Microwave induced mutagenesis of Lactobacillus casei subsp. rhamnosus for enhancing L-lactic acid production

Mutagenesis of Lactobacillus casei subsp.rhamnosus X1-12 after low power microwave irradiation was investigated.Under a microwave power of 400 W and irradiation length of 3 min,a mutated strain W4-3-9 with high-yield L-lactic acid was obtained by screening.Compared with the starting strain X1-12,the L-lactic acid production of W4-3-9 was increased by 58.0% at a concentration of 115.8 g/L.The strain maintained the capability of producing a high L-lactic acid level after 10 generations.Cell surface morphology and DNA structures of parental and mutated strains were observed by atomic force microscopy (AFM).Amplified fragment length polymorphism (AFLP) analysis suggested the difference in AFLP band pattern between the mutated and non-mutated strains.Sequencing and BLAST analysis revealed that the catalytic site of lactate dehydrogenase (DHL) was changed due to the microwave induced mutation.