Optimization Of Fermentation Conditions And Breeding Of High Producing Strain For A21978C

The A21978C group is lipopeptide antibiotics including daptomycin (C0) and itsderivatives (C1-5), which can kill Gram-positive bacteria. A21978C can be used in thetreatment of certain infections caused by gram-positive microorganisms. Due to low yield,it is difficult to achieve commercial production in China. In this work, the fermentationconditions were optimized for A21987C and the high productivity strain was selected. Theresearch conclusions are as follows:Streptomyces roseosporus NRRL11973can grow well on slants and shake flasks.A21978C of Streptomyces roseosporus NRRL11973is composed of four ingredients fromC0to C3. In high temperature, the structure of daptomycin is destroyed. Under alkalineconditions, the irreversible denaturation of daptomycin occurs and its antibacterial activitydisappears.The batch fermentation for A21978C production with Streptomyces roseosporus inshake flask was studied. The optimum medium for A21978C production was as follows:slant cultivation13days, inoculation amount6%, initial fermentation pH6~7,fermentation temperature28℃, rotation speed150r/min, loading volume50mL/500mLflask, soybean meal as nitrogen source, dextrin and starch as carbon sources.The effects of different precursors and key co-factors on the production of A21978Cwere evaluated. The results showed that capric acid affected the yield of A21978Csignificantly. The yield of A21978C increased26.3%, which added0.15g/L capric acidafter24hours of incubation. In conclusion, the yield of A21978C reached1261.9mg/Lunder optimal conditions, which was4.1-fold higher than that of primary fermentationconditions (306.9mg/L).Based on the previous optimization, UV mutagenesis treatment and streptomycinresistance plate screening methods were used to obtain a relatively highstreptomycin-tolerant strain. The yield of A21978C reached1388.1mg/L for the strainDY-4, which was a fusant of the high streptomycin-tolerant mutant and the original strainusing protoplasts fusion technology. The yield of A21978C for the strain DY-4was 1.21-fold higher than that of the original strain. Moreover, the strain DY-4is geneticallystable.