Nutrient optimization for production of polyhydroxybutyrate from halotolerant photosynthetic bacteria cultivated under aerobic-dark condition

three halotolerant bacterial strains; rhodobacter sphaeroides es16 (the wild type) and the two mutant strains of r. sphaeroides es16, namely n20 and u7, were cultivated in glutamate-malate (gm) medium and screened for production of polyhydroxybutyrate (phb). the mutant strains n20 and u7 were found to accumulate phb (53.9 and 42.0% of dcw, respectively) 3.6 and 2.8 times higher than the wild type strain (19.5% of dcw), respectively. r. sphaeroides n20 were selected for studies on the effects of nutrient and environmental conditions on phb accumulation. the optimal condition was 4 g/l acetate, 0.02 g/l (nh4)2so4, c/n ratio of 6:1, 1.0 g/l k2hpo4, 1.0 g/l kh2po4 and 3% nacl with initial ph at 7.0. under this optimal condition, the maximum phb accumulation increased from 53.9% to 88% of dcw and 9.11 ± 0.08 g/l biomass, 8.02 ± 0.10 g/l phb concentration were achieved after 60 hrs cultivation at 37oc. these results are the highest values ever obtained from photosynthetic bacteria reported so far.