Effect of co-substrate on production of poly-β- hydroxybutyrate (PHB) and copolymer PHBV from newly identified mutant Rhodobacter sphaeroides U7 cultivated under aerobic-dark condition

Abstract

Photosynthetic bacterial mutant strain U7 was identified using both classical and molecular (16S rDNA) techniques to be Rhodobacter sphaeroides. The glutamate-acetate (GA) medium containing sodium acetate and sodium glutamate as carbon and nitrogen sources was used for production of poly-β-hydroxybutyrate (PHB) from R. sphaeroides U7 cultivated under aerobic-dark condition (200 rpm) at 37oC. Effect of auxiliary carbon sources (propionate and valerate) and concentrations (molar ratio of 40/0, 40/20, 40/40 and 40/80) on copolymer production were studied. Both combinations of acetate with valerate and acetate with propionate were found to induce the accumulation of poly-β-hydroxybutyrate-co-β-hydroxyvalerate (PHBV) within the cell. Acetate with propionate in the molar ratio of 40/40 gave the highest poly-β-hydroxyalkanoates (PHA) content (77.68%), followed by acetate with valerate at the same molar ratio (77.42%). Although their polymer contents were similar, the presence of 40 mM valerate gave more than 4 times higher hydroxyvalerate (HV) fraction (84.77%) than in the presence of 40 mM propionate (19.12% HV fraction)