Hyperproduction of poly-β-hydroxybutyrate during exponential growth of Azotobacter vinelandii UWD

Abstract

The transformation of Azotobacter vinelandii UW with A. vinelandii 113 DNA resulted in the formation of rifampin-resistant colonies, 13% of which also inherited a previously unrecognized mutation in the respiratory NADH oxidase. These transformants produced colonies with a white-sectored phenotype after prolonged incubation. Cells from these sectors were separated and purified by streaking and were named UWD. The dense white phenotype was due to the production of a large amount of poly-β-hydroxybutyrate during the exponential growth of strain UWD. The polymer accounted for 65 or 75% of the cell dry weight after 24 h of incubation of cultures containing glucose and either ammonium acetate or N2, respectively, as the nitrogen source. Under the same conditions, strain UW cells contained 22 to 25% poly-β-hydroxybutyrate, but O2-limited growth was required for these optimal production values. Polymer production was not dependent on O2 limitation in strain UWD, but the efficacy of conversion of glucose to poly-β-hydroxybutyrate was enhanced in O2-limited cultures. Conversion efficiencies were >0.25 and 0.33 mg of poly-β-hydroxybutyrate per mg of glucose consumed under vigorous- and low-aeration conditions, respectively, compared with an efficiency of 0.05 achieved by strain UW. Strain UWD, therefore, appeared to form poly-β-hydroxybutyrate under novel conditions, which may be useful in designing new methods for the industrial production of biodegradable plastics.