Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/8/2006
Publication Date: 12/8/2006
Citation: Liu, S. 2006. Developing gram-positive ethanologens [abstract]. International Symposium of Biocatalysis and Bioenergy. p. 33.
Technical Abstract: The microbial fermentation of almost all the C5 & C6 sugars to biofuel is vital to the overall economic conversion process from lignocellulosic biomass to ethanol. Currently available ethanologens can only use C6, not the mixture of C5 & C6, and relatively low concentrations of ethanol kill the fermenting microorganisms. The current ethanologens are also lacking in their resistance to fermentation inhibitors generated by biomass pretreatment. New strains need to be developed to ferment biomass hydrolyzate and achieve efficient conversion of C5 & C6 to fuel ethanol and chemicals. The rationale for exploring Gram-positive bacteria as second generation biocatalysts is their robust nature and stress tolerant traits plus the potential to ferment biomass derived-sugars. Gram-positive lactic acid bacteria (LAB) appear to be an attractive group of organisms to be modified for biomass conversion, since they are fermentative, have a GRAS (generally recognized as safe) status, are capable of metabolizing C5 & C6 sugars and are robust, tolerant of acidic pHs, and tolerant to high concentrations of sugars and ethanol. However, most LAB strains produce large amounts of lactic acid from pyruvate, and the carbon flow from pyruvate to ethanol is relatively weak, due to the lack of pyruvate decarboxylase gene. We have explored the possibility of re-directing the lactate fermentation capacity into ethanol production in several LAB strains. I will use a xylose fermenting strain, Lactobacillus brevis ATCC 367, to demonstrate the approach, and report fermentation analyses results and lessons learned. Additional strain improvement strategies leading to efficient biomass conversion will also be discussed.