Phagocytosis underpins the biotrophic lifestyle of intracellular parasites in the class Phytomyxea (Rhizaria).

Phytomyxea are intracellular biotrophic parasites infecting plants and stramenopiles, including the agriculturally impactful Plasmodiophora brassicae and the brown seaweed pathogen Maullinia ectocarpii. They belong to the clade Rhizaria, where phagotrophy is the main mode of nutrition. Phagocytosis is a complex trait of eukaryotes, well documented for free-living unicellular eukaryotes and specific cellular types of animals. Data on phagocytosis in intracellular, biotrophic parasites are scant. Phagocytosis, where parts of the host cell are consumed at once, is seemingly at odds with intracellular biotrophy. Here we provide evidence that phagotrophy is part of the nutritional strategy of Phytomyxea, using morphological and genetic data (including a novel transcriptome of M. ectocarpii). We document intracellular phagocytosis in P. brassicae and M. ectocarpii by transmission electron microscopy and fluorescent in situ hybridization. Our investigations confirm molecular signatures of phagocytosis in Phytomyxea and hint at a small specialized subset of genes used for intracellular phagocytosis. Microscopic evidence confirms the existence of intracellular phagocytosis, which in Phytomyxea targets primarily host organelles. Phagocytosis seems to coexist with the manipulation of host physiology typical of biotrophic interactions. Our findings resolve long debated questions on the feeding behaviour of Phytomyxea, suggesting an unrecognized role for phagocytosis in biotrophic interactions.

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.

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.

Emerging from the ice-fungal communities are diverse and dynamic in earliest soil developmental stages of a receding glacier.

We used amplicon sequencing and isolation of fungi from in-growth mesh bags to identify active fungi in three earliest stages of soil development (SSD) at a glacier forefield (0-3, 9-14, 18-25 years after retreat of glacial ice). Soil organic matter and nutrient concentrations were extremely low, but the fungal diversity was high [220 operational taxonomic units (OTUs)/138 cultivated OTUs]. A clear successional trend was observed along SSDs, and species richness increased with time. Distinct changes in fungal community composition occurred with the advent of vascular plants. Fungal communities of recently deglaciated soil are most distinctive and rather similar to communities typical for cryoconite or ice. This indicates melting water as an important inoculum for native soil. Moreover, distinct seasonal differences were detected in fungal communities. Some fungal taxa, especially of the class Microbotryomycetes, showed a clear preference for winter and early SSD. Our results provide insight into new facets regarding the ecology of fungal taxa, for example, by showing that many fungal taxa might have an alternative, saprobial lifestyle in snow-covered, as supposed for a few biotrophic plant pathogens of class Pucciniomycetes. The isolated fungi include a high proportion of unknown species, which can be formally described and used for experimental approaches.