米根霉产L-乳酸耐温菌株的^(60)Co-γ射线诱变选育

^(60)Co-γ Irradiation Mutation and Screening of Heat-resistant Rhizopus oryzae Mutant Producing L-Lactic Acid

目前产L-乳酸的米根霉菌株的最适发酵温度为32℃,该温度较低,不利于产物分离且易染杂菌。以米根霉As3.819为出发菌株,采用60Co-γ射线进行诱变处理,以正突变率为指标,诱变剂量为400Gy,通过筛选得到耐38℃高温的5号突变株mut-5,经连续传代7次,遗传性状稳定。与出发菌株相比,发酵72h后,mut-5突变株发酵液中的乳酸含量提高了24.15%,乙醇含量降低了9.27%。乳酸脱氢酶(LDH)比活力提高了39.41%,乙醇脱氢酶(ADH)比活力有所下降,而对还原糖的利用速率以及生物量的积累均高于出发菌株。

The optimum temperature for Rhizopus oryzae fermentation is 32℃, but it is difficult to separate lactic acid and easy to be contaminated by other bacteria at this low temperature. A Rhizopus orzae mutant, mut-5, which was resistant to high temperature of 38 ℃ and still has stable genetic character after continuous 7 passages, was screened out by ^60Co-γ irradiation at 400 Gy that gave a perfect positive mutation rate. Compared with the parent strain, the L-lactic acid concentration in broth fermented by the mut-5 for 72h increases by 24.15 %, and the ethanol concentration decreases by 9.27 %. The specific activity of lactate dehydrogenase （LDH） of the mut-5 up to 39.41%, while the specific activity of alcohol dehydrogenase （ADH） falls down. In addition, the mut-5 has a higher reducing sugar consumption rate and biomass accumulation than the parent strain.