Tuesday, April 30, 2013
Exhibit Hall
Bacillus subtilis strain MR4 carrying a mutation in ldh (L-lactate dehydrogenase; L-LDH) and alsS (acetolactate synthase; butanediol pathway) was engineered to produce D-lactic acid by integrating ldhA (D-lactate dehydrogenase; D-LDH) from Lactobacillus bulgaricus into the chromosome of B. subtilis (MR4-1). In this construct, the L. bulgaricus ldhA was expressed from the ldh promoter of B. coagulans P4-102B. In pH-controlled fermentations, strain MR4-1 produced D-lactic acid at a titer of about 55 g/L in about 120 hours and the yield of D-lactic acid from glucose was about 95%. To increase the productivity and titer of D-LA, ldhA gene from B. coagulans was investigated. B. coagulans ldhA expressed from its own promoter, although readily supported lactate production in Escherichia coli, was poorly expressed in strain MR4. In order to evaluate the differences between the two, expression level of the ldhA gene from the two promoters as well as the biochemical properties of D-LDH from L. bulgaricus and B. coagulans were determined. Results from these experiments are presented and discussed towards developing a B. subtilis strain for production of D- lactate at high titer and yield as a feedstock for bio-based, renewable, plastics.