Production of poly(β-hydroxybutyric acid) and exopolysaccharide by Azotobacter beijerinckii WDN-01

Abstract

The physico-chemical factors influencing the production of poly(β-hydroxybutyric acid) [PHB] and exopolysaccharide (EPS) by a yellow pigmented Azotobacter beijerinckii strain WDN-01 were investigated. Under N-free condition with excess carbon, PHB accumulation attained its maximum at the late exponential phase followed by a sharp decline while EPS production was more or less parallel with growth. Polymer synthesis, however, was carbon-source-specific, the highest yield of PHB (2.73 g/l) and EPS (1.5 g/l) was obtained with 3% (w/v) glucose and mannitol respectively. Organic N-sources enhanced PHB production significantly, but inorganic nitrogenous compounds were inhibitory to both PHB and EPS synthesis. At optimum K2HPO4 concentration, the polymer yield was attributed to biomass yield. Oxygen-limiting conditions, irrespective of carbon sources favoured production of PHB and EPS.