PRODUCTION OF SYRINGOMYCINS AND SYRINGOPEPTINS BY PSEUDOMONAS-SYRINGAE PV ATROFACIENS

All virulent strains of Pseudomonas syringae pv. atrofaciens produce i n vitro substances with syringomycin-like features. All strains inhibi ted the growth of Geotrichum candidum in the plate assay although the extent of their growth inhibition was variable. Purification of bioact ive culture extracts of a highly virulent strain by ion exchange chrom atography (Whatman CM52) yielded a main fraction which inhibited the g rowth of Rhodotorula pilimanae and Bacillus megaterium, and was phytot oxic to tobacco and wheat plants. In particular, the injection of this fraction in the culm of wheat plants caused phytotoxic symptoms on le aves similar to those caused in nature by the pathogen. The further pu rification by HPLC of the above fraction gave rise to four main bioact ive substances which have been identified by spectroscopic methods (FA B-MS) and amino acid analysis as syringomycin E, syringomycin G, syrin gopeptin 25A and syringopeptin 25B, toxic lipodepsipeptides thus far r ecognized to be produced by most strains of P. syringae pv. syringae. The injection of both syringomycin E and syringopeptin 25A in wheat le aves caused necrotic symptoms; however, syringopeptin 25A was at least six times more active than syringomycin E. The possible role of the t oxins in the disease development on cereals and the need for a careful examination of pathogenetic and biochemical features of P. syringae p v. atrofaciens to establish the relationships of the two pathovars in the 'syringae group' are discussed.