Optimization of Polyhydroxyalkanoates Production from Thermus thermophilus HB8 Using Response Surface Methodology

The thermophilic bacterium Thermus thermophilus HB8 was used for the overproduction of polyhydroxyalkanoates (PHAs) using a mathematical approach for the first time for optimization of process variables. In addition, the combined effect of nitrogen and phosphate concentrations on PHAs production was also investigated. A five-level-three-factor central composite rotary design was employed in combination with response surface methodology (RSM) to optimize the process variables for the production of PHAs in Thermus thrermophilus HB8. The three independent variables studied in the work were cultivation time, C/N ratio and phosphate concentration. Two second-order polynomial equations were obtained for biomass and PHA production by multiple regression analysis using RSM. The statistical analyses of the results showed that all the three variables had significant impact both on the cell growth and polymer accumulation. The model predicted a maximum PHA production of 0.47 g/L which represents the 42 % of dry cell weight (DCW) after 55 h of cultivation and with on setting the C/N ratio at 9:1 g/g and phosphate concentration at 20 mM. Verification of the predicted value resulted into a PHA production of 0.44 g/L (40.36 % of DCW).