Fatemeh Davoodi-Dehaghani - Department of Biology, Faculty of Basic Sciences, Central Tehran Branch, Islamic Azad University, Tehran, Iran
Mohammad Barshan-tashnizi - Department of Life Science Engineering, Faculty of New Sciences and Technologies, University of Tehran, Tehran, Iran

Background and Aim : The world is moving towards zero-sulfur fossil fuels. Among the different technologies to remove sulfur from petroleum, biodesulfurization (BDS) is an effective approach. It's based on the sulfur metabolism in some of the living systems including archaeal, bacterial, and fungal members. BDS occurs at ambient temperature and pressure with high selectivity, without undesirable side-products. It significantly reduces sulfur content in a cost-effective manner. In recent years, Rhodococcus erythropolis SHT۸۷ has been identified and introduced as a bacterium capable of desulfurizing resistant sulfur-containing compounds including dibenzothiophene (DBT) in fossil fuels.Methods : Rhodococcus erythropolis SHT۸۷ was cultivated in a minimal culture medium (BMV) including the phosphate buffer solution, the metals solution, and the vitamins solution. BMV medium had glycerol (۵ g/L) and DBT as the only source of carbon and the only source of sulfur. In the middle of the logarithmic phase, the SHT۸۷ cells were precipitated by centrifuge and were eluted by the phosphate buffer solution. Then, according to the determined relation between optical absorbance in ۶۶۰ nm and dry cell weight, the prepared resting cells of SHT۸۷ were added to the biphasic system (mixture of ۲:۱ n-tetradecane/water) up to ۱۰ gDCW/L. DBT concentration was ۳ mM and the process was run in a ۳L bioreactor (۳۰ oC, pH ۶, ۴۰۰ rpm, and ۱ vvm). Results : The specific desulfurization activity in the first two hours was measured by HPLC based on ۲-HBP production. It was ۱.۲ micromole ۲-HBP/gDCW.min.Conclusion : This study demonstrates that R. erythropolis SHT۸۷ has desired specific activity of DBT desulfurization in the stirred tank bioreactor. Therefore SHT۸۷ can be used for improving fossil fuels.

Rhodococcus erythropolis SHT۸۷; stirred tank bioreactor; fossil fuels.