Fungichromin production by Streptomyces sp. WP-1, an endophyte from Pinus dabeshanensis, and its antifungal activity against Fusarium oxysporum.

In this study, we isolated an endophytic Streptomyces sp. strain, WP-1, from surface-sterilized barks of Pinus dabeshanensis, an endangered Chinese plant. WP-1 showed strong antifungal activity against diverse pathogenic fungi, such as Fusarium oxysporum, Rhizoctonia solani, Phytophthora infestan, and Candida albicans. Based on phylogenetic analyses, preliminary identification suggested that the WP-1 strain belonged to the genus Streptomyces. Column chromatogram and HPLC were employed to isolate the primary antifungal component from the culture medium of WP-1, and it was identified as the methylpentaene macrolide antibiotic, fungichromin (FC). In this study, for the first time, using in vitro bioassay studies, we revealed that FC strongly inhibited mycelial growth and conidia germination in Fusarium oxysporum. The median inhibitory concentration of FC was found to be 3.80 mg/L. The fermentation conditions of the WP-1 strain were further investigated to improve FC production. We found that supplementation of the synthetic medium with oils (soybean oil, oleic acid, and so on), particularly during the initial stage of fermentation, significantly increased the FC yield. Ammonium-trapping agent (magnesium phosphate) was used as an additive to increase FC yield to 5741.7 mg/L. It was 2.9-fold more as compared to the highest FC yield reported so far where Streptomyces padanus PMS-702 was used for FC production. KEY POINTS: • Isolation and identification of a fungichromin-producing endophytic actinomycete WP-1 strain. • Fungichromin production was significantly improved via oils and ammonium-trapping agents addition. • Discovery of the antifungal activity of fungichromin against Fusarium oxysporum.

Diosgenin induces ROS-dependent autophagy and cytotoxicity via mTOR signaling pathway in chronic myeloid leukemia cells.

BACKGROUND: Diosgenin, a steroidal saponin isolated from legumes and yams, has been confirmed to possess potent anticancer effect on multifarious tumors including chronic myeloid leukemia (CML). PURPOSE: We aimed to further determine the anti-cancer activity of diosgenin and its mechanisms in CML cells. METHODS: The cell vitality was detected by MTT assay. Autophagic flux and reactive oxygen species (ROS) production were analyzed by laser scanning confocal microscope. Apoptosis was observed by flow cytometry. All proteins expression was examined by western blotting. RESULTS: Autophagy induction was demonstrated by examination of autophagic flux including autophagosomes accumulation, autophagosome-lysosome fusion and degradation of autophagosomes. Moreover, blocking autophagy with inhibitor chloroquine (CQ) and 3-methyladenine (3-MA), enhanced diosgenin-induced apoptosis, indicating the protective effect of autophagy in diosgenin-treated CML cells. Further study suggested that diosgenin-induced autophagy and cytotoxicity were accompanied by reactive oxygen species (ROS) generation and mammalian target of rapamycin (mTOR) signaling pathway inhibition. N-acetyl-L-cysteine (NAC) administration, a scavenger agent of ROS, could down-regulate diosgenin-induced autophagy via reversion of mTOR pathway inhibition. CONCLUSION: These results indicate that diosgenin obviously generates ROS and this oxidative pressure not only produces cytotoxic effect on CML cells but also induces autophagy. What's more, autophagy functions as a cytoprotective mechanism to overcome cytotoxicity of diosgenin in tumor cells and inhibition of autophagy can enhance the anti-CML activity of diosgenin.