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Abstract
A 125-member library of synthetic linear undecapeptides was prepared based on a previously
described peptide H-K(1)KLFKKILKF(10)L-NH(2) (BP76) that inhibited in vitro growth
of the plant pathogenic bacteria Erwinia amylovora, Xanthomonas axonopodis pv. vesicatoria,
and Pseudomonas syringae pv. syringae at low micromolar concentrations. Peptides were
designed using a combinatorial chemistry approach by incorporating amino acids possessing
various degrees of hydrophobicity and hydrophilicity at positions 1 and 10 and by
varying the N-terminus. Library screening for in vitro growth inhibition identified
27, 40 and 113 sequences with MIC values below 7.5 microM against E. amylovora, P.
syringae and X. axonopodis, respectively. Cytotoxicity, bactericidal activity and
stability towards protease degradation of the most active peptides were also determined.
Seven peptides with a good balance between antibacterial and hemolytic activities
were identified. Several analogues displayed a bactericidal effect and low susceptibility
to protease degradation. The most promising peptides were tested in vivo by evaluating
their preventive effect of inhibition of E. amylovora infection in detached apple
and pear flowers. The peptide H-KKLFKKILKYL-NH(2) (BP100) showed efficacies in flowers
of 63-76% at 100 microM, being more potent than BP76 and only less effective than
streptomycin, currently used for fire blight control.