Hadieh Roohian - MSc. Student, Biotechnology Group, Department of Chemical Engineering, Faculty of Engineering, Tarbiat Modares University.
Ebrahim Vasheghani Farahani - Professor of Chemical Engineering, Biotechnology Group, Department of Chemical Engineering, Faculty of Engineering, Tarbiat Modares University.
Seyed abbas Shojaosadati - Professor of Chemical Engineering, Biotechnology Group, Department of Chemical Engineering, Faculty of Engineering, Tarbiat Modares University.

Polyhydroxybutyrate is a biodegradable polymer, which is regarded as an environmentally compatible material. Wide varieties of microorganisms accumulate polyhydroxybutyrate intracellularly as storage of carbon and energy. One way to increase the PHB content is to increase intracellular NADPH/NADP+ ratio in order to activate PHB production pathway. In the present study, PHB was synthesized by Watresia eutropha (formerly Ralstonia eutropha) in a defined medium and the effect of redox potential on the enhancement of PHB production was investigated. Based on the growth curve, the redox potential was exerted to the growth media at two different times, one at the beginning of the exponential phase and another at the beginning of the stationary phase. The best results for PHB accumulation were obtained from first condition at the cathode. According to these results, PHB accumulation was 45.7% of the dry cell weight, which increased by 30.2% compared to blank. It was observed that in the first condition at the cathode, PHB production pathway was more active and cell growth was partially inhibited during exponential phase. As by increasing redox potential, PHB concentration and PHB content decreased, the appropriate magnitude of redox potential for increasing intracellular NADPH/NADP+ ratio and therefore PHB content was 0.5V.

Polyhydroxybutyrate, Watresia eutropha, redox potential, NADPH, fructose