Study On Activity Of Antimicrobial Peptide Hidefensin1-1 From Hermetia Illucens And Effect Of Its Worm Meal On The Growth Of Grass Carp

Black soldier fly,Hermetia illucens,always grow in the environment with large number of pathogenic microorganisms.They were fed on food waste and livestock manure without being infected by pathogenic microorganisms,that thanks to the presence of various natural antimicrobial peptides in the black soldier fly.Antimicrobial peptides are small peptides with antibacterial activity,which are not easily lead pathogenic microorganisms to be antibiotic resistance,due to their special antibacterial mechanism.In recent years,the various problems caused by the misuse of antibiotics in livestock and aquaculture industries.That has made antimicrobial peptides to be the primary alternative to antibiotics.The research work in this thesis is based on the genome annotation of black soldier fly Wuhan strain to predict the three-dimensional structure and function of six defensin family antimicrobial peptides.The amino acid sequences of these six antimicrobial peptides all contain six conserved cysteine residues that can form three stable disulfide bonds to maintain their spatial structures.It was predicted that the β-fold structure contained in the molecular structure of the antimicrobial peptide Hidefensins plays a key important role in its antimicrobial activity.And the C-terminus of its amino acid sequence contains multiple clusters of cationic residues such as arginine and lysine,which can make these peptides more easily attracted and adhered to the negatively charged bacterial surface,resulting in higher antimicrobial activity and targeting.In this study,the antimicrobial peptide Hidefensin1-1 was used as a representative of the defensin family of antimicrobial peptides to verify the antibacterial activity in vitro.The fusion antimicrobial peptide TRX-Hidefensin1-1 was expressed and purified in E.coli BL21(DE3),and the fusion protein TRX-Hidefensin1-1 with a concentration of 0.132 mg/m L was obtained.The results showed that TRX-Hidefensin1-1 exhibited good inhibition activity against both Gram-positive(Staphylococcus aureus)and Gram-negative(Escherichia coli)pathogens in vitro.This experiment provides a theoretical basis for the large-scale production of defensin family antimicrobial peptides and their application in biological feed additives.Black soldier fly larvae contain a variety of nutrients necessary for animal growth such as protein,fatty acids and substances with antibacterial activity,which are used in livestock breeding and aquaculture with various forms.Grass carp is the most widely farmed freshwater fish in China,and the rising price of feed ingredients and the occurrence of diseases during the farming process are great challenges in the grass carp farming industry.In this study,we investigated the effect of black soldier fly larvae meal(BSFLM)on the growth and intestinal health of grass carp by using BSFLM as feed additives in grass carp culture.It was found that the addition of black soldier fly larvae meal could significantly improve the condition factor of grass carp.When 4% of BSFLM was added,it could significantly improve the weight gain rate and specific growth rate of grass carp.2% and 4% of BSFLM could significantly reduce the feed coefficient rate.Meanwhile,the addition of 1% and 2% of BSFLM could increase the length of villi and depth of crypt in the intestine of grass carp,which significantly improved their intestinal environment.The results of this study showed that BSFLM could enhance the growth performance and improve the intestinal health of grass carp,providing a basis for the role of BSFLM as a feed additive to reduce feed costs and prevent intestinal diseases in grass carp culture.