Facultative secondary symbiont drives the physiological and metabolic alterations of insect host

Lepidoptera comprise the second most diverse insect order in worldwide, including some of the most devastating agricultural pests and important economic insects. Silkworm is an ideal model for studying the symbiosis between bacteria and insects. Bacterial secondary symbionts in the gut are widespread in insects. Symbionts often enhance host ability to acquire nutrients from the environment or provide the pathways for synthesis of needed organic compounds or for catabolism of molecules available in the environment. B. subtilis is one of the main components of symbiotic bacteria in the digestive tract of silkworm. Previous studies have indicated that B. subtilis can promote the growth and development and maintain health of silkworm. However, to date, the ecological role of these Bacillus relatives to the Lepidoptera remains obscure. Therefore, in this study, we employed the B. subtilis isolated from silkworm intestine to explore the mode of action of Bacillus on Lepidoptera.