P86: High throughput screening method for Bacillus sp. mutants with reduced antibacterial inhibitory effect

Some Gram positive Bacillus sp. secrete antibacterial compounds that are inhibitory to other Gram positive bacteria. After generating mutants of Bacillus sp by UV-exposure, a high throughput screening method was applied for selection of Bacillus sp. mutants with reduced antibacterial inhibitory effect. A Lactococcus lactis subsp. cremoris indicator strain was susceptible to inhibition by the Bacillus sp. mother strain. The indicator strain was cultivated in brain heart infusion broth supplemented with Bacillus sp. spent media and growth was monitored by continuous optical density measurements for 18 hours. Out of more than 9000 Bacillus mutants screened, several leads were tested by plate well diffusion assay, and 5 were confirmed to have reduced inhibitory effect on the indicator strain. An inhibitory compound secreted by the mother strain was reduced to 3-46% in selected mutants, as determined by HPLC analysis. The HTS method may be used as a general screening method for mutants with reduced inhibitory effect on indicator bacteria.