The extensive use of conventional non-biodegradable plastics has resulted in severe environmental pollution and long-term ecological imbalance, making plastic waste one of the most serious global environmental challenges of the present century. In response to this growing concern, polyhydroxybutyrate (PHB) has emerged as a promising eco-friendly alternative due to its biodegradable, non-toxic, and biocompatible nature, along with physical properties comparable to petroleum-based plastics. PHB is a naturally occurring biopolymer synthesized by various microorganisms and undergoes rapid degradation in natural environments, thereby reducing its environmental impact. In the present study, soil samples were collected from the rhizosphere of mung bean (Vigna radiata), an ecological niche known for its high diversity of PHB-producing bacteria. Bacterial strains were isolated and screened for PHB production, and the most efficient PHB-producing isolate was identified as a Bacillus species for further growth and production studies. The intracellular accumulation of PHB was initially confirmed using Sudan Black staining, which revealed distinct dark granules within the bacterial cells. Based on PHB yield, the isolates were classified into high, medium, and low producers, and representative strains from each group were selected for biochemical characterization and optimization of culture conditions, including carbon and nitrogen sources, C/N ratio, pH, temperature, and incubation period. Maximum PHB production was achieved using glucose as the carbon source, ammonium sulphate (1.0 g/L) as the nitrogen source, with a C/N ratio of 20:1, at pH 7.0 and an incubation temperature of 30°C for 48 hours. Several isolates demonstrated significantly enhanced PHB accumulation under these optimized conditions, indicating strong potential for industrial applications. The extracted polymer was further charac-terized and confirmed by FT-IR spectroscopy, which revealed characteristic absorption peaks corresponding to functional groups such as C=O stretching, CH2 groups, and ester C–O bonds, thereby confirming the identity of PHB.

Polyhydroxybutyrate (PHB), Bioplastic, Rhizosphere Soil, Bacillus Species, Biodegradable Polymer, PHB Optimisation, FT-IR Characterization