Submitted to: Society of Industrial Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: July 27, 2000
Publication Date: N/A
Technical Abstract: Lactic acid has long been used in the food and pharmaceutical industry for a diverse array of specialized purposes. Recent ecological interests have fueled the demand of lactic acid for the manufacture of the biodegradable plastic, polylactic acid (PLA) and "green-solvent," ethyl lactate. The global lactic acid market is estimated to be in excess of 100,000 tons per year and is expected to increase substantially in the next few years as ne PLA facilities become operational. However, fermentation efficiency must be improved to ensure the economic feasibility of these anticipated market expansions. The fungus Rhizopus oryzae is often preferred for industrial fermentations because of the ability to produce large amounts of optically pure L-(+)-lactic acid in a minimally defined medium. We have cloned the lactate dehydrogenase gene, ldhA, from R. oryzae and developed genetic transformation methods for stable chromosomal integration. The introduction of multiple copies of ldhA into R. oryzae has resulted in a substantial increase in Ldh activity. Recombinant strains are capable of more rapid fermentations and achieve higher yields of lactic acid than the parental wild-type fungus. This increase is associated with a concomitant decrease in both ethanol and fumarate.