Production of poly-beta-hydroxybutyrate by Azotobacter vinelandii strain UWD during growth on molasses and other complex carbon sources

Azotobacter vinelandii strain UWD formed greater than 2 mg/ml poly-beta-hydroxybutyrate (pHB) during exponential growth in media containing ammonium acetate and 1% w/v glucose, fructose, sucrose, or maltose, and greater than 1.5 mg/ml with 1% w/v sodium gluconate or glycerol. After acetate exhaustion, pHB formation accompanied carbohydrate utilization and pHB rapidly accounted for 53%-70% of the cell mass. Strain UWD also formed greater than 2 mg/ml pHB when it was grown with 2% w/v corn syrup, cane molasses, beet molasses, or malt extract. Beet molasses had a growth stimulatory effect which promoted higher yields of pHB/ml and a high ratio of pHB/protein. Malt extract also promoted higher yields of pHB/ml. In this case, pHB formation was no longer subject to acetate repression and the cells contained a higher ratio of pHB/protein. This study shows that unrefined carbon sources support pHB formation in strain UWD and that the yields of pHB were comparable to or better than those obtained with refined carbon sources.