Pei191 is the first isolate from a novel bacterial phylum, comprising endosymbionts of cellulose-degrading termite gut protozoa (Endomicrobia) and presumably free-living bacteria from various environments. Together with the genome of the endosymbiont Canditatus Endomicrobium trichonymphae (CET), the genome of this free-living representative will provide important information on the biology of bacteria in this novel phylum, their energy metabolism, and the roles of the symbionts in carbon sequestration and in the tripartite symbiosis with protozoan and insect hosts.