Compartmentalized immune expression along the Hermetia illucens midgut forms characteristic gut microbiota
The immune system in the black soldier fly larva(Hermetia illucens L.,BSFL)gut must eliminate pathogens while tolerating the presence of symbiotic microbiota.The Tol and Imd pathway is an essential defense against invading pathogens in insect guts,but tolerance mechanisms are less understood.This study compared the BSFL midgut microbiota in different types of waste(food waste,bean dregs,and chicken manure)and found that Actinobacteria,Firmicutes,Bacteroidetes,and Proteobacteria were dominant in the midgut,and midgut could enrich Actinobacteria and Bacteroidetes.According to the random forest model prediction,the Dysgonomonas,Morganella,and Anaerococcus were most likely to be the characteristic genus in the midgut.Further research had shown that the microbial load in the posterior midgut was 4.52～12.6 times higher than that in the anterior and middle midgut,and that Pseudomonas aeruginosa was mainly enriched in the posterior midgut.In addition,the expression of antimicrobial peptides in the anterior and middle midgut was 1 645 times and 10.2 times higher than that in the posterior midgut,respectively,while the expression of negative feedback factors increased by 4.28～5.04 times in the posterior midgut.This study demonstrated that BSFL midgut had a reconstruction effect on microorganisms.The larvae screen microorganisms through antimicrobial peptides in the anterior midgut and inhibit the release of antimicrobial peptides in the posterior midgut to preserve symbiotic bacteria.Our study describes a'elimination-then-recruitment'mechanism by which regional expression of immune system in midgut maintains their ability to resist pathogens while constructing protective zones for the symbiotic microbiota.
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