadida. Ectoretan fossil dates evidence ultrarapid episodic stem sequence evolution. We discuss early rhizarian cell evolution and multigene tree coevolutionary patterns, gene-paralogue evidence for chromist monophyly, and integrate this with fossil evidence for the age of Rhizaria and eukaryote cells, and revise rhizarian classification.

Rhizarian 'Novel Clade 10' Revealed as Abundant and Diverse Planktonic and Terrestrial Flagellates, including Aquavolon n. gen

Rhizarian ‘Novel Clade 10’ (NC10) is frequently detected by 18S rRNA gene sequencing studies in freshwater planktonic samples. We describe a new genus and two species of eukaryovorous biflagellate protists, Aquavolon hoantrani n. gen. n. sp. and A. dientrani n. gen. n. sp., which represent the first morphologically characterized members of NC10, here named Aquavolonida ord. nov. The slightly metabolic cells possess naked heterodynamic flagella, whose kinetosomes lie at a right angle to each other and are connected by at least one fibril. Unlike their closest known relative Tremula longifila, they rotate around their longitudinal axis when swimming and only very rarely glide on surfaces. Screening of a wide range of environmental DNA extractions with lineage‐specific PCR primers reveals that Aquavolonida consists of a large radiation of protists, which are most diversified in freshwater planktonic habitats and as yet undetected in marine environments. Earlier‐branching lineages in Aquavolonida include less frequently detected organisms from soils and freshwater sediments. The 18S rRNA gene phylogeny suggests that Aquavolonida forms a common evolutionary lineage with tremulids and uncharacterized ‘Novel Clade 12’, which likely represents one of the deepest lineages in the Rhizaria, separate from Cercozoa (Filosa), Endomyxa, and Retaria.

Phytocercomonas venanatans, a New Species of Cercozoa Associated with Chlorotic Streak of Sugarcane

Chlorotic streak is a global disease of commercial sugarcane (Saccharum spp. hybrids). The disease is transmitted by wet soil, water, as well as in diseased planting material. Although first recognized almost 90 years ago and despite significant research effort, the identity of the causal agent has been elusive. Metagenomic high throughput sequencing (HTS) facilitated the discovery of novel protistan ribosomal and nuclear genes in chlorotic streak-infected sugarcane. These sequences suggest a possible causal agent belonging to the order Cercomonadida (Rhizaria, phylum Cercozoa). An organism with morphological features similar to cercomonads (=Cercomonadida) was isolated into pure axenic culture from internal stalk tissues of infected sugarcane. The isolated organism contained DNA sequences identical to those identified in infected plants by HTS. The DNA sequences and the morphology of the organism did not match any known species. Here we present a new genus and species, Phytocercomonas venanatans, which is associated with chlorotic streak of sugarcane. Amplicon sequencing also supports that P. venanatans is associated with this disease. This is the first reported member from Cercomonadida showing a probable pathogenic association with higher plants.

Plant Rhizosphere Selection of Plasmodiophorid Lineages from Bulk Soil: The Importance of "Hidden" Diversity

Microbial communities closely associated with the rhizosphere can have strong positive and negative impacts on plant health and growth. We used a group-specific amplicon approach to investigate local scale drivers in the diversity and distribution of plasmodiophorids in rhizosphere/root and bulk soil samples from oilseed rape (OSR) and wheat agri-systems. Plasmodiophorids are plant- and stramenopile-associated protists including well known plant pathogens as well as symptomless endobiotic species. We detected 28 plasmodiophorid lineages (OTUs), many of them novel, and showed that plasmodiophorid communities were highly dissimilar and significantly divergent between wheat and OSR rhizospheres and between rhizosphere and bulk soil samples. Bulk soil communities were not significantly different between OSR and wheat systems. Wheat and OSR rhizospheres selected for different plasmodiophorid lineages. An OTU corresponding to Spongospora nasturtii was positively selected in the OSR rhizosphere, as were two genetically distinct OTUs. Two novel lineages related to Sorosphaerula veronicae were significantly associated with wheat rhizosphere samples, indicating unknown plant-protist relationships. We show that group-targeted eDNA approaches to microbial symbiont-host ecology reveal significant novel diversity and enable inference of differential activity and potential interactions between sequence types, as well as their presence.

