The influences of culture media, temperature, and light/dark conditions on growth and antifungal activity of the three strains Streptomyces spp. against Botrytis cinerea was studied. Results of in vitro study indicated that the GYM agar and incubated at 28°C exhibited good mycelial growth and a spore mass production of the three strains of Streptomyces spp. On the other hand, the PDA and incubation at 21°C were suitable for the mycelial growth of B. cinerea . Moreover, light/dark conditions had an effect on the growth of the two strains of S. philanthi . The strains RL-1-178 and RM-1-138 of S. philanthi grown in all media and incubation temperatures tested possessed antifungal activity against B. cinerea (100% inhibition) while S. mycarofaciens showed different results on PDA (83% inhibition) and GYM (88% inhibition) with the optimum incubation temperature at 21°C. Then, the antifungal compounds in culture filtrates produced by the three antagonistic strains against B. cinerea were tested on tomato leaf. They showed a significantly higher inhibitory effect on the symptoms of blight disease on tomato leaf compared with the control. The better protection efficacy against B. cinerea on tomato leaf was observed with the culture filtrates of S. philanthi RM-1-138 (82.89% and 0.33 cm 2 lesion areas symptoms). Moreover, the antifungal compounds in the culture filtrate of S. philanthi RM-1-138, identified by GC-MS, were greatly altered relative to concentration components under different temperatures and light/dark conditions tested. Our results clearly demonstrated that the environmental factors have an influence on antifungal activity of the three strains of Streptomyces spp.

Aims The study reports the antifungal and antiaflatoxigenic mechanism activity of freeze-dried culture filtrate of Streptomyces philanthi RL-1-178 (DCF RL-1-178) against two aflatoxigenic strains (Aspergillus parasiticus and A. flavus) and identification of its active component. Methods and Results Significant inhibition in ergosterol biosynthesis by the DCF RL-1-178 appeared on the plasma membrane. Moreover, the DCF RL-1-178 showed dose-dependent inhibition of methylglyoxal (MG) (an aflatoxin inducer) biosynthesis and exhibited a novel antiaflatoxigenic action mechanism. Significant impairments in enzymatic [superoxide dismutase (SOD) and catalase (CAT)] and nonenzymatic [oxidized and reduced glutathione (GSH) and ratio of oxidized and reduced glutathione (GSSG)] anti-oxidative defense molecules were observed in the two aflatoxigenic cells. The active component of the DCF RL-1-178 was identified as natamycin. The natamycin exhibited against A. parasiticus and A. flavus with the minimum inhibitory concentration (MIC) values of 0.5 and 1.0 µg ml−1, respectively, while the minimum fungicidal concentration values were the same (4.0 µg ml−1). Conclusions The DCF RL-1-178 containing natamycin exhibited the following effects: (1) inhibition of cellular ergosterol biosynthesis on plasma membrane, (2) reduction in MG (aflatoxin inducer) confirmed novel antiaflatoxigenic mechanism of action, and (3) caused remarkable debasement in antioxidant defense enzymes (SOD and CAT) and nonenzymatic defense molecules (GSH and GSSG) revealing biochemical mechanism of action.