Isolation and Characterization of Antifungal Secondary Metabolites Produced by Rhizobacteria from Common Bean

Conventional management of crops implies excessive use of fungicides. Rhizobacteria with antagonistic effects against phytopathogens constitute an alternative to chemical control. The aim of this work was to isolate and characterize secondary metabolites with antifungal activity produced by rhizobacteria. Several bacterial strains isolated from the rhizosphere of common bean plants were evaluated for their ability to suppress the growth of fungal phytopathogens due to the production of volatile and non-volatile compounds. Among them, Bacillus sp. B02 was selected as an antagonistic microorganism with capacity to produce non-volatile metabolites. Antifungal compounds were produced at 72 h in mineral broth supplemented with starch (20 g l(-1)) and yeast extract (5 g l(-1)). The metabolites were isolated from cell free supernatants by precipitation after they were acidified to pH 2 and characterized by their polarity and by thin layer chromatography (TLC) analysis. Lipophilic compounds were extracted using a chloroform:methanol (2:1, v/v) system. In addition, polar antifungal compounds were presented in butanol, acetone and methanol crude extracts. The extracts inhibited the mycelial growth of R. solani. TLC revealed the presence of lipid compounds when iodine vapor was used as reagent. This result showed the amphiphilic character of the antifungal compounds produced by Bacillus sp. B02 which probably correspond to lipopeptides.