Acetoin production, by beneficial rhizobacteria, plays an important role in plant growth and resistance to plant pathogens. The aim of this work was to optimize the nutritional conditions using statistically based experimental designs for the production of B. subtilis GB03 acetoin.

Eight components of the medium and cultivation conditions were examined for their significance on the production of acetoin using the Plackett–Burman experimental design. Steepest ascent experiments were employed to approach the optimal region of the three factors and a central composite design was applied to determine their optimal levels.

Results indicated that glucose, ammonium phosphate and agitation speed had significant effects on the acetoin production. The significant medium components in our optimization medium were 75.91 g/l of glucose, 5.79 g/l of ammonium phosphate, and 213rpm of agitation speed. The maximum acetoin concentration of 26.1 g/l at 40 h was obtained. Volatiles emitted from bacteria on optimized medium showed phytotoxicity on Arabidopsis seedlings. Result revealed that 1 ppm of acetoin was the best for the promotion of plant growth. Discussion and

Statistical experimental designs appeared to be an influential tool for optimization of fermentation conditions to enhance the acetoin production. However, volatile components secreted from the bacteria in the optimized medium showed some degree of phytotoxicity on Arabidopsis seedlings.