The ciliate Stentor coeruleus microbiome. The ciliate Stentor coeruleus microbiome

Microbiomes of multicellular organisms are the hot topic in microbiology and physiology, while only few studies addressed bacterial communities associated with protists. Protists are widespread in all environments and can be colonized by plethora of different bacteria, including also human pathogens. The aim of this study was to characterize the prokaryotic community associated with the sessile ciliate Stentor coeruleus. 16S rRNA gene metabarcoding was performed on single cells of S. coeruleus and on their environment, water from the sewage stream. Our results showed that the prokaryotic community composition differed significantly between Stentor cells and their environment. At the same time, the microbiome was rather similar between all ciliate specimens analyzed, and it was composed mainly by representatives of bacterial genera which include also potential human pathogens and commensals, such as Neisseria, Streptococcus, Capnocytophaga, and Veillonella. Numerous 16S rRNA gene contigs belonged to cosmopolitan endosymbiont “Candidatus Megaira polyxenophila”. Our data suggest that each ciliate cell can be considered as an ecological microniche harboring diverse prokaryotic organisms. Possible benefits for persistence and transmission in nature for bacteria associated with protists are discussed. Our results support the hypothesis that ciliates play the role of natural reservoirs for opportunistic and pathogenic bacteria.