Bacteriocin production by Pseudomonas syringae pv. ciccaronei NCPPB2355. Isolation and partial characterization of the antimicrobial compound

Pseudomonas syringae pv. ciccaronei strain NCPPB2355 was found to produce a bacteriocin inhibitory against strains of Ps. syringae subsp. savastanoi, the causal agent of olive knot disease. Treatments with mitomycin C did not substantially increase the bacteriocin titre in culture. The purification of the bacteriocin obtained by ammonium sulphate precipitation of culture s upernatant fluid, membrane ultrafiltration, gel filtration and preparative PAGE, led to the isolation of a high molecular weight proteinaceous substan ce. The bacteriocin analysed by SDS-PAGE revealed three protein bands with molecular weights of '76, 63 and 45 kDa, respectively. The bacteriocin was sensitive to heat and proteolytic enzymes, nias resistant to non-polar orga nic solvents and was active between pH 5.0-7.0. Plasmid-DNA analysis of Ps. syringae ciccaronei revealed the presence of 18 plasmids; bacteriocin-nega tive variants could not be obtained by cure experiments.