Poly-3-hydroxybutyrate production by Azotobacter chroococcum

Thirty-seven soil isolates and mutants of Azotobacter chroococcum tested fo r poly-3-hydroxybutyrate (PHB) production using Sudan black B staining meth od were found to be positive. One mutant showed a higher number of PHB-prod ucing cells and maximum number of granules per cell. Using 2 % glucose and 15 mmol/L ammonium acetate, PHB production was found to be maximum at 36 an d 48 h of growth under submerged cultivation and under stationary cultivati on, respectively. PHB production was found to be higher on sucrose and comm ercial sugar (as carbon sources) as compared to glucose and mannitol. As co mmercial sugar is cheaper than sucrose it was selected as carbon source for PHB production, that being found to be maximum at I % concentration. Inorg anic nitrogen sources seemed to have no stimulatory effect on the productio n of PHB. However, ammonium acetate (15 mmol/L) was found to be best for PH B production. Peptone (0.2 %) gave a better yield of PHB under both growth conditions. Using all optimized conditions, PHB production was studied in t en selected strains. Two of them were found to be best PHB producers under both growth conditions, one producing 621 and 740 mug/g dry mass under subm erged cultivation and under stationary cultivation, respectively, while the second one produced 589 and 733 mug/g.