Isolation of Lactobacillus spp. from diverse environmental sources and strain improvement for increased production of D-lactic acid

초록

Lactic acid and its derivatives are widely used in the food, pharmaceutical and cosmetic industries. It is also a major raw material for the production of poly lactic acid (PLA), a biodegradable and environment-friendly polymer, which could be a replacement for synthetic plastics derived from petroleum. In this study, for the production of D-lactic acid by Lactobacillus spp., diverse samples were screened for new lactobacilli isolates using selective (Rogosa) medium. Over 149 isolates were isolated from human vagina and saliva, soil, water, plain yogurt, shellfishes and kimchi. D-lactic acid production by individual isolates was examined using HPLC analysis with Chiralpak MA column and UV detector. PCR amplified ldhD gene from Lactobacillus rhamnosus ATCC53103 was cloned using a Lactobacillus/E. coli shuttle vector, pTRKH2. pTRKH2::ldhD was constructed using enzyme restriction and ligation, and was introduced into L. plantarum, L. paracasei, and L. gasseri by electroporation for over-expression of D-lactic acid. Transformants were confirmed by colony PCR method and compared with its wild types in growth and pH change. In several transformants, D-lactic acid production was increased up to 50% compared to that of wild types. This study confirms the potential of strain improvement for the production of renewable resources such as D-lactic acid.