Isolation and Characterization of Poly-(R)-3-hydroxybutyrate Produced by Bacillus thuringiensis TH-01

Abstract

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%.