L-乳酸米根霉发酵体系LDH活力及代谢调控研究

Study on Lactate Dehydrogenase Activity of Rhizopus oryzae Fermentation System and Its Metabolic Control

乳酸脱氢酶(LDH)是米根霉代谢生产L-乳酸过程的关键酶,研究其在发酵过程中的活力变化,从酶水平分析发酵条件对L-乳酸发酵的影响,对米根霉发酵生产L-乳酸的人工代谢调节、菌种选育具有重要意义。本文研究了摇瓶条件下的米根霉AS3.1208发酵体系中乳酸脱氢酶的活力调控条件及与L-乳酸即时产率的关系,结果表明,发酵体系中L-乳酸产率与LDH活力在36～40h时最高。葡萄糖作为C源的L-乳酸产率与LDH活力比甘薯淀粉高。与牛肉膏和蛋白胨相比,硫酸铵是米根霉代谢的最佳N源,0.40%的硫酸铵具有较高的乳酸产率与LDH活力。发酵培养基中添加CaCO3与否,对乳酸产率与LDH活力有极大影响。以甘薯淀粉为碳源,在250ml三角瓶中的装液量为100ml,发酵36～40h时的L-乳酸即时产率最大,此时LDH活力也最高。

Lactate dehydrogenase (LDH) is a key enzyme that catalyzes the transformation of L-lactic acid from pyruvate in Rhizopus oryzae. Investigations of its activity during the fermentation have important significances on metabolic engineering and strains selection for increasing lactate production. In this study, the relationship between LDH activity and L-lactic acid production rate of Rhizopus oryzae AS3.1208 in shaking flask was investigated. The results indicated that glucose as carbon source had a higher L-lactic acid production rate and LDH activity than the sweet potato starch source. (NH4)2SO4 was the optimum nitrogen source compared with beef extract and peptone. It had the highest L-lactic acid production rate and LDH activity at a concentration of 0.40%. The addition of CaCO3 to fermentation medium for the neutralization of lactic acid produced had an absolute effect on lactate production as well as LDH activity. A higher L-lactic acid production and LDH activity could be achieved at 36～40h fermentation when the 250ml flask was filled by 100ml fermentation liquid with sweet potato starch as carbon source.