Poly-(R)-3-hydroxybutyrate (PHB) is a biopolymer that can be synthesized by several microorganisms such as bacteria, yeast, and fungi as secondary metabolites. PHB is produced by bacteria in a medium containing a limited amount of key nutrients such as nitrogen, phosphorus, and magnesium but rich in carbon sources. PHB is a biodegradable plastic that has many applications in the medical and industrial fields. This study aimed to isolate and characterize a biopolymer produced by a bacterium strain isolated from a termite nest in India that was identified by 16S rRNA method as Bacillus thuringiensis TH-01. The biopolymer was produced by growing the bacteria in a high medium overnight at 37 °C in a shaking incubator at 150 rpm, and the resulting biopolymer was extracted with a mixture of chloroform–NaOCl (1:1). The efficiency of biopolymer production was about 10.545% ± 26.125%. Fourier transform infrared analysis gave prominent absorption peaks at 3400 cm−1 (stretching of O–H), 2900 cm−1 (stretching of C–H), 1700 cm−1 (stretching of C=O), 1280 cm−1 (symmetric deformation of C–H), and 1050 cm−1 (stretching of C−O), confirming that the biopolymer is PHB. The thermal stability of PHB granules as was determined by thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) showed that the decomposition temperature and of the polymer were 271.6–310.0 °C and 7.48 J/g respectively, and its crystallinity was about 5.12%.

Poly-(R)-3-hydroxybutyrate (PHB) is a bioplastic derivative of polyhydroxyalkanoate (PHA) which can be synthesized by bacteria under certain growth conditions. Previous study has reported a new strain of Bacillus thuringiensis TH-01 isolated from thermite, which found to accumulate PHB. This research aimed to clone PHB biosynthesis genes from B. thuringiensis TH-01 and study its expression as well as predict the tertiary structure of the enzymes. The clone of phaA gene, which encodes PhaA, was obtained as 1182 bp. On the other hand, 2546 bp clone of phaRBC gene cluster was obtained to consist of 744 bp phaB, 1086 bp phaC, and 483 bp phaR, encoding respective PhaB, PhaC, and PhaR proteins. In silico analysis indicated that PhaA, PhaB, PhaC, and PhaR, revealed to have 393, 247, 361, and 160 amino acid, respectively. The predicted model of PhaA, PhaB, and PhaC showed dominant structure of α/β folding motif, while PhaR was dominated by a helix-loop-helix motif. The catalytic residues of PhaA were Cys88, His349, and Cys379, whereas the catalytic residues of PhaB were Ser142, Tyr155, and Lys159. These catalytic residues were identical to those residues obtained in other PHB biosynthetic enzymes reported elsewhere, confirming that our clones were of PHB biosynthetic genes.