Application of weighted response surface methodology for enhanced poly (3-hydroxybutyrate) production by endophytic bacillus cereus RCL 02

Abstract

Application of statistical models in developing strategies for process optimization and enhanced product yield is well established. The present study is focused to enhance poly (3-hydroxybutyrate) [P(3HB)] production by Bacillus cereus RCL 02, a leaf endophyte of oleaginous plant Ricinus communis L. using weighted response surface methodology (WRSM). The most influencing process variables for growth and bio-polyester accumulation were initially selected through Plackett-Burman (PB) designed experiments. Further, WRSM was applied to navigate the experimental data obtained in accordance with the central composite design (CCD). Interaction of three independent variables viz. carbon source (glucose), nitrogen source (yeast extract) and initial pH of the medium exerted most significant impact on biomass formation as well as P(3HB) production. A second order polynomial equation obtained from multiple regression analysis and the interaction studies from surface plots helped to determine the optimum concentrations of glucose (25g/L), yeast extract (4g/L) and initial pH (7.6). Validation of this statistical model was executed using point prediction tool of WRSM where-from the optimum values of all three significant variables were employed and experiments were conducted. Under such optimized conditions the endophytic isolate produced 8.07g/L of P(3HB), which was very close to the predicted value (7.80g/L) and thereby validated the model. Finally, the identity of the intracellularly accumulated bio-polyester of B. cereus RCL 02 was confirmed by proton nuclear magnetic resonance (1H NMR) spectroscopic analysis.