Fermentative production of polyhydroxybutyrate (PHB) from sucrose based resources

Abstract

Polyhydroxybutyrate (PHB), a type of biodegradable plastic, which has attracted significant interest as a replacement for petroleum-derived plastics because of its degradability, sustainability and some properties similar to conventional plastics, is still not being produced commercially for consumer products because of its high cost. Its cost of production is 5-10 times higher as compared to the conventional plastics. One the major factor leading to this high cost of production is cost of the substrate used for production. Hence, this study focused on the production of PHB from a cheap substrate - table sugar which is a sucrose based renewable source. The microbial strain used was Cupriavidus necator (MTCC 1472). Optimisation of media components was done for PHB production in shake flask by applying Plackett-Burman design and Response Surface Methodology. Using the optimised media scale-up of PHB production from shake flask to fermenter was carried out. In batch fermentation maximum biomass and PHB obtained were 4.724g/L and 2.824 g/L respectively with PHB productivity of 0.072g/Lh. Fed-batch fermentation studies were then done at different flow rates to enhance PHB production. At flow rate of 70 mL/h, 2.88-fold increase in productivity and at 30 mL/h, 2.57-fold increase in productivity was achieved as compared to batch cultivation. Extraction efficiencies of different methods were also investigated and surfactant hypochlorite digestion method was found to give maximum PHB extract per gram biomass.