The Cultivation of Halophilic Microalgae Shapes the Structure of Their Prokaryotic Assemblages

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 <i>Alphaproteobacteria</i>, likely due to their close association with microalgae. Other taxon-specific bacteria included members of phylum <i>Verrucomicrobiota</i> (<i>Coraliomargarita</i> in assemblages of <i>Navicula</i> sp.) and class <i>Gammaproteobacteria (Salinispirillum</i> in microbiomes of <i>A. gracilis</i>). After numerous washings of algal cells, only alphaproteobacteria <i>Marivibrio</i> remained in all assemblages of <i>T. indica</i>, 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.