Diversity of Cercomonad Species in the Phyllosphere and Rhizosphere of Different Plant Species with a Description of Neocercomonas epiphylla (Cercozoa, Rhizaria) a Leaf-Associated Protist

Cercomonads are among the most abundant and diverse groups of heterotrophic flagellates in terrestrial systems and show an affinity to plants. However, we still lack basic knowledge of plant-associated protists. We isolated 75 Cercomonadida strains from the phyllosphere and rhizosphere of plants from three functional groups: grasses (Poa sp.), legumes (Trifolium sp.) and forbs (Plantago sp.), representing 28 OTUs from the genera Cercomonas, Neocercomonas and Paracercomonas. The community composition differed clearly between phyllosphere and rhizosphere, but was not influenced by plant species identity. From these isolates we describe three novel cercomonad species including Neocercomonas epiphylla that was consistently and exclusively isolated from the phyllosphere. For each new species we provide a detailed morphological description as well as an 18S rDNA gene sequence as a distinct marker of species identity. Our data contribute to a better resolution of the systematics of cercomonads and their association with plants, by describing three novel species and adding gene sequences of 10 new cercomonad genotypes and of nine previously described species. In view of the functional importance of cercozoan communities in the phyllosphere and rhizosphere of plants, a more detailed understanding of their composition, function and predator-prey interactions are clearly required.

An Orphan Protist Quadricilia rotundata Finally Finds Its Phylogenetic Home in Cercozoa

Quadricilia rotundata is a heterotrophic flagellate with four flagella. However, because this species has no clear morphological characteristics or molecular data affiliating it with any known group, Q. rotundata has been treated as a protist incertae sedis, for a long time. Here, we established a clonal culture of Q. rotundata and sequenced its 18S rDNA sequence. Molecular phylogenetic analysis successfully placed Q. rotundata in an environmental clade within Cercozoa, which contributes to expand the morphological and species diversity within Cercozoa. We also discuss morphological evolution within Cercozoa based on this finding.

Environmental Sequencing Fills the Gap Between Parasitic Haplosporidians and Free-living Giant Amoebae

Class Ascetosporea (Rhizaria; Endomyxa) comprises many parasites of invertebrates. Within this group, recent group-specific environmental DNA (eDNA) studies have contributed to the establishment of the new order Mikrocytida, a new phylogeny and characterization of Paramyxida, and illuminated the diversity and distribution of haplosporidians. Here, we use general and lineage-specific PCR primers to investigate the phylogenetic "gap" between haplosporidians and their closest known free-living relatives, the testate amoeba Gromia and reticulate amoeba Filoreta. Within this gap are Paradinium spp. parasites of copepods, which we show to be highly diverse and widely distributed in planktonic and benthic samples. We reveal a robustly supported radiation of parasites, ENDO-3, comprised of Paradinium and three further clades (ENDO-3a, ENDO-3b and SPP). A further environmental group, ENDO-2, perhaps comprising several clades, branches between this radiation and the free-living amoebae. Early diverging haplosporidians were also amplified, often associated with bivalves or deep-sea samples. The general primer approach amplified an overlapping set of novel lineages within ENDO-3 and Haplosporida, whereas the group-specific primer strategy, targeted to amplify from the earliest known divergent haplosporidians to Gromia, generated greater sequence diversity across part of this phylogenetic range.

