Response surface optimization of experimental conditions for carbamazepine biodegradation by Streptomyces MIUG 4.89

Carbamazepine an iminostilbene derivative compound with a tricyclic structure is one of the most widely prescribed drugs for the treatment of epilepsy. It is hardly or not degraded during the conventional technology used in wastewater treatment plants (WWTPs) (up to 7%) and many studies have found it ubiquitous in various environmental matrices in concentrations typically ranging from μg L(-1) to ng L(-1). Streptomyces MIUG 4.89 was previously studied for its ability in carbamazepine biodegradation (up to 14%) during cultivation in submerged system under aerobic conditions at an initial CBZ concentration of 0.2 mg L(-1). The influence of some factors (independent variables) upon biodegradation potential was examined by Plackett-Burman analysis. Central composite design of experiments (CCD) and response surface methodology (RSM) were used to get more information about the significant effects and their interactions of the five parameters selected upon their biodegradation potential in order to increase the elimination yield of this drug from a liquid medium. The investigated ranges of the independent variables were: 1.0-3.0 g L(-1) yeast extract, 3.0-10.0 g L(-1) glucose, 4.0-10.0% (v/v) inoculation level, pH 5.0-7.0 and 50-250 mL of medium at a constant initial concentration of carbamazepine (CBZ) of 0.2 mg L(-1). The response surface analysis results showed that the capacity of the selected strain Streptomyces MIUG 4.89 to degrade carbamazepine was high in submerged cultivation system by cultivation in a liquid medium containing 6.5 g L(-1) glucose and 2 g L(-1) yeast extract, inoculated at 7% (v/v) and cultivated at pH 6.0, during 7 days of incubation at 25 °C and 150 rpm. Under these culture conditions the achieved experimental CBZ biotransformation yield was 30%.