Production of syringotoxin and other bioactive peptides by Pseudomonas fuscovaginae

The application of a cell-free extract from a broth culture of Pseudomonas fuscovaginae to rice plants produced leaf sheath necrosis and inhibited panicle emergence typical of bacterial sheath rot. The extract was also fungistatic to Geotrichum candidum and displayed amphipathic properties. The toxic activity was associated with peptidic substances of less than 5000 Da, migrating in a single broad band on SDS-PAGE. The toxins were precipitated by desoxycholate/trichloroacetic acid and reverse-phase HPLC of the precipitate showed the presence of five peptidic compounds (A, B, C, D and E), as well as two others (fuscopeptins A and B) which were nor characterized in this study. Using FAB-MS, the MH(+) ions of the peptides: A to E were 1108, 1102, 1118, 1136 and 1152, respectively. The most abundant peptide, D, was characterized by amino acid analysis, fatty acid methyl ester analysis and FAB-MS of the by-products from mild alkaline hydrolysis. The chemical structure of D was identical to syringotoxin (C48H82O18N11Cl), a phytotoxin produced by P. syringae pv. syringae Moreover, HPLC analysis of this compound indicated that compound D had the same retention time as the syringotoxin standard obtained from citrus strains of P. syringae pv. syringae. (C) 1996 Academic Press Limited.