Gut Immune Pathway Suppresses Host Development-Promoting Effects of Acetic Acid Bacteria.

The physiology of most organisms, including , is heavily influenced by their interactions with certain types of commensal bacteria. and , two of the most representative commensal bacteria, have stimulatory effects on host larval development and growth. However, how these effects are related to host immune activity remains largely unknown. Here, we show that the development-promoting effects of commensal bacteria are suppressed by host immune activity. Mono-association of germ-free larvae with stimulated larval development, which was accelerated when host immune deficiency (IMD) pathway genes were mutated. This phenomenon was not observed in the case of mono-association with . Moreover, the mutation of Toll pathway, which constitutes the other branch of the immune pathway, did not accelerate -stimulated larval development. The mechanism of action of the IMD pathway-dependent effects of did not appear to involve previously known host mechanisms and bacterial metabolites such as gut peptidase expression, acetic acid, and thiamine, but appeared to involve . These findings may shed light on the interaction between the beneficial effects of commensal bacteria and host immune activity.