Optimization of polyhydroxybutyrate (PHB) production by Priestia megaterium ASL11 and glycerol and thermoplastic properties of PHB-based films

Abstract

The production of polyhydroxybutyrate (PHB) by Priestia megaterium ASL11 was elucidated with various carbon sources. The optimized conditions for PHB production were as follows: C/N ratio of 6.99; mixture of 3% (v/v) glycerol, 0.079% (w/v) malt extract and 0.35% (w/v) sodium ammonium phosphate; initial medium pH of 8.0; and incubation time of 120 h. These optimal conditions increased the PHB concentration (g/L), PHB yield, and PHB content produced by ASL11 from 0.32, 0.13, and 15.8% (using glucose) to 0.92, 0.78 and 49.6% (using glycerol), accounting for 2.9-, 6.0- and 3.1-fold increases, respectively. FTIR analysis of the ASL11-PHB film revealed carbonyl (1720 cm−1) and alkane (1453–1379 cm−1) groups similar to those of standard PHB, and GC/MS analysis confirmed that the characteristics of PHB obtained with ASL11 were consistent with those of standard PHB. The ASL11-PHB film was resistant to heat (90–175 °C) and pH values from 5 to 10 and had a melting temperature of 165.1 °C, indicating typical thermobioplastic properties. The ASL11-PHB film could be completely dissolved in sulfuric acid, which is less toxic than chloroform. The mechanical properties of the ASL11-PHB film showed a low Young's modulus with an elongation at break of 5.27%, indicating brittle behavior with low mechanical strength. Thus, the ASL11-PHB film should be blended with other materials to reinforce the film strength and reduce its brittleness for future applications. Moreover, the studies of PHB production under optimal condition by ASL11 needs to be scaled up from the laboratory scale to the pilot scale.