Development of a Cost-effective Medium for Photorhabdus Temperata Bioinsecticide Production From Wastewater and Exploration of Performance Kinetic

Abstract This study investigates the optimization of culture conditions for enhancing Photorhabdus temperata biopesticide production using wastewater (WS4) as a raw material. Box-Behnken design (BBD) was used to evaluate the effect of carbon to nitrogen ratio (C/N), NaCl concentration and inoculum size on Photorhabdus temperata biomass production and insecticidal activity. Modelling results suggest that the selected variables had contributed significantly to the responses. For enhanced biopesticide production the optimum operation conditions were as follow: inoculum size=4 %; C/N ratio=12.5 and sodium chloride concentration= 4 g/L for two responses. 1.95 and 2.75 folds improvement in oral toxicity and biomass production, respectively, were obtained when using the three variables at their optimum values. From batch fermentations carried out in the cost-effective medium developed in this study (WS4 I) and WS4 used as control, P. temperata kinetic parameters in term of biomass production and substrate consumption were modeled. The obtained results showed that the maximum specific growth rate was of 0.38 h-1 compared to 0.16 h-1 obtained in WS4. In addition, the efficiency of P. temperata to metabolize organic carbon was enhanced by optimizing culture conditions reaching 70 % instead of 47.2 % in the control fermentation. Under the optimized conditions, P. temperata cells showed higher specific consumption rate resulting in P. temperata toxin synthesis improvement.