Growth Related Production of Poly-ß-Hydroxybutyrate by Azotobacter chroococcum Soil Isolate/Mutant using N, P, and Cane Molasses

Abstract

Soil isolate Azotobacter chroococcum ABR 51 produced a large amount of Poly-ß-Hydroxybutyrate (PHB) during growth in a chemically defined medium using cane molasses as carbon source. Nutritional requirements and cultural conditions for the optimal production of PHB by this strain under laboratory conditions were determined using inorganic, complex organic nitrogen sources, phosphate, and cane molasses. Among conventional carbon sources, (2% w/v) sucrose was found to be the preferred carbohydrate source by A. chroococcum ABR 51 for cell growth and PHB production (81.81%), followed by dextrose (78.09%) and commercial sugar (77.45%). Three percent of cane molasses concentration (w/v) had a growth stimulatory effect on PHB production, which was better than by sucrose and dextrose. Organic nitrogen compounds were preferred as nitrogen sources over inorganic nitrogen, maximum PHB yield of 75.86% was obtained with 0.2% yeast extract supplementation. Inorganic phosphate at a concentration suboptimal for growth had some growth promoting effect. The growth and PHB production were also dependent on oxygen limitation conditions. Therefore, use of unrefined carbon source like cane molasses along with optimized N- and P-supported PHB formation in the soil isolate of A. chroococcum ABR 51 is comparable with or better than that obtained with refined carbon sources like sucrose and dextrose. A mutant developed from ABR 51 was found to be a higher (2–9%) PHB producer, using different optimized nutrient sources, compared with the native soil isolate.