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Abstract Lactic acid fermentation is a typical productinhibited bioconversion. The strains with improved performance of growing at low pH are desirable because low pH of the medium could increase the proportion of product in the freeacid form and contributes to the economics of the lactic acid purification process. The use of genome shuffling to improve the acid tolerance of an industrial strain of Labtobacillus casei was described. Two populations were obtained with subtle improvements by UV and NTG mutagenesis and were taken as the starters for genome shuffling. Parental protoplasts were inactivated and fused by polythyiene glycol 6000. The fusants grew at the RM plates were the shuffled strains. The shuffled strains after screening on low pH plate and CaCO3 plate were identified. The mutant strains were incubated in YE liquid medium at pH 3.8 and 3.4 as well as the wildtype. The mutant strains grew obviously better than the wildtype strain. Only the shuffled strains can grow under the condition of pH 3.4. The mutant strains and wildtype were both fermented at 37℃ for 48 h at pH 38. The production of Llactic acid of the mutant strain was 2.4 folds of the wildtype.
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Received: 09 February 2006
Published: 25 February 2006
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