Statistical optimization studies for polyhydroxybutyrate (PHB) production by novel Bacillus subtilis using agricultural and industrial wastes

Abstract

Substituting petroleum-derived polymers with biodegradable and biocompatible polyhydroxybutyrate (PHB) is a challenge to sustain the environmental system. This study intends to optimize the cultural conditions for PHB production by nonpathogenic Bacillus subtilis isolated from Jatropha field. Various agricultural and industrial wastes such as corn bran, corncob, wheat bran, rice bran, dairy waste, and sugarcane molasses were utilized for PHB production. Among these wastes, rice bran was the best carbon source for PHB production (0.31 g/l) with 30.4% of the dry cell weight (DCW). Cultural parameters influencing PHB production were studied employing Plackett–Burman and Box–Behnken designs. Accordingly, pH, incubation time, and inoculum size were found to be the most influential factors on PHB production. Using optimized conditions, sixfold augment in PHB content (0.81 g/l, 62.6% DCW) was attained using rice bran. PHBs obtained from glucose and rice bran were characterized using 1H NMR, FT-IR, TGA, and DSC analysis. Structures of PHBs were comparable, whereas the findings of thermal studies revealed that rice bran-derived PHB showed higher thermal stability with lower melting temperature than glucose-derived PHB. These results substantiate the potential use of this safe isolate utilizing inexpensive substrates for PHB production that could be adopted in medical applications.