Financial support: Grant 1951105 from Fondecyt.

Keywords: Bacillus subtilis, biological control, iturin.

Present address: ^#Programa de Biología Celular y Molecular, ICBM, Facultad de Medicina, Universidad de Chile, Independencia 1027, Santiago, Chile. Casilla 70086. Tel: 56 02 6786207. Fax: 56 02 7355580.

The use of microorganisms for biological purposes has become an effective alternative to control plant pathogens. There are many examples of formulations using bacterial or fungal strains with biocontrol applications. Among them, members of the genus Bacillus are well known antibiotic producers. However, the increased capacity of antibiotic production obtained by direct mutagenesis of wild strains, has seldom been reported in the open literature. This research refers to the mutation of the A47 Bacillus strain, a plant pathogen antagonist, in order to obtain an improved strain with enhanced capacity to synthesize metabolites with antibiotic activity. The mutant strain M40 was obtained using the mutagenic agent acridine orange. The mutant strain showed a higher antagonistic activity than the wild type A47 against the plant pathogen Botritys cinerea (grey mould), Ralstonia solanacearum (bacterial wilt) and Erwinia carotovora var. carotovora (bacterial soft rot). The final objective was to isolate the antibiotic metabolite produced by the M40 strain and to determine its chemical and antibiotic properties. The results revealed the presence of an extracellular, thermostable and methanol-soluble metabolite that absorbed light at 212nm. These characteristics are similar to those described for cyclic antibiotic lipopeptides such as iturins.