Kingdom Chromista and its eight phyla: a new synthesis emphasising periplastid protein targeting, cytoskeletal and periplastid evolution, and ancient divergences

In 1981 I established kingdom Chromista, distinguished from Plantae because of its more complex chloroplast-associated membrane topology and rigid tubular multipartite ciliary hairs. Plantae originated by converting a cyanobacterium to chloroplasts with Toc/Tic translocons; most evolved cell walls early, thereby losing phagotrophy. Chromists originated by enslaving a phagocytosed red alga, surrounding plastids by two extra membranes, placing them within the endomembrane system, necessitating novel protein import machineries. Early chromists retained phagotrophy, remaining naked and repeatedly reverted to heterotrophy by losing chloroplasts. Therefore, Chromista include secondary phagoheterotrophs (notably ciliates, many dinoflagellates, Opalozoa, Rhizaria, heliozoans) or walled osmotrophs (Pseudofungi, Labyrinthulea), formerly considered protozoa or fungi respectively, plus endoparasites (e.g. Sporozoa) and all chromophyte algae (other dinoflagellates, chromeroids, ochrophytes, haptophytes, cryptophytes). I discuss their origin, evolutionary diversification, and reasons for making chromists one kingdom despite highly divergent cytoskeletons and trophic modes, including improved explanations for periplastid/chloroplast protein targeting, derlin evolution, and ciliary/cytoskeletal diversification. I conjecture that transit-peptide-receptor-mediated 'endocytosis' from periplastid membranes generates periplastid vesicles that fuse with the arguably derlin-translocon-containing periplastid reticulum (putative red algal trans-Golgi network homologue; present in all chromophytes except dinoflagellates). I explain chromist origin from ancestral corticates and neokaryotes, reappraising tertiary symbiogenesis; a chromist cytoskeletal synapomorphy, a bypassing microtubule band dextral to both centrioles, favoured multiple axopodial origins. I revise chromist higher classification by transferring rhizarian subphylum Endomyxa from Cercozoa to Retaria; establishing retarian subphylum Ectoreta for Foraminifera plus Radiozoa, apicomonad subclasses, new dinozoan classes Myzodinea (grouping Colpovora gen. n., Psammosa), Endodinea, Sulcodinea, and subclass Karlodinia; and ranking heterokont Gyrista as phylum not superphylum.

High-throughput sequencing of microbial eukaryotes in Lake Baikal reveals ecologically differentiated communities and novel evolutionary radiations

We performed high-throughput 18S rDNA V9 region sequencing analyses of microeukaryote (protist) communities at seven sites with depths ranging from 0 to 1450 m in the southern part of Lake Baikal. We show that microeukaryotic diversity differed according to water column depth and sediment depth. Chrysophytes and perkinsids were diverse in subsurface samples, novel radiations of petalomonads and Ichthyobodo relatives were found in benthic samples, and a broad range of divergent OTUs were detected in deep subbenthic samples. Members of clades usually associated with marine habitats were also detected, including syndineans for the first time in freshwater systems. Fungal- and cercozoan-specific c. 1200 bp amplicon clone libraries also revealed many novel lineages in both planktonic and sediment samples at all depths, a novel radiation of aphelids in shallower benthic samples, and partitioning of sarcomonad lineages in shallow vs deep benthic samples. Putative parasitic lineages accounted for 12.4% of overall reads, including a novel radiation of Ichthyobodo (fish parasite) relatives. Micrometazoans were also analysed, including crustaceans, rotifers and nematodes. The deepest (>1000 m) subsurface sediment samples harboured some highly divergent sequence types, including heterotrophic flagellates, parasites, putative metazoans and sequences likely representing organisms originating from higher up in the water column.

