Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/22/2005
Publication Date: 4/22/2005
Citation: Liu, S., Dien, B.S. 2005. Metabolic engineering of Lactobacillus brevis for ethanol production [abstract]. The World Congress on Industrial Biotechnology and Bioprocessing. p. 23.
Technical Abstract: Lactic acid bacteria (LAB) have GRAS (generally recognized as safe) status, and naturally occurring LAB have been successfully used in the fermentation industry. In recent years, genetically modified LAB have been explored for production of lactic acid, B-vitamins, and low-calorie sugar alcohols such as sorbitol and mannitol. LAB can grow at acidic pHs, and many strains are ethanol tolerant. These traits make LAB a favorable host for development as a biocatalyst for production of ethanol from lignocellulosic biomass. Conversion of lignocellulose to ethanol also requires microorganisms capable of fermenting both glucose and xylose sugars released from hydrolysis of lignocellulosic biomass. Many LAB can metabolize multiple sugars including pentoses, however, they produce large amounts of lactic acid in addition to ethanol. The objective of this study is to explore the possibility of re-directing the lactate fermentation capacity into ethanol production. A Lactobacillus brevis strain was chosen as a host for metabolic engineering that ferments both glucose and xylose. Although possessing several alcohol dehydrogenase enzymes, L. brevis does not have the required enzyme (pyruvate decarboxylase) needed for converting pyruvate into acetaldehyde. Introduction of a pyruvate decarboxylase gene from Gram-positive bacterium Sarcina ventriculi (Spdc) might increase carbon flow into ethanol. The recombinant Lactobacillus brevis strains were analyzed for ethanol and other metabolite products in pH controlled fermentations. An average of 2% (w/v) ethanol was produced by the recombinant strains. However, those strains also produced lactate at a molar ratio of ethanol to lactate of 1.10-1.14. Work is in progress to inactivate both D-ldh and L-ldh genes of the engineered L. brevis strains to further increase ethanol production.