FIGURE 1.

The effect of 2,3-butanediol produced by Bacillus subtilis on bacterial rhizosphere competence. Pepper roots were inoculated with 5 ml of bacterial suspension at 10⁸ cfu/ml (day 0). Pepper root samples were collected after removal of soil from roots. (A) Population densities of B. subtilis strains 168, 2,3-B(++), and 2,3-B(-) isolated from pepper roots 0, 7, 14, 21, and 28 days after inoculation. B. subtilis 168, the wild type; 2,3-B(++), 2,3-butanediol overexpression mutant derived from B. subtilis 168; 2,3-B(-), 2,3-butanediol null mutant derived from B. subtilis 168. (B) Fungal colonies on tryptic soy agar containing 100 μg/ml rifampicin recovered from pepper roots inoculated with strains 168, 2,3-B(++), and 2,3-B(-). (C) Direct inhibition test of 2,3-butanediol. 50 μl undiluted solution 1 (1), 10 fold diluted (2), and 100 fold diluted solution (3) 2,3-butanediol was spot-inoculated on the paper disks following spreading 10⁵ cfu/ml Trichoderma sp., spores. The 50 μl water treatment was used as control (4).