The Gut Commensal Microbiome of Is Modified by the Endosymbiont .

Endosymbiotic bacteria and the gut microbiome have independently been shown to affect several aspects of insect biology, including reproduction, development, life span, stem cell activity, and resistance to human pathogens, in insect vectors. This work shows that bacteria, which reside mainly in the fly germline, affect the microbial species present in the fly gut in a lab-reared strain. hosts two main genera of commensal bacteria- and . -infected flies have significantly reduced titers of . Sampling of the microbiome of axenic flies fed with equal proportions of both bacteria shows that the presence of bacteria is a significant determinant of the composition of the microbiome throughout fly development. However, this effect is host genotype dependent. To investigate the mechanism of microbiome modulation, the effect of bacteria on Imd and reactive oxygen species pathways, the main regulators of immune response in the fly gut, was measured. The presence of bacteria does not induce significant changes in the expression of the genes for the effector molecules in either pathway. Furthermore, microbiome modulation is not due to direct interaction between bacteria and gut microbes. Confocal analysis shows that bacteria are absent from the gut lumen. These results indicate that the mechanistic basis of the modulation of composition of the microbiome by bacteria is more complex than a direct bacterial interaction or the effect of bacteria on fly immunity. The findings reported here highlight the importance of considering the composition of the gut microbiome and host genetic background during -induced phenotypic studies and when formulating microbe-based disease vector control strategies. bacteria are intracellular bacteria present in the microbiome of a large fraction of insects and parasitic nematodes. They can block mosquitos' ability to transmit several infectious disease-causing pathogens, including Zika, dengue, chikungunya, and West Nile viruses and malaria parasites. Certain extracellular bacteria present in the gut lumen of these insects can also block pathogen transmission. However, our understanding of interactions between and gut bacteria and how they influence each other is limited. Here we show that the presence of strain Mel changes the composition of gut commensal bacteria in the fruit fly. Our findings implicate interactions between bacterial species as a key factor in determining the overall composition of the microbiome and thus reveal new paradigms to consider in the development of disease control strategies.