Screening of Lactobacillus rhamnosus strains mutated by microwave irradiation for increased lactic acid production

The present study focused on using microwave radiation to produce mutant strains ofLactobacillus rhamnosus with increased lactic acid production. At microwave radiation frequency 2450-MHz and irradiation time 3 min, an L (+)-lactic acid high-yield mutant, W4-3-9, was obtained. With glucose as the sole carbon source, production of lactic acid and L-(+)-lactic acid by the W4-3-9 strain was 1.5-fold greater than that of the parent strain. The mutant was stable for increased L-lactic acid production for at least 9 generations. Results of amplified fragment length polymorphism analysis suggest that mutations of malate/lactate dehydrogenase and pyruvate kinase genes are the possible cause of the increased production of lactic acid in W4-3-9. We believe that microwave irradiation could be an efficient method for inducing microbial mutagenesis.   Key words: Lactobacillus casei subsp. rhamnosus CICC 6013, mutation, L-lactic acid, microwave irradiation, amplified fragment length polymorphism.