Selected gut bacteria promote mosquito larval growth through the regulation of ionic microenvironment and protease expression

The anterior midgut of mosquito larvae harbors microbiota. Besides, the hyperalkaline (pH∼10-11) anterior midgut also provides an optimal ionic microenvironment for protein digestion. Although gut microbiota is known to promote larval growth and development, the underlying host-microbe mechanisms remain less understood. Using the <i>Aedes albopictus</i> axenic-gnotobiotic model, we show that anterior midgut alkalinization necessitates colonization by "live" bacteria belonging to selected genera. Results of our bacteriophage-mediated gut bacteria decolonization studies suggest that the colonizing bacteria also mediate the expression of crucial larval proteases. Additionally, the colonizing bacteria contribute a significant proportion of proteases (including serine proteases, aminopeptidases, etc.) to the larval gut, which are crucial for the digestion of dietary proteins. Collectively, these findings reveal that specific members of the gut microbiota promote larval growth and development by facilitating larval protein metabolism through modulation of the midgut microenvironment. These findings may have important implications for the development of targeted vector-control strategies.