Impact of environmental factors on Streptomyces spp. metabolites against Botrytis cinerea.

Botrytis cinerea is an economically important disease on numerous vegetables including tomato. From our previous studies, a spore suspension of Streptomyces philanthi RL-1-178 and RM-1-138 and Streptomyces mycarofaciens SS-2-243 showed strong inhibition against B. cinerea. In this study, the efficacy of their antifungal metabolites against B. cinerea was investigated after enhancing the production through the optimum culture medium and environmental conditions (temperature, light/dark cycle). In vitro studies indicated that glucose yeast-malt (GYM) agar and incubation at 28°C were optimal for growth and mass spore production of all three Streptomyces strains. Moreover, light/dark conditions had a positive effect on the growth and spore production of S. philanthi RM-1-138 and RL-1-178 but not on S. mycarofaciens SS-2-243. Both strains of S. philanthi possessed an antifungal activity against B. cinerea (100% inhibition) while S. mycarofaciens showed different results on PDA (83% inhibition) and GYM (88% inhibition) at the optimum incubation temperature at 21°C. The antifungal compounds from S. philanthi RM-1-138 exhibited the highest protection efficacy against B. cinerea on tomato leaves (82.89% and 0.33 cm2 lesion areas symptoms). The antifungal compounds RM-1-138, identified by GC-MS, were greatly altered based on components concentration under various temperatures and light/dark conditions. The anti-B. cinerea of S. philanthi RM-1-138 was established at a higher level in several metabolic compounds in the dark condition (11 and 32 antifungal compounds after incubation at 21°C and 28°C, respectively) than in the light condition (11 and 19 antifungal compounds after incubation at 21°C and 28°C, respectively). At 21°C, the dominant component was acetic acid (67.41% and 68.77% in light and dark conditions, respectively) while at 28°C, benzeneacetamide (43.58% in light) and propanamide (20.68% in the dark) were dominant. The results clearly demonstrated the significant influence of environmental factors on the production of antifungal metabolites of Streptomyces spp.

Utilization of palm oil mill effluent as a novel substrate for the production of antifungal compounds by Streptomyces philanthi RM-1-138 and evaluation of its efficacy in suppression of three strains of oil palm pathogen.

AIMS: This study aimed to use palm oil mill effluent (POME) as a renewable resource for the production of antifungal compounds by Streptomyces philanthi RM-1-138 against Ganoderma boninense, Ceratocystis paradoxa and Curvularia oryzae. METHODS AND RESULTS: The efficacy of antifungal compounds RM-1-138 against the three strains of fungal oil palm pathogen was evaluated both in vitro and on oil palm leaf segments. In vitro studies using confrontation tests on glucose yeast-malt extract (GYM) agar plates indicated that the strain RM-1-138 inhibited the growth of all three fungal pathogenic strains. The antifungal compounds produced in the GYM medium exhibited significantly higher inhibition (79%-100%) against the three fungal pathogens than using the diluted POME (50%) medium (80%-83% inhibition). The optimum condition for the production of antifungal compounds from the strain RM-1-138 was as following: POME of 47,966 mg L-1 chemical oxygen demand (COD), the initial pH at 7.0 and supplemented with yeast extract (0.4%). Meanwhile, severe morphological and internal abnormalities in C. oryzae hyphae were observed under a scanning electron microscope and transmission electron microscope. In vivo experiment on oil palm leaf segments indicated that the efficacy of the antifungal compounds RM-1-138 (DSI = 1.3) were not significantly difference in the suppression of Curvularia leaf spot compared with the two commercial chemical fungicides of mancozeb® (DSI = 1.0) and tetraconazole® (DSI = 1.3). CONCLUSIONS: Antifungal compounds produced by S. philanthi RM-1-138 grown in POME have the potential to inhibit fungal pathogens. SIGNIFICANCE AND IMPACT OF THE STUDY: The POME (about 47 mg L-1 COD) with the initial pH of 7.0 and supplementation of 0.4% nitrogen could be used as a culture medium for the growth and production of antifungal compounds of S. philanthi RL-1-138. In addition, the antifungal compound RM-1-138 could suppress the three strains of oil palm fungal pathogen tested on oil palm leaf segment.