Isolation and characterization of bacterial producers of optically pure D(-) and L(+) lactic acid

Abstract

The aim of the present study was to isolate and characterize bacterial producers of optically pure D(-) and L(+) lactic acid for use in the synthesis of polymers employed in the production of resistive and biodegradable materials. Four hundred microorganisms were isolated. Of these strains, 20 had high capacity for production of only one lactic acid isomer which was selected for characterization. D(-) lactic acid producers were identified as Weissella paramesenteroides (25%), Leuconostoc mesenteroides (6.25%), Leuconostoc lactis (6.25%) and Lactobacillus delbrueckii (6.25%). L(+) lactic acid producers were identified as Lactobacillus casei (12.5%), Enterococcus sp. (18.75%), Lactobacillus paracasei (6.25%), Streptococcus sp. (6.25%) and Lactobacillus sp. (12.5%). The most promising isolate for L(+) lactic acid production was Ke8, in the presence of sucrose. Otherwise, Ke6 and Ke11 were the best producers, by using glucose as the carbon source. The best microorganism for the production of D(-) lactic acid was isolated from fermented milk (L. delbrueckii Y15C). However, the growth of this microorganism is easily inhibited on media containing sugar concentration greater than 60 g/L.