Recovery and molecular characterization of poly-β-hydoxybutyrate polymer by Bacillus cereus isolate P83

Abstract

Production of polyhydroxyalkanoates by Bacillus cereus isolate P83 was carried out in a 14L laboratory fermentor using mineral salt medium containing 0.7% corn oil and 0.1 g/L ammonium chloride as carbon and nitrogen sources, respectively at 28°C, 200 rpm, 2 vvm and 7.2 pH. The maximum level of polyhydroxyalkanoates (53% per dry weight) was achieved after 24 hours of incubation. Different methods (Digestion by sodium hypochlorite, dispersion of chloroform and hypochlorite, mechanical dispersion and chloroform extraction) were used for polymer recovery. According to the obtained results, the highest molecular weight of polymer (2.15*104 g/mole) and lowest polydispersity (1.15) were achieved using chloroform extraction method. The results of the characterization techniques, IR and 1H-NMR spectroscopy, showed polyhydroxybutyrate identity. Analysis of PHA synthase and PhaR subunit PCR products indicated class IV PHA synthase with enzymatic and specific activity (measured by DTNB assay) of 195U and 1500U/mg, respectively. In conclusion, Bacillus cereus isolate P83 is a candidate for commercial production of PHB polymer with high growth rate and promising polyhydroxybutyrate production level. The produced polymer is characterized by comparable molecular weight of polymer with low polydispersity value.