Sahar Keskes1, Wafa Jallouli2, Imen Ben Atitallah3, Fatma Driss1, Emna Sahli4, Mohamed Chamkha5, Slim Tounsi1. 1. Laboratory of Biopesticides, Centre of Biotechnology of Sfax, Sfax University, P.O. Box '1177', 3018, Sfax, Tunisia. 2. Laboratory of Biopesticides, Centre of Biotechnology of Sfax, Sfax University, P.O. Box '1177', 3018, Sfax, Tunisia. jallouliwafa2@yahoo.fr. 3. Laboratory of Enzyme Engineering and Microbiology, National School of Engineering of Sfax (ENIS), Sfax University, BP 1173, 3038, Sfax, Tunisia. 4. Analysis Laboratory, Centre of Biotechnology of Sfax, Sfax University, P.O. Box '1177', 3018, Sfax, Tunisia. 5. Laboratory of Environmental Bioprocesses, Centre of Biotechnology of Sfax, Sfax University, P.O. Box '1177', 3018, Sfax, Tunisia.
Abstract
This study investigates the optimization of the culture conditions for enhancing Photorhabdus temperata biopesticide production using wastewater (WS4) as a raw material. Box-Behnken design (BBD) was used to evaluate the effects of carbon to nitrogen ratio (C/N), sodium chloride concentration and inoculum size on P. temperata biomass production and insecticidal activity. For an enhanced biopesticide production, the optimum operating conditions were as follows: inoculum size = 4%; C/N ratio = 12.5 and [NaCl] = 4 g/L for two responses. 1.95 and 2.75 fold improvements in oral toxicity and biomass production were respectively obtained in the cost-effective medium developed in this study (WS4 I) using the three variables at their optimal values. Under the optimized conditions, WS4 I-grown cells exhibited higher membrane integrity according to flow cytometry analysis since dead cells presented only 9.2% compared to 29.2% in WS4. From batch fermentations carried out in WS4 I and WS4, P. temperata kinetic parameters in terms of biomass production and substrate consumption rates were modeled. The obtained results showed that the maximum specific growth rate in WS4 I was of 0.43 h-1 while that obtained in WS4 was of 0.14 h-1. In addition, the efficiency of P. temperata to metabolize organic carbon was enhanced by optimizing the culture conditions. It reached 72.66% instead of 46.18% in the control fermentation after 10 h of incubation. Under the optimized conditions, P. temperata cells showed the highest specific consumption rate resulting in a toxin synthesis improvement.
This study investigates the optimization of the culture conditions for enhancing Photorhabdus temperata biopesticide production using wasten class="Chemical">water (WS4) as a raw material. Box-Behnken design (BBD) was used to evaluate the effects of carbon to nitrogen ratio (C/N), sodium chloride concentration and inoculum size on P. temperata biomass production and insecticidal activity. For an enhanced biopesticide production, the optimum operating conditions were as follows: inoculum size = 4%; C/N ratio = 12.5 and [NaCl] = 4 g/L for two responses. 1.95 and 2.75 fold improvements in oral toxicity and biomass production were respectively obtained in the cost-effective medium developed in this study (WS4 I) using the three variables at their optimal values. Under the optimized conditions, WS4 I-grown cells exhibited higher membrane integrity according to flow cytometry analysis since dead cells presented only 9.2% compared to 29.2% in WS4. From batch fermentations carried out in WS4 I and WS4, P. temperata kinetic parameters in terms of biomass production and substrate consumption rates were modeled. The obtained results showed that the maximum specific growth rate in WS4 I was of 0.43 h-1 while that obtained in WS4 was of 0.14 h-1. In addition, the efficiency of P. temperata to metabolize organic carbon was enhanced by optimizing the culture conditions. It reached 72.66% instead of 46.18% in the control fermentation after 10 h of incubation. Under the optimized conditions, P. temperata cells showed the highest specific consumption rate resulting in a toxin synthesis improvement.
Authors: Nicholas Waterfield; Shizuo George Kamita; Bruce D Hammock; Richard ffrench-Constant Journal: FEMS Microbiol Lett Date: 2005-04-01 Impact factor: 2.742