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

Application of antifungal metabolites from Streptomyces philanthi RL-1-178 for maize grain coating formulations and their efficacy as biofungicide during storage

The major safety risk of maize grain is contamination with mycotoxins. In this study, a maize-coating formulation containing freeze-dried culture filtrate of Streptomyces philanthi RL-1-178 (DCF RL-1-178) was developed and evaluated to prevent the growth of mycotoxins during maize grain storage. In vitro studies using confrontation tests on PDA plates indicated that S. philanthi RL-1-178 inhibited the growth of Aspergillus parasiticus TISTR 3276 (89.0%) and A. flavus PSRDC-4 (95.0%). The maize grain coating formulations containing the DCF RL-1-178 (0, 5, 10, and 15% (v/v)) and the polymer polyvinylpyrrolidone (PVP-K90, 4.0% (w/v)) were tested for their efficacy in In vitro and during 5 months storage. In In vitro assay, maize coating formular containing the optimum concentration (15.0%, v/v) of the DCF RL-1-178 exhibited 54.80% and 54.17% inhibition on the growth of A. parasiticus TISTR 3276 and A. flavus PSRDC-4 respectively. The inhibition was also illustrated by the microstructures of interactions between the coated maize grains with or without the DCF RL-1-178 and the fungal pathogens observed under microscope and SEM. Incorporating the DCF RL-1-178 or fungicidal Metalaxyl® into the polymer PVP-K90 maize grains coating resulted in the complete inhibition of the production of aflatoxin B₁ (analysed by HPLC) by the two aflatoxigenic pathogens after 5 months storage at room temperature. However, the shelf-life was shortened to only 3 months during storage at room temperature with 90% relative humidity. Overall, the application of the 10-15% DCF RL-1-178 into the maize grain coating formular provides a new alternative measure to control the mycotoxins during storage for at least 5 months. The In vitro cell cytotoxicity study showed that a concentration of 15% (v/v) or 1000 μg/mL of the DCF RL-1-178 had a strong cytotoxic effect on Vero cells. These findings indicate that DCF RL-1-178 is a potential biofungicide for controlling mycotoxins contamination in maize seed storage for planting, but not maize grain storage for animal feed.

Efficacy of the antifungal metabolites of Streptomyces philanthi RL-1-178 on aflatoxin degradation with its application to prevent aflatoxigenic fungi in stored maize grains and identification of the bioactive compound

Aflatoxin B₁ is a potent carcinogen produced by Aspergillus flavus (A. flavus) and Aspergillus. parasiticus (A. parasiticus), mainly during grain storage. The efficacy of the freeze-dried culture filtrate of Streptomyces philanthi (S. philanthi) strain RL-1-178 (DCF) on degradation of aflatoxin B₁ (AFB₁) were evaluated and its bioactive compounds were identified. The DCF at a concentration of 9.0% (w/v) completely inhibited growth and AFB₁ production of A. parasiticus TISTR 3276 and A. flavus PSRDC-4 after 7 days tested in yeast-extract sucrose (YES) medium and on stored maize grains after 28 and 14 days incubation, respectively. This indicated the more tolerance of A. parasiticus over A. flavus. The DCF and bacterial cells of S. philanthi were capable to degrade AFB₁ by 85.0% and 100% for 72 h and 8 days, respectively. This confirmed the higher efficacy of the DCF over the cells. After separation of the DCF on thin-layer chromatography (TLC) plate by bioautography bioassay, each active band was identified by liquid chromatography-quadrupole time of flight mass spectrometer (LC-Q-TOF MS/MS). The results revealed two compounds which were identified as azithromycin and an unknown based on mass ions of both ESI⁺ and ESI^- modes. The antifungal metabolites in the culture filtrate of S. philanthi were proved to degrade aflatoxin B₁. It could be concluded that the DCF may be applied to prevent the growth of the two aflatoxin-producing fungi as well as the occurrence of aflatoxin in the stored maize grains.