Optimizing toluene degradation by bacterial strain isolated from oil-polluted soils

Abstract

The presence of toxic compounds like toluene has caused extensive contamination in oil-contaminated environments. Using bacteria to degrade monoaromatic compounds could be a good approach to finding a suitable bioaugmentation agent. In this study on toluene, degrading bacterial species were isolated from oil-contaminated environments (located in Bandar-Anzali, Guilan, Iran). The strain has been molecularly identified as Bacillus cereus ATHH39 (Accession number: KX344721) by partial sequencing of the 16S rDNA gene. Response surface methodology (RSM) was used for biodegradation of toluene by ATHH39 by implementing the central composite design (CCD). The central composite design (CCD) was applied to optimize and investigate pH, temperature, and toluene concentrations and their interactions for enhancing cell growth and toluene degradation by ATHH39 under in vitro conditions. The variables (pH, temperature, and toluene concentrations) with the highest significant impacts on growth and toluene degradation were selected. According to the prediction and optimization function of the design expert software, the optimum conditions of cell growth and toluene degradation were found. When pH, temperature, and toluene concentration were adjusted to 6.72, 33.16ºC and 824.15 mg/l, respectively, cell growth and toluene degradation reached OD600 = 0.69 and 64.11%, respectively, which is very close to the predicted cell growth and toluene degradation of OD600 = 0.71 and 65.85%, indicating that the response surface methodology optimization of process parameters for cell growth and toluene degradation is reliable. Based on the results, the ATHH39 strain was introduced as a useful microorganism with the potential for bioremediation of wastewater containing toluene.