Effects of Microorganisms on Growth Performance, Body Composition, Digestive Enzyme Activity, Intestinal Bacteria Flora and Antimicrobial Peptide (AMP) Content of Black Soldier Fly Larvae (Hermetia illucens)

Antimicrobial peptides (AMPs) are a class of small-molecule active polypeptides. Because of their good antibacterial activity, stability and safety, AMPs are considered one of the potential alternatives to antibiotics. Black soldier fly (Hermetia illucens) is an excellent material for the study of AMPs. This study aims to screen optimum microbial strains and concentration to support the growth performance and AMP induction of H. illucens. Six microorganisms were selected as feed additives for H. illucens by tracking the growth performance, proximate composition, digestive ability and AMP content in the first trial. Microorganism efficiency screening results showed that Rhodopseudomonas palustris (RP) could improve growth performance, digestive ability and AMP content of H. illucens. Therefore, RP was selected to prepare the diets and was incorporated into diets for H. illucens at different levels. The results showed that RP is superior to the other strains as a feed additive for the H. illucens larvae, and we recommend the addition of 1.22 x 10(9)-1.22 x 10(10) CFU/g RP to promote the growth and AMP content of H. illucens. This study provides new ideas for largescale production of AMPs and lays the foundation for the development of AMPs as feed additives to substitute antibiotics.Abstract: Escherichia coli (EC), Staphylococcus aureus (SA), Bacillus subtilis (BS), Rhodopseudomonas palustris (RP), Saccharomyces cerevisiae (SC) and Lactobacillus plantarum (LP) were selected as feed additives for black soldier fly (Hermetia illucens) by tracking the growth performance, proximate composition, digestive ability and antibacterial peptides (AMPs) content in the first trial. Microorganism efficiency screening results showed that RP could improve growth performance, digestive ability and AMP content of H. illucens. Therefore, RP was selected to prepare the diets and was incorporated into diets for H. illucens at levels of 0 (R0), 1.22 x 10(6) (R1), 1.22 x 10(7) (R2), 1.22 x 10(8) (R3), 1.22 x 10(9) (R4) and 1.22 x 10(10) (R5) CFU/g. After 5 d of feeding, larvae fed the R2-R5 diets had higher weight gain and specific growth rates. Different concentrations of RP had no significant effect on larval body composition. R4-R5 could improve the digestibility and expression of AMPs in larvae. Moreover, RP could significantly increase the abundance of Lactobacillus and Rhodopseudomonas and decrease the abundance of Proteus and Corynebacterium. Therefore, RP is superior to the other strains as a feed additive for H. illucens larvae, and we recommend the addition of 1.22 x 10(9)-1.22 x 10(10) CFU/g RP to promote the growth and AMP content of H. illucens.