An analysis of a series of five peptides composed of various portions of the pleurocidin (Plc) sequence identified a l2-amino acid fragment from the C-terminus of Plc, designated Plc-2, as the smallest fragment that retained a antimicrobial activity comparable to that of the parent compound. MIC tests in vitro with low-ionic-strength medium showed that Plc-2 has potent activity against Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus but not against Enterococcus faecalis. The antifungal activity of the synthetic peptides against phytopathogenic fungi, such as Fusarium oxysporum, Colletotrichum sp., Aspergillus niger and Alternaria sp., also identified Plc-2 as a biologically active peptide. Microscopy studies of fluorescently stained fungi treated with Plc-2 demonstrated that cytoplasmic and nuclear membranes were compromised in all strains of phytopathogenic fungi tested. Together, these results identify Plc-2 as a potential antimicrobial agent with similar properties to its parent compound, pleurocidin. In addition, it demonstrated that the KHVGKAALTHYL residues are critical for the antimicrobial activity described for pleurocidin.

The search for environmentally biocompatible and cost-effective methods to control filamentous fungi in agriculture is becoming increasingly urgent. In vitro antimicrobial activity of three synthetic peptides was investigated against some filamentous fungi with agricultural relevance. The peptides were an analog of Temporin called Temporizina, a fragment from Pleurocidin termed Plc-2, and a peptide identified from sesame seeds named Pses3. Antimicrobial activity of these peptides towards filamentous fungi has not been previously reported. Seven plant pathogenic or mycotoxigenic fungal species, isolated from plant tissues were assayed: Alternaria solani, Colletotrichum gloesporioides, Fulvia fulvum, Fusarium oxisporum, Aspergillus niger, A. ochraceus and Penicillium digitatum. Values of Minimum Inhibitory Concentration (MIC) and Minimum Fungicidal Concentration (MFC) were determined and compared with the commercially available fungicide Captan as a positive control. The peptides showing greatest inhibition were Pses3 and Plc-2 and C. gloesporioides was the most sensitive of the evaluated fungi. The MIC values for Plc-2 and Pses3 peptides ranged from 0.64 µM to 10.25 µM. These values were much lower than those observed for Captan, suggesting the potential of these peptides as fungicides. In particular, Pses3 is a novel peptide derived from sesame seeds not reported in databases.