Blattella germanica Selects Microbiota Taxa from Feces and Environmental Inputs

Cockroaches display a double symbiosis: an obligate intracellular one with Blattabacterium spp., and a complex extracellular non-vertically transmitted gut microbiota, that may be affected by horizontally transmitted factors. Four experiments using 16S rRNA gene amplicon sequencing were conducted to analyze the microbiota of the hindgut and feces of adult cockroaches. They aimed to understand the influence of the environment and feces on the acquisition and development of the hindgut microbiota. We observed that sample type (hindgut vs. feces), rearing conditions (environment, i.e., place and diet), coprophagy, and host influenced microbiota composition. Cockroaches initially germ-free, placed in non-sterile conditions and with blocked parental coprophagy, were unable to develop the normal microbiota of the control population, demonstrating that coprophagy is essential for acquiring a normal microbiota. This also showed that, in the absence of parental fecal input, the cockroach gut microbiota is strongly diminished. Moreover, when exploring fecal microbiota differences among three cockroach species, the greatest divergence was observed between Periplaneta americana and Blattella germanica, with Blatta orientalis occupying an intermediate position. Therefore, P. americana was selected for fecal transplantation on B. germanica. This transplantation experiment indicates that different species select different gut microbes, and that even when they receive feces from other species, only some of those bacteria are retained. Overall, these results suggest that beyond other factors, the host species had the strongest influence on shaping the cockroach gut microbiota.