Genetic drift and host-adaptive features likely underlie cladogenesis of insect-associated Lachnospiraceae

Phylogenetic and functional group analysis of the genomes of anaerobic bacteria isolated from Periplaneta americana digestive tracts suggest that they represent novel Lachnospiraceae genera. PAL113 and PAL227 isolate genomes encoded short-chain fatty acid biosynthetic pathways and plant fiber and chitin catabolism and other carbohydrate utilization genes common in related Lachnospiraceae species, yet the presence of operons containing flagellar assembly pathways were among several distinguishing features. In general, PAL113 and PAL227 isolates encode an array of gene products that would enable them to thrive in the insect gut environment and potentially play a role in host diet processing. We hypothesize that cladogenesis of these isolates could be due to their oxygen sensitivity, reliance upon the host for dispersal and genetic drift and not necessarily as a result of an ongoing mutualism.