Prokaryotic diversity was studied in the planktonic communities of six Sol-Iletsk lakes (Orenburg oblast, Russia) varying in salinity level using the Illumina technology of high-throughput...

Climate change, desertification, salinisation of soils and the changing hydrology of the Earth are creating or modifying microbial habitats at all scales including the oceans, saline groundwaters and brine lakes. In environments that are saline or hypersaline, the biodegradation of recalcitrant plant and animal polysaccharides can be inhibited by salt‐induced microbial stress and/or by limitation of the metabolic capabilities of halophilic microbes. We recently demonstrated that the chitinolytic haloarchaeon Halomicrobium can serve as the host for an ectosymbiont, nanohaloarchaeon ‘ Candidatus Nanohalobium constans’. Here, we consider whether nanohaloarchaea can benefit from the haloarchaea‐mediated degradation of xylan, a major hemicellulose component of wood. Using samples of natural evaporitic brines and anthropogenic solar salterns, we describe genome‐inferred trophic relations in two extremely halophilic xylan‐degrading three‐member consortia. We succeeded in genome assembly and closure for all members of both xylan‐degrading cultures and elucidated the respective food chains within these consortia. We provide evidence that ectosymbiontic nanohaloarchaea is an active ecophysiological component of extremely halophilic xylan‐degrading communities (although by proxy ) in hypersaline environments. In each consortium, nanohaloarchaea occur as ectosymbionts of Haloferax , which in turn act as scavenger of oligosaccharides produced by xylan‐hydrolysing Halorhabdus . We further obtained and characterised the nanohaloarchaea–host associations using microscopy, multi‐omics and cultivation approaches. The current study also doubled culturable nanohaloarchaeal symbionts and demonstrated that these enigmatic nano‐sized archaea can be readily isolated in binary co‐cultures using an appropriate enrichment strategy. We discuss the implications of xylan degradation by halophiles in biotechnology and for the United Nation's Sustainable Development Goals.

The influence of microalgae on the formation of associated prokaryotic assemblages in halophilic microbial communities is currently underestimated. The aim of this study was to characterize shifts in prokaryotic assemblages of halophilic microalgae upon their transition to laboratory cultivation. Monoalgal cultures belonging to the classes Chlorodendrophyceae, Bacillariophyceae, Trebouxiophyceae, and Chlorophyceae were isolated from habitats with intermediate salinity, about 100 g/L, nearby Elton Lake (Russia). Significant changes were revealed in the structure of algae-associated prokaryotic assemblages, indicating that microalgae supported sufficiently diverse and even communities of prokaryotes. Despite some similarities in their prokaryotic assemblages, taxon-specific complexes of dominant genera were identified for each microalga species. These complexes were most different among Alphaproteobacteria, likely due to their close association with microalgae. Other taxon-specific bacteria included members of phylum Verrucomicrobiota (Coraliomargarita in assemblages of Navicula sp.) and class Gammaproteobacteria (Salinispirillum in microbiomes of A. gracilis). After numerous washings of algal cells, only alphaproteobacteria Marivibrio remained in all assemblages of T. indica, likely due to a firm attachment to the microalgae cells. Our results may be useful for further efforts to develop technologies applied for industrial cultivation of halophilic microalgae and for developing approaches to obtain new prokaryotes with a microalgae-associated lifestyle.

Lake Kislo-Sladkoe is a stratified water body partly isolated from the White Sea. Perennial meromixis in the lake irregularly alternates with mixing events. Taking into account that the protists of Arctic coastal stratified water bodies are understudied, we evaluated for the first time the vertical structure, species richness, and diversity of protists assigned to different taxonomic groups in Lake Kislo-Sladkoe using light, luminescent, and scanning electron microscopy. To test the research hypothesis that a mixing event affects the vertical stratification and species composition of protists in a stratified lake, we compared the protist communities of Lake Kislo-Sladkoe in two extremely different states: strong meromixis vs. full vertical mixing. A total of 97 morphologically distinct phototrophic, heterotrophic, and mixotrophic protists were revealed with the most diverse supertaxa SAR (59), Obazoa (9), and Excavates (14). The hidden diversity of protists (43 species) was a bit less than the active diversity (54 species). A taxonomic list and micrographs of cells for the observed protists are provided. The majority of species revealed are cosmopolitan or widespread in the northern sea waters. The vertical patterns of protist communities were absolutely different in 2018 and 2021. In July 2018, clearly distinct protist communities inhabited different layers of the lake. Bloom of cryptophyte Rhodomonas cf. baltica was detected in chemocline, whereas the maximum density of its grazers was observed in adjacent layers, mainly dinoflagellates Gymnodinium sp. and Scrippsiella trochoidea, as well as a ciliate Prorodon sp. In 2021 due to the recent mixing of lake and seawater, there were no distinct communities in the water column except the superficial 0–1 m layer of fresh water.

The artificial solar saltwork fields of Hon Khoi are important industrial and biodiversity resources in southern Vietnam. Most hypersaline environments in this area are characterized by saturated salinity, nearly neutral pH, intense ultraviolet radiation, elevated temperatures and fast desiccation processes. However, the extreme halophilic prokaryotic communities associated with these stressful environments remain uninvestigated. To fill this gap, a metabarcoding approach was conducted to characterize these communities by comparing them with solar salterns in northern Vietnam as well as with Italian salterns. Sequencing analyses revealed that the multiple reuses of crystallization ponds apparently create significant perturbations and structural instability in prokaryotic consortia. However, some interesting features were noticed when we examined the diversity of ultra-small prokaryotes belonging to Patescibacteria and DPANN Archaea. Surprisingly, we found at least five deeply branched clades, two from Patescibacteria and three from DPANN Archaea, which seem to be quite specific to Hon Khoi saltwork fields ecosystem and can be considered as a part of biogeographical connotation. Further studies are needed to characterize these uncultivated taxa, to isolate and cultivate them, which will allow us to elucidate their ecological role in these hypersaline habitats and to explore their biotechnological and biomedical potential.

The artificial solar saltworks fields of Hon Khoi are important industrial and biodiversity resources in southern Vietnam. Most hypersaline environments in this area are characterized by saturated salinity, nearly neutral pH, intense ultraviolet radiation, elevated temperatures and fast desiccation processes. However, the extremely halophilic prokaryotic communities associated with these stressful environments remain uninvestigated. To fill this gap, a metabarcoding approach was conducted to characterize these communities by comparing them with solar salterns in northern Vietnam as well as with the Italian salterns of Motya and Trapani. Sequencing analyses revealed that the multiple reuses of crystallization ponds apparently create significant perturbations and structural instability in prokaryotic consortia. However, some interesting features were noticed when we examined the diversity of ultra-small prokaryotes belonging to Patescibacteria and DPANN Archaea. Surprisingly, we found at least five deeply branched clades, two from Patescibacteria and three from DPANN Archaea, which seem to be quite specific to the Hon Khoi saltworks field ecosystem and can be considered as a part of biogeographical connotation. Further studies are needed to characterize these uncultivated taxa, to isolate and cultivate them, which will allow us to elucidate their ecological role in these hypersaline habitats and to explore their biotechnological and biomedical potential.