<em>Blattella germanica</em> Selects Microbiota Taxa from Feces and Environmental Inputs

Cockroaches display a double symbiosis: an obligate intracellular one with Blattabacterium cuenoti, and a complex extracellular intestinal non-vertically transmitted microbiota, that may be affected by horizontally transmitted factors. Four experiments using 16S rRNA gene amplicon sequencing analyzed the microbiota of the hindgut and feces of adult cockroaches to understand the influence of the environment, feces, and host genetic background on hindgut microbiota acquisition and development. We observed that sample type, rearing conditions, and host influenced microbiota composition. Furthermore, the induction of germ-free cockroaches placed in non-sterile conditions had a greater impact on microbiota than rearing conditions, also showing that in absence of fecal inputs the cockroach gut microbiota is strongly diminished. Moreover, when exploring fecal microbiota differences between three cockroach species, the greatest divergence was found between Periplaneta americana and Blattella germanica, with Blatta orientalis being placed in an intermediate position. Therefore, P. americana was selected for fecal transplantation on B. germanica. This transplantation experiment indicates that host species clearly influence intestinal bacterial selection, limiting full integration of donor-derived communities. Overall, these results suggest that beyond other factors the host species had the strongest influence on shaping the cockroach gut microbiota.