Breeding of a Lactobacillus rhamnosus Strain with the High Yield Fermentation of L-Lactic Acid

A high yield mutant strain of lactic acid fermentation,defined as SCT-10-10-60,was selected by mutagensis of Lactobacillus rhamnosus JCM1553 strain with the combination of UV and Co60 radiation.The result of 77 generation transfer culture verified the strain had the genetic stability on lactic acid fermentation.In the shave flask fermentation with glucose as substrate under the condition of 37℃,200rpm,the lactic acid concentration of mutant strain in broth was reached to maximum of 195.67g/L at 60h of fermentation and the maximum ratio of glucose converting to lactic acid reached to 95.33%.The maximum lactic acid yield,the fermentation rate and the ratio of glucose converting to lactic acid of mutant strain were respectively 16.24%,50.13% and 17.81% higher than that of start strain.In the fermentation with enzymatic hydrant of cassava starch as substrate under the same condition,the lactic acid concentration of mutant strain was reached to 203.33g/L of maximum at 84h fermentation,with the maximum lactic acid yield and the fermentation rate of mutant strain both 29.49% higher than that of start strain(157.02g/L,84h),and the maximum ratio of glucose converting to lactic acid reached to 78.85%,24.53% higher than that of start strain(63.32%).The L-lactic acid concentration in the fermentation product of mutant strain,determined by using chiral column HPLC,was high to 96.75% and had not statistical significant difference with the start strain(96.97%),indicating that SCT-10-10-60 was a L-lactic acid high-yield strain.However,the calculation of L-lactic acid yield per cell biomass showed that the L-lactic acid yield of mutant strain was improved by enhancing the rate of cell increment.Since SCT-10-10-60 strain has more advantage features than current industrial strains in L-lactic acid fermentation,it is thought as a potential strain for L-lactic acid production.