Improvement of the PHB Production Process by Bacillus Megaterium MNSH1-9K-1 in a Medium Prepared from Orange-peel Residues

Abstract

Polyhydroxybutyrate (PHB) is a thermoplastic biopolymer synthesized by a wide range of microorganisms, such as Bacillus cereus ARY73, Klebsiella pneumoniae E22, and Pseudomonas putida. Although PHB is a feasible option to substitute conventional plastics for specific purposes, this substitution has not been satisfactory due to its high production cost mainly due to the materials used for bacterial growth and the low yields obtained. Bacillus members are known for their ability to produce PHB, as they can accumulate this biopolymer in up to 80% of their weight, specifically under stressful growth conditions. B. megaterium strain MNSH1-9K-1 can produce up to twice as much PHB compared to other high-producing strains reported to date in a low-cost medium prepared from orange peels, and it was previously shown that this production can be enhanced by modifying some growth conditions using a presence/absence experimental design. Then, to identify the quantities of specific factors that can improve this PHB production by MNSH1-9K-1, different experimental scenarios were evaluated in the present work using the low-cost medium, including carbon and nitrogen concentrations, temperature, and aeration. PHB production was improved up to three times with a C/N ratio of 16:1. In addition, the significance of the evaluated variables for PHB production was determined by a response surface regression model. Due to the high production yield obtained with the use of a low-cost medium, the PHB production process using B. megaterium MNSH1-9K-1 may be a promising alternative to further explore its scale-up potential.