BACKGROUND: To meet stringent emission standards stipulated by regulatory agencies, the oil industry is required to bring down the sulfur content in fuels. As some compounds cannot be desulfurized by existing desulfurizing processes (such as hydrodesulfurization, HDS) biodesulfurization has become an interesting topic for researchers. Most of the isolated biodesulfurizing microorganisms are capable of desulfurization of refined products whose predominant sulfur species are dibenzothiophenes so biocatalyst development is still needed to desulfurize the spectrum of sulfur-bearing compounds present in whole crude. RESULTS: The first desulfurizing bacterium active at 60 degrees C has been isolated, which reduces DBT concentration from 2 mmol L-1 to 0.1 mmol L-1 after 95 h, following the 4S pathway. Its DBT desulfurization pattern was represented by the Michaelis-Menten equation. Various parameters such as V-mas, K-m, mu(m), K-s and maximum specific DBT desulfurization rate were calculated which are 0.092 mmol L-1 h(-1), 3.554 mmol L-1, 0.157 h(-1), 3.722 mmol L-1 and 0.192 mmol L-1 DBT g(-1) DCW (dry cell weight) h(-1), respectively. It can desulfurize 50%, of the sulfur content of Kuhemond heavy crude oil (KHC oil) with an initial sulfur content of 7.6%wt in 6 days. Its maximum specific desulfurization rate for KHC oil is equivalent to 0.005 g sulfur g(-1) DCW h(-1). The bacterium was isolated during a heavy crude oil biodesulfurization project initiated by PEDEC, a subsidiary of National. Iranian Oil Company. CONCLUSION: The KHC oil sulfur removal efficiency of the bacterium is approximately five times that of BBRC-9016 bacterium. It removes sulfur selectively without using sulfur-containing compounds as its carbon source. By applying various media during its isolation, the probability of screening the correct microorganism is increased. (C) 2008 Society of Chemical Industry