Intestinal commensal bacteria promote Bactrocera dorsalis larval development through vitamin B6 synthesis pathway

Background The gut microbiota can facilitate host growth under nutrient-constrained conditions. However, whether this effect is limited to certain bacterial species remains largely unclear, and the relevant mechanisms remain to be thoroughly investigated. Results Here, we found that the microbiota was required for Bactrocera dorsalis larval growth under poor diet conditions. Mono-association experiments revealed that Enterobacteriaceae and some Lactobacilli promoted larval growth. Of 27 tested bacterial strains, 15 strains significantly promoted larval development, and the Enterobacteriaceae cloacae N29 isolate exhibited the most obvious promoting effect. Bacterial genome-wide association study (GWAS) revealed that the vitamin B6 synthesis pathway was critical for E. cloacae growth promotion. The deletion of pdxA responsible for the vitamin B6 biosynthesis deprived the mutant strains of larval growth promotion function, indicating that pdxA gene was crucial for promoting larval growth in the N29 strain. Importantly, supplementation of vitamin B6 to poor diet successfully rescued the axenic larval growth phenotype of B. dorsalis . Conclusion Our results suggest that gut microbes promote insect larval growth by providing vitamin B6 under nutrient scarcity in B. dorsalis . ### Competing Interest Statement The authors have declared no competing interest.