Isolation of alkaliphilic bacteria for production ofhigh optically pure l-(+)-lactic acid

Abstract

Lactic acid bacteria that grow under alkaline conditions (pH 10) were isolated from various sources in Okinawa (Japan). These alkali-tolerant and alkaliphilic bacteria were classified as follows: Microbacteriumsp. (1 strain), Enterococcus spp. (9 strains), Alkalibacterium spp. (3 strains), Exiguobacteriumspp. (5 strains), Oceanobacillus spp. (3 strains) and Bacillus spp. (7 strains) by 16S rRNA gene sequencing. By fermentation, many strains were able to convert glucose into mainly L-(+)-lactic acid of high optical purity in alkaline broth. This result indicated that valuable L-(+)-lactic acid-producing bacteria could be isolated efficiently by screening under alkaline conditions. Six strains were selected and their ability to produce lactic acid at different initial pH was compared. Enterococcuscasseliflavus strain 79w3 gave the highest lactic acid concentration. Lactic acid concentration and productivity were 103 g L-1 (optical purity of 99.5% as L-isomer) and 2.2 g L-1 h-1, respectively when 129 g L-1 of glucose was used by batch fermentation.