New barcoded primers for efficient retrieval of cercozoan sequences in high-throughput environmental diversity surveys, with emphasis on worldwide biological soil crusts

We describe the performance of a new metabarcoding approach to investigate the environmental diversity of a prominent group of widespread unicellular organisms, the Cercozoa. Cercozoa is an immensely large group of protists, and although it may dominate in soil and aquatic ecosystems, its environmental diversity remains undersampled. We designed PCR primers targeting the hypervariable region V4 of the small subunit ribosomal RNA (SSU or 18S) gene, which is the recommended barcode marker for Cercozoa. The length of the amplified fragment (c. 350 bp) is suitable for Illumina MiSeq, the most cost-effective platform for molecular environmental surveys. We provide barcoded primers, an economical alternative to multiple libraries for multiplex sequencing of over a hundred samples. In silico, our primers matched 68% of the cercozoan sequences of the reference database and performed better than previously proposed new-generation sequencing primers. In mountain grassland soils and in biological soil crusts from a variety of climatic regions, we were able to detect cercozoan sequences encompassing nearly the whole range of the phylum. We obtained 901 operational taxonomic units (OTUs) at 97% similarity threshold from 26 samples, with c. 50,000 sequences per site, and only 8% of noncercozoan sequences. We could report a further increase in the diversity of Cercozoa, as only 43% of the OTUs were 97%-100% similar to any known sequence. Our study thus provides an advanced tool for cercozoan metabarcoding and to investigate their diversity and distribution in the environment.

Single Cell Transcriptomics, Mega-Phylogeny, and the Genetic Basis of Morphological Innovations in Rhizaria

The innovation of the eukaryote cytoskeleton enabled phagocytosis, intracellular transport, and cytokinesis, and is largely responsible for the diversity of morphologies among eukaryotes. Still, the relationship between phenotypic innovations in the cytoskeleton and their underlying genotype is poorly understood. To explore the genetic mechanism of morphological evolution of the eukaryotic cytoskeleton, we provide the first single cell transcriptomes from uncultured, free-living unicellular eukaryotes: the polycystine radiolarian Lithomelissa setosa (Nassellaria) and Sticholonche zanclea (Taxopodida). A phylogenomic approach using 255 genes finds Radiolaria and Foraminifera as separate monophyletic groups (together as Retaria), while Cercozoa is shown to be paraphyletic where Endomyxa is sister to Retaria. Analysis of the genetic components of the cytoskeleton and mapping of the evolution of these on the revised phylogeny of Rhizaria reveal lineage-specific gene duplications and neofunctionalization of α and β tubulin in Retaria, actin in Retaria and Endomyxa, and Arp2/3 complex genes in Chlorarachniophyta. We show how genetic innovations have shaped cytoskeletal structures in Rhizaria, and how single cell transcriptomics can be applied for resolving deep phylogenies and studying gene evolution in uncultured protist species.

Phylogeny and Systematics of Leptomyxid Amoebae (Amoebozoa, Tubulinea, Leptomyxida)

We describe four new species of Flabellula, Leptomyxa and Rhizamoeba and publish new SSU rRNA gene and actin gene sequences of leptomyxids. Using these data we provide the most comprehensive SSU phylogeny of leptomyxids to date. Based on the analyses of morphological data and results of the SSU rRNA gene phylogeny we suggest changes in the systematics of the order Leptomyxida (Amoebozoa: Lobosa: Tubulinea). We propose to merge the genera Flabellula and Paraflabellula (the genus Flabellula remains valid by priority rule). The genus Rhizamoeba is evidently polyphyletic in all phylogenetic trees; we suggest retaining the generic name Rhizamoeba for the group unifying R. saxonica, R.matisi n. sp. and R. polyura, the latter remains the type species of the genus Rhizamoeba. Based on molecular and morphological evidence we move all remaining Rhizamoeba species to the genus Leptomyxa. New family Rhizamoebidae is established here in order to avoid paraphyly of the family Leptomyxidae. With the suggested changes both molecular and morphological systems of the order Leptomyxida are now fully congruent to each other.

