Production of Polyhydroxyalkanoates by Rhodopseudomonas palustris: Effect of Some Waste Materials and Toxic Substances

Abstract

The ability of the phototrophic purple non sulfur bacterium, Rhodopseudomonas palustris SP5212 to grow and produce bioplastics, polyhydroxyalkanoates (PHAs) utilizing industrial and domestic wastes have been assessed during the present study. Growth and PHA accumulation by the isolate under oneand two-step cultivation in phototrophic, microaerophilic conditions have been determined. Municipal waste and pond sludge supplemented with acetate medium at 1:1 ratio favoured growth and synthesized PHAs accounting 16 and 19 % of cell dry weight (CDW) respectively. In two-step cultivation, the accumulated copolymer, poly (3-hydroxybutyrate-co-3- hydroxyvalerate) [P(3HB-co-3HV)] increased up to 25 and 37 % CDW with 37 and 52 mol % of 3-hydroxyvaleric acid (3HV) monomers. The isolate tolerated heavy metals like Co(II) and Ni(II) and several aliphatic and aromatic compounds. While the aliphatic compounds favoured co-polymer synthesis, aromatic compounds led to the accumulation of lower amount of poly (3-hydroxybutyric acid) [P(3HB)] only. It was apparent that the bacterium, R. palustris could be effectively applied in utilizing domestic and industrial wastes simultaneously with the production of biodegradable polymers of commercial importance in a cost-effective manner. Moreover, successful implementation of the metabolic potential of the phototrophic bacterium will help in waste management, reduction of pollution in the environment along with production of eco-friendly PHA plastics.