Submitted to: Society of Industrial Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: August 6, 1999
Publication Date: N/A
Technical Abstract: There has been renewed interest in producing lactate by fermentation because of the possibility of using lactate as a monomer for biodegradable plastics. Currently, most lactate is produced from fermenting glucose. We are investigating lignocellulosic biomass as an alternative, less expensive source of fermentable sugars. Lignocellulosic biomass contains a mixture of sugars including glucose and xylose. Converting biomass to lactate, therefore, requires a microorganism capable of using pentoses as well as glucose. Those lactate fermentative bacteria that do ferment pentoses usually produce significant amounts of acetate and a mixture of L- and D- lactate. We have constructed three recombinant Escherichia coli strains suitable for converting lignocellulosic hydrolysates to lactate because they ferment hexoses and pentoses almost exclusively to lactate. The lactate producing strains were constructed from E. coli strains that have been mutated so as to render them incapable of fermentative growth. We transformed these strains with a plasmid containing the lactate L-dehydrogenase gene from Streptococcus bovis. The resulting strains grow anaerobically and produce lactate. Furthermore, because lactate dehydrogenase activity is required for fermentative growth, the plasmid is maintained in the absence of antibiotic as long as the cells are cultured anaerobically. When one of the strains was used to ferment glucose and xylose, in pH controlled batch cultures, the cultures produced 0.75 g lactate per g sugar consumed. We are currently characterizing each lactate producing strain for lactate productivity and tolerance.