Abstract
BackgroundThe importance of poultry as a global source of protein underpins the chicken genome and associated SNP data as key tools in selecting and breeding healthy robust birds with improved disease resistance. SNPs affecting host peptides involved in the innate defences tend to be rare, but three non-synonymous SNPs in the avian β-defensin (AvBD1) gene encoding the variant peptides NYH, SSY and NYY were identified that segregated specifically to three lines of commercial broiler chickens Line X (LX), Line Y(LY) and Line Z. The impacts of such amino acid changes on peptide antimicrobial properties were analysed in vitro and described in relation to the caecal microbiota and gut health of LX and LY birds.ResultsTime-kill and radial immune diffusion assays indicated all three peptides to have antimicrobial properties against gram negative and positive bacteria with a hierarchy of NYH > SSY > NYY. Calcein leakage assays supported AvBD1 NYH as the most potent membrane permeabilising agent although no significant differences in secondary structure were identified to explain this. However, distinct claw regions, identified by 3D modelling and proposed to play a key role in microbial membrane attachment, and permeation, were more distinct in the NYH model. In vivo AvBD1 synthesis was detected in the bird gut epithelia. Analyses of the caecal gut microbiota of young day 4 birds suggested trends in Lactobacilli sp. colonisation at days 4 (9% LX vs × 30% LY) and 28 (20% LX vs 12% LY) respectively, but these were not statistically significant (P > 0.05).ConclusionAmino acid changes altering the killing capacity of the AvBD1 peptide were associated with two different bird lines, but such changes did not impact significantly on caecal gut microbiota.
Highlights
The importance of poultry as a global source of protein underpins the chicken genome and associated Single nucleotide polymorphism (SNP) data as key tools in selecting and breeding healthy robust birds with improved disease resistance
Blood agar was used for the growth of E. coli and E. faecalis; brain heart infusion (BHI) broth and agar were used for the growth of B. viscericola
Examination of the Avian β-defensin (AvBD) locus on chromosome 3 identified 15 SNPs that were exhibited by three bird lines Line X (LX), Line Y (LY) and Line Z (LZ) shown by linkage disequilibrium to be phylogenetically distinct [19]
Summary
The importance of poultry as a global source of protein underpins the chicken genome and associated SNP data as key tools in selecting and breeding healthy robust birds with improved disease resistance. SNPs affecting host peptides involved in the innate defences tend to be rare, but three non-synonymous SNPs in the avian β-defensin (AvBD1) gene encoding the variant peptides NYH, SSY and NYY were identified that segregated to three lines of commercial broiler chickens Line X (LX), Line Y(LY) and Line Z The impacts of such amino acid changes on peptide antimicrobial properties were analysed in vitro and described in relation to the caecal microbiota and gut health of LX and LY birds. The defensins comprise groups of innate effectors synthesised by epithelia and antigen presenting cells that function as a first line defence mechanism to protect the host from infection These small molecular weight molecules, less than 50 aa in length and 2 to 6 kDa in size, are noted for their broad-spectrum anti-microbial properties, which are facilitated through their small size, cationic charge and preponderance of hydrophobic amino acids [1, 2]. These observations suggest that interactions between genetic and environmental factors are important, but multifaceted, and for breeding purposes direct the selection of SNPs less sensitive to environmental changes [10]
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