Optimization of media composition for enhancing carbazole degradation by Pseudomonas aeruginosa RS1

Abstract

Plackett-Burman design (PBD), steepest ascent method (SAM) and central composite design (CCD) using response surface methodology (RSM) were applied to explore the effects of sixteen media components on carbazole degradation by Pseudomonas aeruginosa RS1. Carbazole acclimatized P. aeruginosa RS1 was grown on 100 mg/L carbazole provided as sole substrate in 50 mL mineral media and residual carbazole was quantified after 8 days. PBD revealed media components, MnCl2·4H2O (L), NiCl2·6H2O (J) and CaCl2·2H2O (P) as the most significant. SAM indicated that increasing concentration of MnCl2·4H2O (L) and decreasing concentrations of NiCl2·6H2O (J) and CaCl2·2H2O (P) from their center point levels increased carbazole degradation. CCD using RSM indicated the optimum concentrations of L, J and P as 57.04, 0.046 and 15 mg/L, respectively. Carbazole degradation in the optimized media (67 ± 2.7%) closely matched the theoretically predicted value (67%) and was much higher than that in the unoptimized media (38 ± 1.2%). Culture growth was significantly enhanced in the optimized media and disc diffusion studies confirmed growth inhibitory effect of J and P at concentration beyond the optimum values identified. Some accumulation of metabolites was also observed over the log growth phase. Increase in L caused enhanced accumulation of metabolites at the end of log phase, thus, it possibly enhanced carbazole degradation by increasing the activity of upper pathway enzymes having Mn as a cofactor.