| Turpan Depression and Tarim Basin are respectively located in the eastern and southern Xinjiang and featured with the arid climate and water shortage, forming extreme niches, such as the Gobi, deserts and salt lakes. Our previous research indicated that abundant, diverse, and rare actinomycetes are dwelled in these extreme niches. Herein, we performed strain identification of actinomycetes isolated from Turpan Depression and Tarim Basin using polyphasic taxonomy methods, and screened out actinomycete strains with antifungal bioactivities. Pure compounds with strong antifungal activity and new structures were isolated from strains with bioactivity. Fermentation conditions of these strains were optimized, and the yield of active product was significantly increased. The antifungal mechanism of oxanthromicin against Verticillium dahliae was investigated. Detailed research progress is included: 1. Strain identification of actinomycetes from Turpan Depression and Tarim BasinMorphological, phylogenetic, physiological, and chemical characters of three actinomycete strains(TRM 46004, TRM 46074 and TRM 155-22) isolated from Turpan Depression and Tarim Basin were described in detail and identified using polyphasic taxonomy methods. The data showed that strain TRM 46004 and TRM 46074 belong to the family of Pseudonocardiaceae, with a high level taxonomic status of genus. A new genus Longimycelium was established for strain TRM 46004, which was named as Longimycelium tulufanense TRM 46004 T and considered as the type species of this genus. Another new genus Streptopolyspora was created for strain TRM 46074, which was is designated as Streptopolyspora aydingkolensis TRM 46074 T. A new species Streptomyces alarensis was also designated for strain TRM 155-22. 2. Purification and structural elucidation of compounds from actinomycetes withantifungal activityEighty-six actinomycete strains isolated from Turpan Depression and Tarim Basin were investigated for their bioactivity against Verticillium dahlia, a pathogen for cotton verticillium wilt, using confrontation method and agar diffusion method. Our data showed that 11 strains among of them have obvious inhibitory activity on the growth of V. dahlia, including the new species S. alarensis TRM 155-22. Subsequently, we conducted chemical analysis of its secondary metabolites. Compound with antifungal activity against V. dahlia were extracted and identified as oxanthromicin. Meanwhile, two compounds with new structure were obtained. 3. Optimize the fermentation medium and conditions for oxanthromicin by Statistical methodsStatistical methods such as Single Factor, Plackett-Burman design, and Response Surface methodology were employed to optimize the fermentation medium and conditions for S. alarensis TRM 155-22. Finaly, the optimal fermentation medium and condition were determined, and the yield of oxanthromicin was increased for 4.6-fold to 128.5 mg/L. 4. Antifungal mechanism of oxanthromicin against Verticillium dahliaeThe antifungal activity of oxanthromicin against V. dahliae and the underlying mechanism were investigated. Oxanthromicin substantially suppressed spore germination, mycelial growth, and biomass accumulation of V. dahlia. Electron microscopy and staining with propidium iodide and Rhodamine 123 indicated that oxanthromicin causes cell membrane damage and induces membrane potential changes in mitochondria. Ergosterol biosynthesis of V. dahlia was also shown to be inhibited by oxanthromicin. These results indicate that oxanthromicin exerts its fungicidal effect by disrupting fungal membrane structure.The present study showed that not only a number of novel actinomycetes are dwelled in the extreme niches of Xinjiang, but also some of them possess abundant secondary metabolites with excellent bioactivities. Our results enriched the understanding of extreme microorganism in Xinjiang and will facilitate the exploring and application of microbial resources from these extreme niches. |
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