Improved poly(3-hydroxybutyrate) production by new strain of Bacillus paramycoides AAR-6

Improving polyhydroxyalkanoate (PHA) production process for maximum yield at low cost is particularly important for accelerating the replacement of non-degradable petroleum polymer with biodegradable biopolymer. Bacillus paramycoides is a significance biocatalyst capable of producing valuable macromolecules of industrial importance. The study investigated the effect of physiological parameters, such as pH, nitrogen types, and incubation flux on growth and PHA production in new strain of Bacillus paramycoides AAR-6. Optimizing the individual and combined nitrogen sources (NH₄Cl, (NH₄)₂SO₄, NH₄NO₃, and yeast extract), and three-step fermentation process using Taguchi design of experiment, where the dynamics of the carbon %, nitrogen %, feeding broth pH and incubation period of each fed-batch for maximum PHA yield, were also carried out. The produced PHA was subsequently identified and characterized for potential industrial applications. Initial assay showed that pH 9.0 stimulated 0.142 g L^-1 dry weight of PHA, while the acidic media (pH 5.0) and neutral (pH 7.0) yielded PHA of 0.012 g L^-1 and 0.068 g L^-1 respectively. A combination of nitrogen sources (NH₄NO₃ and yeast extract) in the ratio 1:1 stabilized the culture pH condition between 6.50 and 6.96, enhanced the bacterium's kinetic growth and led to a PHA yield of 0.620 g L^-1, constituting 50 % of the dry biomass weight. The optimal 3-fed batch fermentation conditions improved the biomass and PHA weight to 2.2 g L^-1 and 1.12 g L^-1, respectively. The biopolymer, identified as poly(3-hydroxybutyrate), is semi-crystalline in nature with a very low crystallinity level (11 %), thermal degradation at 261.3 °C and thermostable up to 130.9 °C. This study introduces a novel, sustainable bioprocess that integrates physiological stability and nutritional balance to enable cost-effective PHA synthesis using a newly isolated bacterial strain.