Environ Microbiol Rep. 2010 Aug;2(4):554-9. doi: 10.1111/j.1758-2229.2009.00124.x. Epub 2010 Jan 05.

Putatively free-living 'Endomicrobia'- ancestors of the intracellular symbionts of termite gut flagellates?.

Environmental microbiology reports

Wakako Ikeda-Ohtsubo, Nicolas Faivre, Andreas Brune

PMID: 23766225 DOI: 10.1111/j.1758-2229.2009.00124.x

Abstract

Endomicrobia represent a candidate class in the Elusimicrobia phylum (formerly Termite Group 1) and were originally described as obligate intracellular symbionts of gut flagellates in lower termites. However, 16S rRNA gene sequences of Endomicrobia have been detected also in the gut of insects that do not possess such flagellates, e.g. higher termites and cockroaches. When we eliminated the large gut flagellates of Reticulitermes santonensis by feeding a starch diet, we discovered novel lineages of Endomicrobia that were hitherto undetected in normally faunated specimens. The new phylotypes are clearly separated from the endosymbionts of gut flagellates and fall into the radiation of those from flagellate-free insects. Comprehensive phylogenetic analysis documented that Endomicrobia comprise an apical cluster of endosymbionts that is not necessarily monophyletic and several apparently basal lineages that include bacteria present in the gut of defaunated lower termites, the naturally flagellate-free guts of higher termites and scarab beetle larvae, and in the cow rumen. We propose that these lineages represent hitherto undetected free-living Endomicrobia that share a common ancestor with the intracellular symbionts.

© 2010 Society for Applied Microbiology and Blackwell Publishing Ltd.

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