1株高产L-乳酸菌株的分离鉴定及其发酵培养基优化

Isolation and Identification of a Strain for High-Yield Production of L-Lactic Acid and Optimization of Its Culture Medium

从辣白菜样品中筛选出1株高产乳酸的菌株LB-103,经L-/D-乳酸试剂盒检测该菌株发酵产L-乳酸的光学纯度为100%。通过形态学观察、VITEK 2生理生化鉴定和16S r DNA序列分析,确定该菌株为鼠李糖乳酸杆菌(Lactobacillus rhamnosus),将其命名为鼠李糖乳酸杆菌DLF-15038。对其发酵培养基进行初步优化,发现廉价的棉籽饼粉可以部分替代酵母粉,采用15 g/L棉籽饼粉和10 g/L的酵母粉为复合氮源,L-乳酸的产量得以维持且明显降低成本,最适无机盐质量浓度分别为CH_3COONa 3 g/L、KH_2PO_4 2 g/L、MnSO_4 0.3 g/L、MgSO_4 0.2 g/L。在该优化条件下,进行了5 L发酵罐中的批式流加发酵实验,发酵72 h,L-乳酸产量为165.15 g/L,生产强度为2.29 g/(L·h),糖酸转化率为93.34%。

A strain,LB-103,which is capable of producing high concentration of L-lactic acid with high optical purity was isolated from kimchi.The optical purity of the produced lactic acid was measured to be100%by using L-/D-lactic acid enzymatic test kit.The strain was identified as Lactobacillus rhamnosus based on its morphological features,physiological and biochemical properties(VITEK2automated microbial identification system),and16S rDNA sequence analysis.It was named L.rhamnosus DLF-15038.Then the fermentation medium for L-lactic acid production was optimized,and the results showed that yeast extract(10g/L)and cottonseed meal(15g/L)were used as nitrogen sources to maintain high L-lactic acid yield and simultaneously reduce the cost.The optimal concentrations of inorganic salts in the medium were as follows:CH3COONa3g/L,KH2PO42g/L,MnSO40.3g/L and MgSO40.2g/L.Finally,fed-batch fermentation was performed under the optimized conditions in a5-L fermentor.We obtained165.15g/L L-lactic acid after72h fermentation by using the strain DLF-15038,with a yield of93.34%(g L-lactic acid/g glucose),and a productivity of2.29g/(L·h).