产朊假丝酵母利用有机酸的研究

Studies on Differential Uptake of Organic Acids by Candida utilis

在有机酸为唯一碳源的培养中培养产朊假丝酵母（Candida utilis）时，以L-苹果酸、乳酸、琥珀酸或柠檬酸为碳源的培养基经过48h后，有机酸浓度均由初始浓度5．0g／L下降到0．0g／L。以乙酸、草酸和富马酸为碳源的培养基有机酸浓度始终没有明显变化，说明产朊假丝酵母能够利用细胞外的L-苹果酸、乳酸、琥珀酸和柠檬酸，不能利用乙酸、草酸和富马酸。当葡萄糖和0苹果酸、乳酸、琥珀酸和柠檬酸中的某种有机酸共同做碳源时，葡萄糖浓度均可以在32h内从20．0g／L降到0．0g／L，而各有机酸在0～24h内浓度变化不大，24-48h浓度均有不同程度的下降，说明当培养基中有葡萄糖时，有机酸的利用受到抑制。当浓度均为2g／L的L-苹果酸、乳酸、琥珀酸和柠檬酸同时做碳源培养产朊假丝酵母时，乳酸大约经过40h浓度首先降到0．0g／L，L-苹果酸、柠檬酸、琥珀酸浓度在0～16h过程中没有明显变化，16～48h下降趋势明显，最后也都被菌体完全利用，说明乳酸比较容易被菌体利用，而L-苹果酸、琥珀酸和柠檬酸在被菌体利用先后顺序上没有明显区别。

Yeast species differ remarkably in their ability to degrade extracellular organic acids and to utilize them as their only source of carbon. The Concentration of L-malate, lactate, succinate or citrate decreased gradually, from 5.0 g/L to 0 g/L after 48 h, when Candida utilis was cultured in the culture medium, in which organic acid （L-malate, lactate, succinate or citrate） is the only source of carbon. But the concentration of xalate, acetate, tartrate and fumarate has no significant change. It was shown that Candida utilis could effectively utilize extracellular L-malate, lactate, succinate and citrate. However, xalate, acetate and fumarate could not be utilized by Candida utilis. The concentration of glucose decreased from 20g/L to 0g/L in 32 hours when glucose was used as the carbon source with any one from L-malate, lactate, succinate or citrate. But the concentration of L-malate, lactate, succinate or citrate has not changed evidently in the first 24 hours. However, the concentration decreased in the next 24 hours. It was shown that glucose inhibited the uptake of L-malate, lactate, succinate and citrate. When L-malate, lactate, succinate and citrate were used as the carbon sources together, the concentration of lactate decreased gradually from 2.0 g/L to 0 g/L after 40hours. The concentration of L-malate, succinate and citrate did not change evidently in the first 0- 16 hours but obviously decreased in the 16-48 hours. L-malate, succinate and citrate are used completely by Candida utilis and it had no obvious difference in the order of usage among them.