An extensive screening program was previously done to isolate a promising bacterial isolate Azomonas macrocytogenes isolate P173 capable of polyhydroxybutyrate (PHB) production. It produced 24% PHB per dry weight after 48 h. In this study, several experiments were designed to optimize the composition of the culture medium and environmental factors for maximizing PHB production by the respective isolate. Results show that 60% aeration, incubation temperature 37°C and an initial pH 7.5 were optimum for PHB production. A modified culture medium for PHB production was designed containing 0.7% glucose and 100 mg/L potassium nitrate as a carbon and nitrogen sources, respectively. Using this modified medium together with optimum environmental conditions, PHB production was increased from 24 to 42% per dry weight after 24 h of incubation rather than 48 h. Acriflavin-induced mutation resulted in one variant (173A2) which produced 47% PHB per dry weight after 24 h of incubation using the same modified culture medium except for glycerol 1.5% as carbon source.
Key words: Azomonas macrocytogenes, poly-β-hydroxybutyrate, optimization of microbial bioplastics bioplastic.
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