Improvement of the Efficacy of Linear Undecapeptides against Plant-Pathogenic Bacteria by Incorporation of d-Amino Acids

Abstract

ABSTRACTA set of 31 undecapeptides, incorporating 1 to 11d-amino acids and derived from the antimicrobial peptide BP100 (KKLFKKILKYL-NH2), was designed and synthesized. This set was evaluated for inhibition of growth of the plant-pathogenic bacteriaErwinia amylovora,Pseudomonas syringaepv. syringae, andXanthomonas axonopodispv. vesicatoria, hemolysis, and protease degradation. Two derivatives were as active as BP100, and 10 peptides displayed improved activity, with the all-disomer being the most active. Twenty-six peptides were less hemolytic than BP100, and all peptides were more stable against protease degradation. Plant extracts inhibited the activity of BP100 as well as that of thed-isomers. Ten derivatives incorporating oned-amino acid each were tested in an infectivity inhibition assay with the three plant-pathogenic bacteria by using detached pear and pepper leaves and pear fruits. All 10 peptides studied were active againstE. amylovora, 6 displayed activity againstP. syringaepv. syringae, and 2 displayed activity againstX. axonopodispv. vesicatoria. Peptides BP143 (KKLFKKILKYL-NH2) and BP145 (KKLFKKILKYL-NH2), containing oned-amino acid at positions 4 and 2 (underlined), respectively, were evaluated in whole-plant assays for the control of bacterial blight of pepper and pear and fire blight of pear. Peptide BP143 was as effective as streptomycin in the three pathosystems, was more effective than BP100 against bacterial blight of pepper and pear, and equally effective against fire blight of pear.