Midgut microbiota of Pyrrhocoris apterus (European Firebug Metagenome. insect gut metagenome

Symbiotic bacteria often play an essential nutritional role for insects, thereby allowing them to exploit novel food sources and expand into otherwise inaccessible ecological niches. Although many insects are inhabited by complex microbial communities, most studies on insect mutualists so far have focused on single endosymbionts and their interactions with the host. Here we provide a comprehensive characterization of the gut microbiota of the red firebug (Pyrrhocoris apterus, Hemiptera, Pyrrhocoridae), a model organism for physiological and endocrinological research. A combination of several culture-independent techniques (454-pyrosequencing, quantitative PCR and cloning/sequencing) revealed a diverse community of likely transient bacterial taxa in the mid-gut regions M1, M2 and M4. However, the completely anoxic M3 region harbored a distinct microbiota consisting of facultative and obligate anaerobes including Actinobacteria (Coriobacterium glomerans and Gordonibacter sp.), Firmicutes (Clostridium sp. and Lactococcus lactis), and Proteobacteria (Klebsiella sp., and a previously undescribed Rickettsiales bacterium). Characterization of the M3 microbiota in different life stages of P. apterus indicated that the symbiotic bacterial community is transmitted vertically and becomes well defined between the second and third nymphal instar, which coincides with the initiation of feeding. Comparing the midgut M3 microbial communities of P. apterus individuals from five different populations and after feeding on three different diets revealed that the community composition is qualitatively and quantitatively very stable, with the six predominant taxa being consistently abundant. Our findings suggest that the firebug mid-gut microbiota constitutes a functionally important and possibly coevolved symbiotic community.