The Dissection On The Mechanism Of Gut Bacteria Enhancing The Systemic Immunocompetence Of Drosophila Melanogaster

The gut of Drosophila melanogaster is often colonized by 5-20bacterial species,Acetobacter pomorum and Lactobacillus plantarum are the dominant ones.Previous studies have demonstrated that gut microbiota can shape the immune systme of host animals.However,the physiological mechanisms by which gut bacteria improve the immunocompetence of host animals remain mostly unknown.The mechanisms of gut bacteria enhancing the systemic immunocompetence of D.melanogaster adults were dissected by constructing germfree and gnotobiotic insects,analyzing survival percentage after the challenge of its pathogenic bacterium Staphylococcus aureus and determining the expression level of some immunity-related genes by RT-q PCR.Our results indicated that the removal of gut bacteria can significantly decreased the survival rate of D.melanogaster adults after the exposure of the pathogenic bacterium S.aureus.Furthermore,the bacterial clearance ability of D.melanogaster and the expression level of antimicrobial peptide（AMP）genes,Diptericin and Defensin,in the fat body were impaired dramatically,suggesting that gut bacteria can improve the systemic immunocompetence of D.melanogaster adults by enhancing the expression level of AMP genes in fat body.The colonization of A.pomorum significantly increased the systemic immunocompetence of germfree adults,indicating that A.pomorum is the vital bacterial species to shape the immunity of D.melanogaster adults.Furthermore,the feeding of an A.pomorum-derived metabolite,acetic acid,significantly improved the systemic immunocompetence of germfree flies,implying that this metabolite is the important gut bacteria-derived signal to impact the immune system of D.melanogaster adults.Finally,nonsignificance was determined in the systemic immunocompetence between the conventionally reared PGRP-LC^-/-and wild type adults,suggesting PGRP-LC is a vital receptor to mediate the effect of gut bacteria on the systemic immunocompetenc of D.melanogaster.In conclusion,this study confirmed that gut bacteria can significantly improve the systemic immunocompetence of D.melanogaster via PGRP-LC-dependent manner,and A.pomorum-derived acetic acid is an important signal.However,the mechanism of acetate and PGRP-LC mediating the regulation of gut microbiota on the systemic immunocompetence of D.melanogaster needs further investigation.