Sunday, August 1, 2010
Pacific Concourse (Hyatt Regency San Francisco)
Succinic acid utilized as a precursor of many industrially important chemicals is a four-carbon dicarboxylic acid, biosynthesized as an intermediate of TCA cycle. Succinic acid is also produced as one of the fermentation products of anaerobic metabolism of various bacterial cells. In this study, in order to enhance the productivity of succinic acid, intensive and rational programs were performed for strain improvement with large amounts of mutated strains. Rapid and large screening process was possible by adopting a high throughput system(HTS) developed in our laboratory, which consists of CO2- and humidity-controlled incubator and 24-well microplate-culture system for miniaturized fermentations inside the incubator. Moreover, in order to develop an economic production medium, corn steep solid and corn steep liquor known as very cheap carbon- and nitrogen-sources were investigated, using statistical methods for medium optimization. Notably, it was found out that the production level of succinic acid was significantly enhanced by the optimal CO2-supply into the fermentation broth, demonstrating that CO2 gas mass-transfer rate(kLa) is a crucial factor in the succinic acid fermentation bioprocess. Therefore, through dynamic method based on the material balance of dissolved CO2, kLa values were measured according to impeller-agitation speed(rpm) and CO2-sparging rate(vvm) in a 5-liter stirred-bioreactor system, to determine the optimum range of kLa. Various results obtained from 5L- and 50L-scale anaerobic fermentor operations with sufficient level of dissolved CO2 will be presented in this paper as well.