Biosynthesis of Poly--hydroxybutyrate as a Biodegradable Polymer

Poly-β-hydroxybutyrate (PHB) is a biodegradable polymer which is regarded as a new environmentally compatible material. A wide variety of micro-organisms accumulate poly-β-hydroxybutyrate within cells as an intracellular storage material of carbon and energy. In this study, PHB was synthesized by Ralstonia eutropha (formerly Alcaligenes eutrophus) in a defined medium consisted of fructose as a sole carbon source. The effect of four process variables was studied to optimize the biosynthesis of PHB in bench scale. The results showed that the fresh inoculum at the mid-exponential phase lead to more growth during fermentation. The optimum shaking rate and temperature were 250 rpm and 25°C, respectively. The high concentration of fructose inhibited the growth, so it was optimized at 15 gL-1. Under these conditions, PHB was accumulated as inclusion bodies so that 70% of the dry cell weight of Ralstonia eutropha was composed of PHB. The yield coefficients of biomass and product were 0.3 and 0.21 g.g-1, respectively.