Submitted to: Society of Industrial Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: August 6, 1999
Publication Date: N/A
Technical Abstract: The global lactic acid market is estimated to be in excess of 100,000 tons per year with anticipated growth for developing markets that include the non-chlorinated solvent, ethyl lactate, and the biodegradable plastic, polylactide (PLA). Rhizopus oryzae is often preferred for manufacturing high quality lactic acid, because it synthesizes only stereo-chemically pure L-(+)-lactic acid and has minimal growth requirements, allowing for improved product clean-up. Recently we have studied the control and production of lactic acid, in addition to several unwanted metabolites. Achieving mitotically stable transformants in the zygomycetes fungi, Rhizopus, Mucor, and Phycomycetes has always been difficult because transformed plasmids rarely integrate, and their autonomous replication is unstable. A transformation system that we developed seems to avoid these problems because transformed DNA appears to integrate in a stable fashion. This important technique will finally give us the ability to not only increase expression of specific genes but also to eliminate others by site-specific integration. Numerous genes that are involved in the metabolic pathways of R. oryzae have been isolated and studied to allow us to identify several targets for improving lactic acid production. Preliminary data with several of our metabolically engineered strains confirm that we are able to direct the synthesis of various fermentation products.