Optimization for Polyhydroxyalkanoate Production from Various Carbon Sources and C:N Ratios by Bacillus sp. under Nitrogen Limitation

The global reliance on petroleum-based plastics has intensified the demand for biodegradable alternatives such as polyhydroxyalkanoates (PHAs). In this study, PHA production by Bacillus sp. was investigated under nitrogen-limited conditions with glucose, fructose, and sucrose as carbon sources at varying C:N ratios (19:1, 38:1, 76:1). Batch experiments were performed to evaluate biomass growth and intracellular polymer accumulation. Glucose proved to be the most effective substrate, supporting a maximum PHA content of 82.9% of cell dry weight at a C:N ratio of 38:1 after 48 h. Fructose yielded moderate accumulation (54%) but showed degradation at extended incubation, while sucrose supported only limited storage (35%). Excessive nitrogen limitation reduced both biomass and polymer yields, whereas moderate limitation optimized accumulation. These findings highlight the decisive role of nutrient balance and substrate choice in PHA biosynthesis and demonstrate the potential of Bacillus sp. for sustainable bioplastic production.