Enhanced iturin A production by Bacillus subtilis and its effect on suppression of the plant pathogen Rhizoctonia solani.

Enhanced production of the antibiotic iturin A by Bacillus subtilis RB14-CS reached 4.4 g L(-1) in SM medium containing soybean meal and maltose, which was 16-fold and 2.2-fold higher than that in original and modified number 3S media, respectively. When various volumes of RB14-CS cultures grown in SM medium were applied to pot tests of tomato damping-off caused by Rhizoctonia solani, damping-off was dose-dependently suppressed by the cultures. Suppression by SM-grown cultures was significantly more effective than that by cultures grown in original or modified number 3S media. The iturin A concentrations in soil decreased to undetectable levels after 17 days of cultivation in pot tests, indicating that iturin A has a low persistence in soil.