Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/28/2006
Publication Date: 6/28/2006
Citation: Liu, S. 2006. Genetically engineered lactic acid bacteria for the production of fuels and chemicals [abstract]. 10th International Symposium on the Genetics of Industrial Microorganisms. Paper #015.
Technical Abstract: Economic conversion of abundant and renewable lignocellulosic feedstocks into biofuels and bioproducts will alleviate our dependence on petroleum. However, this will require microorganisms capable of fermenting both hexose and pentose sugars released by the hydrolysis of lignocellulosic biomass. Gram-positive lactic acid bacteria (LAB) appear to be an attractive group of organisms for strain development. LAB are capable of metabolizing multiple sugars, including pentoses. They are robust organisms, tolerant of acidic pHs and high concentrations of sugars and ethanol. LAB are also GRAS (generally recognized as safe). However, most LAB strains produce large amounts of lactic acid instead of ethanol from pyruvate, due to the lack of pyruvate decarboxylase (Pdc) gene. We have explored the possibility of re-directing the lactate fermentation capacity into ethanol production in several LAB strains. When a pdc gene from Zymobacter palmae was introduced into Lactococcus lactis, Pdc activity was elevated above background, but was lower than expected based on promoter activity. Recombinant strains produced enhanced yields of acetaldehyde, but not ethanol. This suggests that the Gram-negative pdc gene is not expressed well in L. lactis, and that the host strain lacks a functional acetaldehyde dehydrogenase (Adh). Therefore, a pdc gene was cloned from the Gram-positive bacterium Sarcina ventriculi and introduced into a host, Lactobacillus plantarum TF103, known to express high levels of Adh. In addition, in TF103 strain, both D-ldh and L-ldh genes are inactivated, which should favor the flow of carbon toward ethanol. Recombinant strain TF104, carrying the pdc gene from S. ventriculi grew faster than the parent strain and produced 90-158 mM ethanol. Current and future research directions will be discussed at the conference.