A new isolated dibenzothiophene (DBT) desulfurizing bacterium, identified as Mycobacterium sp. ZD-19 can utilize a wide range of organic sulfur compounds as a sole sulfur source. Thiophene (TH) or benzothiophene (BTH) was completely degraded by strain ZD-19 within 10 h or 42 h, and 100% DBT or 4,6-dimethyldibenzothiophene (4,6-DMDBT) was removed within 50 It or 56 h, respectively. Diphenylsulfide (DPS) possessed the lowest desulfurization efficiencies with 60% being transformed within 50 h and 80% at 90 It. The desulfurization activities of five substrates by resting cells are in order of TH > BTH > DPS > DBT > 4,6-DMDBT. In addition, when DBT and 4,6-DMDBT were mixed, they could be simultaneously desulfurized by strain ZD-19. However, DBT appeared to be attacked prior to 4.6-DMDBT. The desulfurization rate of DBT or 4,6-DMDBT in mixture is lower than they are desulfurized separately, indicating that the substrate competitive inhibition is existent when DBT and 4,6-DMDBT are mixed. (C) 2007 Elsevier Ltd. All rights reserved.