The nutritional requirements for antimicrobial activity of Streptomyces rimosus AG-P1441 were optimized using statistically-based experimental designs at a flask level. Based on a one-factor-at-a-time (OFAT) approach, glucose, corn starch and soybean meal were identified as the carbon and nitrogen sources having a significant effect on antimicrobial productivity. As a result of investigating the effect of glucose concentration, the highest antimicrobial activity was observed at 3% concentration. Response surface methodology (RSM) was then applied to optimize the growth medium components (corn starch, soybean meal, MgCl2 and glutamate). Antimicrobial productivity increased sharply when the medium consisted of 3% glucose, 3.5% corn starch, 2.5% soybean meal, 1.2 mM MgCl2 and 5.9 mM glutamate. The fermentation using optimized culture medium in a 5-L bioreactor allowed a significant increase in antimicrobial activity, evaluated by the paper disc assay, revealed a 29 mm inhibition zone diameter against Phytophthora capsici.
Keywords: Biocontrol; Medium optimization; Phytophthora capsici; Streptomyces rimosus AG-P1441.