Broad-spectrum antimicrobial activity in vitro of the synthetic peptide D4E1

Broad-spectrum antimicrobial activity of a synthetic peptide, D4E1, is docu mented in this paper. D4E1 inhibited the growth of several fungal phytopath ogens belonging to four classes-Ascomycetes, Basidiomycetes, Deuteromycetes , and Oomycetes, and two bacterial pathogens, Pseudomonas syringae pv. taba ci and Xanthomonas campestris pv. malvacearum race 18. The minimum inhibito ry concentration (MIC) of D4E1 required to completely inhibit the growth of all fungi studied ranged from 4.67 to 25 muM. Fungal pathogens highly sens itive to D4E1 include Thielaviopsis basicola, Verticillium dahliae, Fusariu m moniliforme, Phytophthora cinnamomi, and Phytophthora parasitica. Compara tively, the least sensitive fungal pathogens were Alternaria alternata, col letotrichum destructivum, and Rhizoctonia solani. The two bacterial pathoge ns, P. syringae pv. tabaci and X. campestris pv. malvacearum race 18, were most sensitive to D4E1 with MIC values of 2.25 and 1.25 muM, respectively. Microscopic analysis of D4E1 effects on fungal morphology of Aspergillus fl avus and R. solani revealed abnormal hyphal growth and discontinuous cytopl asm. After 8 h of exposure to 25 muM D4E1, A. flavus spore germination was reduced by 75%. The suitability of peptide D4E1 to enhance disease resistan ce in transgenic crop plants is discussed.