Polyphyly in the Thecate Amoeba Genus Lecythium (Chlamydophryidae, Tectofilosida, Cercozoa), Redescription of its Type Species L. hyalinum, Description of L. jennyae sp. nov. and the Establishment of Fisculla gen. nov. and Fiscullidae fam. nov

Although testate amoebae have attracted great interest of protistologists for more than a century, some groups, especially those with a hyaline, organic test (=theca) are still poorly known. One of those is the genus Lecythium Hertwig et Lesser, 1874. Only recently Lecythium spp. were characterized by morphological and molecular means, but data on the type species Lecythium hyalinum Hertwig et Lesser, 1874, was still lacking. In this study, we screened for L. hyalinum in freshwater samples of Germany and the Netherlands. Four different isolates of L. hyalinum and one novel species were cultured and characterized by light microscopy. Phylogenetic analyses based on the small ribosomal subunit (SSU) RNA gene show that the genus Lecythium forms two robust clades, one forming a sister group to the Rhizaspididae/Pseudodifflugiidae clade (Tectofilosida), the other branching within 'Novel Clade 4' (Tectofilosida). We untangle this polyphyly by establishing Fisculla gen. nov. and the Fiscullidae fam. nov. for the former of these two clades.

The Large Subunit rDNA Sequence of Plasmodiophora brassicae Does not Contain Intra-species Polymorphism

Clubroot disease caused by Plasmodiophora brassicae is one of the most important diseases of cultivated brassicas. P. brassicae occurs in pathotypes which differ in the aggressiveness towards their Brassica host plants. To date no DNA based method to distinguish these pathotypes has been described. In 2011 polymorphism within the 28S rDNA of P. brassicae was reported which potentially could allow to distinguish pathotypes without the need of time-consuming bioassays. However, isolates of P. brassicae from around the world analysed in this study do not show polymorphism in their LSU rDNA sequences. The previously described polymorphism most likely derived from soil inhabiting Cercozoa more specifically Neoheteromita-like glissomonads. Here we correct the LSU rDNA sequence of P. brassicae. By using FISH we demonstrate that our newly generated sequence belongs to the causal agent of clubroot disease.

Hyperspora aquatica n.gn., n.sp. (Microsporidia), hyperparasitic in Marteilia cochillia (Paramyxida), is closely related to crustacean-infecting microspordian taxa

The Paramyxida, closely related to haplosporidians, paradinids, and mikrocytids, is an obscure order of parasitic protists within the class Ascetosporea. All characterized ascetosporeans are parasites of invertebrate hosts, including molluscs, crustaceans and polychaetes. Representatives of the genus Marteilia are the best studied paramyxids, largely due to their impact on cultured oyster stocks, and their listing in international legislative frameworks. Although several examples of microsporidian hyperparasitism of paramyxids have been reported, phylogenetic data for these taxa are lacking. Recently, a microsporidian parasite was described infecting the paramyxid Marteilia cochillia, a serious pathogen of European cockles. In the current study, we investigated the phylogeny of the microsporidian hyperparasite infecting M. cochillia in cockles and, a further hyperparasite, Unikaryon legeri infecting the digenean Meiogymnophallus minutus, also in cockles. We show that rather than representing basally branching taxa in the increasingly replete Cryptomycota/Rozellomycota outgroup (containing taxa such as Mitosporidium and Paramicrosoridium), these hyperparasites instead group with other known microsporidian parasites infecting aquatic crustaceans. In doing so, we erect a new genus and species (Hyperspora aquatica n. gn., n.sp.) to contain the hyperparasite of M. cochillia and clarify the phylogenetic position of U. legeri. We propose that in both cases, hyperparasitism may provide a strategy for the vectoring of microsporidians between hosts of different trophic status (e.g. molluscs to crustaceans) within aquatic systems. In particular, we propose that the paramyxid hyperparasite H. aquatica may eventually be detected as a parasite of marine crustaceans. The potential route of transmission of the microsporidian between the paramyxid (in its host cockle) to crustaceans, and, the 'hitch-hiking' strategy employed by H. aquatica is discussed.