科研之友
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摘要
Shikimic acid resistance and addition to enhance immunosuppressant ascomycin production were investigated in this study. A shikimic acid resistant strain SA68 was obtained with ascomycin production of 330 mg/L, displaying approximately 22% increment compared with the parental strain FS35 (270 mg/L). Under the optimal condition of 3 g/L shikimic acid added at 24 h, ascomycin production was further increased by 36%, reaching 450 mg/L. To get deep insights into the effects of shikimic acid resistance and addition on ascomycin biosynthesis, fermentation properties, enzymes activities, metabolites and genes transcriptional levels were analyzed and evaluated. The potential targets were revealed for higher ascomycin production, which were the amplification of carbon flux toward shikimic acid by enhancing 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (DAHPS) activities and eliminating the feedback inhibition of aromatic amino acids on DAHPS activities, and the elevation of FkbO activities by amplifying fkbO gene to increase the flux of shikimic acid to chorismic acid further to 4,5-dihydroxycyclohex-1-enecarboxylic acid in Streptomyces hygroscopicus var. ascomyceticus. The results indicated that the developed methods would be helpful for ascomycin large scale fermentation. Moreover, the potential targets revealed in this study are valuable to engineer the higher-yield ascomycin-producing strain, as well as other analogous macrolide compounds-producing strains.
