Antimicrobial Activity of Secondary Metabolites Produced by Different Pathovars of <em>PSeudomonas syringae</em> and by Strains of <em>P. avellanae</em>

Abstract

Several species in the genus Pseudomonas produce secondary metabolites showing phytotoxic and antimicrobial activity. Thirty-three strains of nine pathovars of P. syringae and four strains of P. avellanae were tested for antibacterial and antifungal activity using Bacillus megaterium and Rhodotorula pilimanae as assay organisms. The assay was carried out on nine different media. Inhibitory behaviour was found with almost all the media tested. Medium 523 favoured the production of antimicrobial substances against B. megaterium. Medium King B was the optimal substrate, allowing 95% of the strains to inhibit R. pilimanae growth. Medium IMMA appeared the best substrate for inducing lipodepsipeptide production. Dendrograms drawn on the basis of the activity of each pathovar or species vs B. megaterium or R. pilimanae gave a representation of non-homogenous clusters. A dendrogram combining pathovar data from tests against both B. megaterium and R. pilimanae gave homogenous clusters which showed a similarity between the pathovars. The strains of pv. aptata, lachrymans and syringae were lipodepsinonapeptide and syringopeptin producers. The toxigenic activity of these bacteria may improve the diagnosis and identification of P. syringae pathovars.