Inhibition of plant-pathogenic bacteria by short synthetic cecropin A-melittin hybrid peptides

Abstract

Short peptides of 11 residues were synthesized and tested against the economically important plant pathogenic bacteria Erwinia amylovora, Pseudomonas syringae, and Xanthomonas vesicatoria and compared to the previously described peptide Pep3 (WKLFKKILKVL-NH(2)). The antimicrobial activity of Pep3 and 22 analogues was evaluated in terms of the MIC and the 50% effective dose (ED(50)) for growth. Peptide cytotoxicity against human red blood cells and peptide stability toward protease degradation were also determined. Pep3 and several analogues inhibited growth of the three pathogens and had a bactericidal effect at low micromolar concentrations (ED(50) of 1.3 to 7.3 microM). One of the analogues consisting of a replacement of both Trp and Val with Lys and Phe, respectively, resulted in a peptide with improved bactericidal activity and minimized cytotoxicity and susceptibility to protease degradation compared to Pep3. The best analogues can be considered as potential lead compounds for the development of new antimicrobial agents for use in plant protection either as components of pesticides or expressed in transgenic plants.

FIG. 1.

Edmunson wheel projection of the 11-mer peptides that were synthesized. Black background, hydrophilic amino acids (Lys); white background, hydrophobic amino acids; gray background, residues that can be either hydrophilic (Lys) or hydrophobic (Leu, Trp, Tyr, and Phe), depending on the sequence as shown in Table 1.

FIG. 2.

Kinetics of survival of P. syringae, X. vesicatoria, and E. amylovora in the presence of Pep3 (○) or selected analogues. Bacterial suspensions were untreated (▪) or treated with 5 μM concentrations of BP11 (▵), BP15 (⋄), BP33 (⧫), or BP76 (•), and viable cells were determined at different time intervals.

FIG. 3.

Kinetics of digestion of Pep3 (○) and selected analogues BP08 (—), BP20 (✻), BP33 (⧫), and BP76 (•) by proteinase K.