High diversity and isolated distribution of aquatic heterotrophic protists in salars of the Atacama Desert at different salinities.

The species richness of eukaryotes in the hypersaline environment is generally thought to be low. However, recent studies showed a high degree of phylogenetic novelty at these extreme conditions with variable chemical parameters. These findings call for a more thorough look into the species richness of hypersaline environments. In this study, various hypersaline lakes (salars, 1-348 PSU) as well as further aquatic ecosystems of northern Chile were investigated regarding diversity of heterotrophic protists by metabarcoding studies of surface water samples. Investigations of genotypes of 18S rRNA genes showed a unique community composition in nearly each salar and even among different microhabitats within one salar. The genotype distribution showed no clear connection to the composition of main ions at the sampling sites, but protist communities from similar salinity ranges (either hypersaline, hyposaline or mesosaline) clustered together regarding their OTU composition. Salars appeared to be fairly isolated systems with only little exchange of protist communities where evolutionary lineages could separately evolve.

Revision of the phylogeny of Placididea (Stramenopiles): Molecular and morphological diversity of novel placidid protists from extreme aquatic environments.

Recent studies suggested that the diversity of microbial eukaryotes in hypersaline environments is widely underestimated. Placidids are a group of heterotrophic stramenopile flagellates that are frequently found in these environments, but up to now only very few species were isolated and fully described, mostly from marine or brackish water sites. In this study, we extend the known diversity of Placididea by three new genera (Allegra, Haloplacidia, and Placilonga) compromising nine new species, isolated from athalassic, mostly hypersaline environments (Allegra dunaii, Allegra atacamiensis, Allegra hypersalina, Haloplacidia cosmopolita, Suigetsumonas keniensis) and marine waters (Placilonga atlantica, Placidia azorensis, Placidia abyssalis, Wobblia pacifica) including a description of their morphology and molecular phylogeny. In total, 36 strains were comparatively analysed. Studies from athalassic waters revealed an especially high number of different genotypes. A multigene analysis based on a ten genes dataset revealed a clear separation into marine, athalassic and brackish water clades. Several representatives were found to cope with hypersaline conditions from 20 to 250 PSU, even up to 284 PSU, suggesting that they may form a halotolerant group.