Midgut microbiota of Dysdercus fasciatus. insect gut metagenome

Actinobacteria engage in defensive symbioses with several insect taxa, but reports of nutritional contributions to their hosts have been exceptionally rare. Cotton stainers (Dysdercus fasciatus) and red firebugs (Pyrrhocoris apterus) (both Hemiptera, Pyrrhocoridae) harbor the actinobacterial symbionts Coriobacterium glomerans and Gordonibacter as well as Firmicutes (Clostridium and Lactococcus) and Proteobacteria (Klebsiella and a Rickettsiales bacterium) in the M3 region of their mid-gut. We combined experimental manipulation with community-level analyses to elucidate the function of the gut symbionts in both pyrrhocorid species. Elimination of symbionts by egg-surface sterilization resulted in significantly higher mortality and reduced growth rates, demonstrating that the microbial community plays an important role for host nutrition. Fitness of symbiont-deprived bugs could be completely restored by re-infection with the original microbiota, while reciprocal cross-infections of microbial communities across both pyrrhocorid species only partially rescued fitness, indicating a high degree of host-symbiont specificity. Exhaustive community-level analyses by quantitative PCRs targeting the dominant bacterial strains allowed us to link the observed fitness effects exclusively to the abundance of the two actinobacterial symbionts. Thus, the nutritional mutualism with Actinobacteria may have represented a key evolutionary innovation that contributed significantly to the ecological success of the economically important group of pyrrhocorid bugs. Midgut microbial community of Dysdercus fasciatus sequenced using 454 amplicon pyrosequencing.