Colonial choanoflagellate isolated from Mono Lake harbors a microbiome

Choanoflagellates offer key insights into bacterial influences on the origin and earlyevolution of animals. Here we report the isolation and characterization of a newcolonial choanoflagellate species, Barroeca monosierra, that, unlike previouslycharacterized species, harbors a stable microbiome. B. monosierra was isolated fromMono Lake, California and forms large spherical colonies that are more than an orderof magnitude larger than those formed by the closely related Salpingoeca rosetta. Bydesigning fluorescence in situ hybridization probes from metagenomic sequences, wefound that B. monosierra colonies are colonized by members of the halotolerant andclosely related Saccharospirillaceae and Oceanospirillaceae, as well as purple sulfurbacteria (Ectothiorhodospiraceae) and non-sulfur Rhodobacteraceae. This relativelysimple microbiome in a close relative of animals presents a new experimental modelfor investigating the evolution of stable interactions among eukaryotes and bacteria.