Characterization of antimicrobial metabolites produced by the bacterium Pseudomonas fluorescens X

Pseudomonas fluorescens X is an efficient biological antagonist of soil borne phytopathogenic fungi that cause damping-off of seeds and seedlings. In order to investigate the mechanism of its biological activity, mutants deficient in the antifungal activity in vitro and in vivo were generated by mutagenesis using the transposon Tn5. Fun-gitoxicity tests of bacterial extracts from solid cultures of the wild type and mutant strains showed significant reduction of mycelia growth of Pythium ultimum only in the case of the wild type. These results indicate that the possible mechanism of biological activity of P. fluorescens is due to the production of antimicrobial metabolites. A method using semi-preparative high performance liquid chromatography (HPLC), was developed for the isolation of these substances. In vitro bioassays were followed to test the isolated compounds for antifungal activity. Direct application of each of these purified metabolites with Pythium ultimum, resulted in growth suppression of fungi. Structure elucidation using atmospheric pressure chemical ionization-mass spectrometric detector (APCI-MSD) suggested that they are probably antibiotics due to their low molecular weight. Chemical structure is currently being analyzed by FT-IR.