Bacteriocin production by Pseudomonas syringae subsp. savastanoi.
Representative strains of P. s. pv. savastanoi from each of the 6 host species (olive, oleander (Nerium oleander), ash tree (Fraxinus), privet (Ligustrum spp.), jasmine, Phillyrea sp.) were assayed for bacteriocin production. Of 78 strains, 39 (50%) produced bacteriocins on nutrient-yeast extract agar (NYA). Production in liquid medium (NYB) was poor and was not induced by treatment with mitomycin C or UV irradiation. The majority (75%) of the 31 olive and all the Fraxinus (13) and jasmine (3) strains assayed produced bacteriocins. In contrast, N. oleander, Ligustrum and Phillyrea strains did not produce bacteriocins. Based on these results, bacteriocinogenicity was related to the host origin of the strains. It is concluded that bacteriocins produced by P. s. pv. savastanoi (savastanoicins) are substances of high MW, sensitive to heat (20 min at 80°C) and proteolytic enzymes. They inhibited the growth of strains belonging to the same subspecies and did not inhibit strains of the related pathovars, including syringae, glycinea and phaseolicola. The relationship between bacteriocinogenicity and survival of the pathogen on the host phylloplane is discussed.