Submitted to: Great Lakes Regional American Chemical Society Symposium
Publication Type: Abstract Only
Publication Acceptance Date: October 20, 2004
Publication Date: October 20, 2004
Citation: Dien, B.S., Whitehead, T.R., Nichols, N.N., Skory, C.D., Cotta, M.A. 2004. Recombinant biocatalysts for converting sugar mixtures to lactic acid [abstract]. Great Lakes Regional American Chemical Society Symposium. Paper No. 40. Technical Abstract: Lactic acid is used as a feedstock for production of PLA-based plastics and for production of ethyl lactate. Currently, lactate is produced from starch either using lactic acid producing bacteria or the fungus Rhizopus oryzae. Conversion of lignocellulose to lactic acid requires strains capable of fermenting mixtures of hexose and pentose sugars. Previously, we have reported on Escherichia coli strains capable of converting glucose to L-lactic acid with yields up to 93% of theoretical. We have now developed the Gram negative bacterium Klebsiella oxytoca as a host for lactate production from lignocellulosic biomass. K. oxytoca is well suited for fermentation of lignocellulose hydrolysates because the bacterium naturally grows in paper sulfite streams and ferments a wide variety of hexoses and pentoses as well as cellobiose and short xylan oligomers. We have transformed and expressed a lactate dehydrogenase (ldh) gene from Streptococcus bovis into K. oxytoca strain MA51. The transformed strain fermented glucose to L-lactic acid at a maximum yield of 0.82 g/g. The strain also converted cellobiose and xylose to lactic acid; however, yields were much lower because of production of alcohols. Yields of lactic acid from xylose were subsequently improved from 0.36 g/g to 0.88 g/g by selecting for a mutant with reduced alcohol dehydrogenase activities.