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 OD 600 = 0.69 and 64.11%, respectively, which is very close to the predicted cell growth and toluene degradation of OD 600 = 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.

Hydrocarbons pollution is a most important environmental and healthanxiety . Using free and immobilized bacteria could be a suitable attitude to find a proper bioaugmentation agent. A toluene degrading bacterium was isolated from oil-contaminated environs (located in Bandar-Anzali, Guilan, Iran). The strain was molecularly identified as Staphylococcus gallinarum ATHH41 (Accession number: KX344723) by partial sequencing of 16SrDNA gene. The response surface methodology (RSM) was expended for biodegradation of the toluene by ATHH41. The central composite design (CCD) was utilized to optimize pH, temperature, and toluene concentration by ATHH41. In accordance with the optimization purpose of the Design-Expert software, the optimum circumstances of toluene degradation were obtained when pH, temperature and toluene concentration were adjusted to 7.68, 31.73°C and 630.04 mg.l-1, respectively. Multi-walled carbon nanotubes (MWCNTs) were used to immobilize the strain. Infrared spectroscopy and scanning electron microscopy showed that the cells adhered to the MWCNT surface and developed a biofilm. Results reveal that free cells were able to degrade 68.01% of the toluene as the sole carbon and energy source within 24 h under optimized conditions. The immobilized cells reached 95.68%.