Ontogeny of the gut microbiota in the cockroach Blattella germanica

Bacterial symbionts of insects have many metabolic activities that are absent in their hosts, and vice versa. Blattabacterium lives inside the fat body cells of most of the cockroaches and plays an important role in nitrogen recycling. These insects also carry a variety of exosymbionts attached to the gastrointestinal walls, which collaborate in digestion and act as a barrier against colonization by pathogens, among other functions. For this work, the cockroach Blattella germanica was chosen in part by its importance as an indoor pest and also, because of its experimental convenience due to its short life cycle. The mode of acquisition of the gut exosymbionts is unknown, as well as the dynamics of their ecological succession across the life cycle of the insect. We have characterized the intestinal flora by different approaches. First, electron scanning microscopy confirmed the presence of a bacterial biofilm exclusively in the hindgut. qPCR revealed that the bacterial load in the gut increases with age. Pyrosequencing the hyper-variable regions V1-V3 of the 16S rRNA genes present in the guts of all the nymphal instars and adults of B. germanica revealed that the microbial composition is stage-specific through the development of the insect. Last, analysis of the embryos demonstrated that Blattabacterium is the only symbiont inherited maternally via the eggs, running out to elucidate the mode of adquisition of the intestinal microbiota.