Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 8, 1997
Publication Date: N/A
Technical Abstract: Lactic acid, which is commonly used as a food acidulant, preservative, and flavor agent, has recently gained popularity for the production of biodegradable polymers. While this organic acid can be produced chemically as a racemic mixture, it is often desirable to use fermentation in order to produce optically pure product. This is especially important for food use where only biologically metabolizable L-lactate can be used. Production o poly (lactate) also requires that the lactic acid feedstock be as stereo chemically pure as possible. The filamentous fungus Rhizopus oryzae has often been used for industrial production since it produces optically pure L-(+)-lactic acid and has only minimal growth requirements. The greatest production of the acid occurs during aerobic growth from lactate dehydrogenase mediated reduction of pyruvate. With anaerobic conditions, very little lactic acid is produced and the primary fermentation product is sethanol. We have used nitrosoguanidine mutagenesis and selective screenin to obtain mutants with impaired alcohol dehydrogenase (Adh) activity. By minimizing the regeneration of NAD+ through ethanol fermentation, carbon flow can be diverted to lactic acid production. One of these mutants expressed only 5% of the wild-type Adh activity under anaerobic stress and produced nearly 4% lactic acid in 70 hours. This is almost a 10-fold increase when compared to production by the parent strain. Eliminating the need for aeration should result in a considerable savings in the production of lactic acid. Further results on the improvement of this and other strains will be presented.