Polymer production by a mucoid stain of Azotobacter vinelandii in batch culture

Abstract

In this study, some factors influencing the secretion of alginic acid and the accumulation of poly-β-hydroxybutyrate (PHB) by a highly mucoid strain of Azotobacter vinelandii were investigated in batch culture. The highest alginate yields (6.0–7.5 mgml-1 culture supernate) were routinely obtained for growth in a phosphate and nitrogen-rich medium (PNR) with glucose as carbon source, aerated by shaking at 280 rpm. In this case, the intracellular accumulation of PHB reached a maximum of 30% cell dry weight. At 120 rpm alginate yield was only 1.4 mgml-1 and PHB constituted 40%. This reflected oxygen-limitation under these conditions. The presence of inorganic phosphate in PNR was seen to be important as growth in low-salts, nitrogen-free medium resulted in poor alginate production, which was not improved by addition of nitrogen sources, such as nitrate or glutamate. Under otherwise optimised conditions, different peptones gave widely different alginate yields. If glucose was replaced by sucrose, growth and alginate production were reduced.