Select Gut Bacteria Promote Mosquito Larval Growth by Contributing Protease Activity and Optimal Ionic Microenvironment for Protein Digestion

The unique pH profile of mosquito larval midgut including the highly alkaline anterior midgut (AMG) and its significance in digestive physiology has been known for a long time. More recently, metagenomic association studies have shown that diverse assemblage of bacteria (microbiota) present in the gut influence larval nutrition, growth, development, and several other physiological processes. However, the precise functional mechanisms of these host-microbe interactions remain poorly understood. In this research, we studied the functional significance of gut associated bacteria in larval growth utilizing Aedes albopictus axenic/ gnotobiotic model. Results of our study demonstrate that, for AMG alkalinization, concurrent presence of Carbonic Anhydrase (CA) activity and live bacteria is essential and that the later could not be substituted by either cell-free bacterial culture supernatant, or bacterial cell lysate. Further, we found that the gut pH profile and presence of proteolytic activity could be observed in larvae colonized only with select members of the microbiota that are capable of secreting extracellular protease. Collectively, our findings suggest a novel and interesting evolutionary mechanism of host-microbe interaction, in which select members of the gut microbiota promote larval nutrition, growth and development by providing protease and creating ionic microenvironment optimal for its activity.