Thiophenic compounds viz. dibenzothiophene (DBT) and its derivatives present in fossil fuels contribute significantly to air pollution. Here we report for the first time the efficacy of a strain of Achromobacter sp., isolated from a contaminated petroleum-oil soil sample, at efficiently cleaving carbon-sulfur (C-S) bonds in DBT under mesophilic growth conditions. This bacterium utilized DBT and its derivative viz. 4-methyl DBT as the sole source of sulfur and degraded them to 2-hydroxybiphenyl (2-HBP). The 2-HBP was finally converted to 2-methoxybiphenyl (2-MBP) by methylation at the hydroxyl group of 2-HBP suggesting that this bacterium followed sulfur-specific pathway (4S pathway) for deep-desulfurization. Further, 2-MBP is much less pollutant than DBT and therefore, it reduces the environmental pollution from fossil fuel combustion. Gas chromatography and X-ray fluorescence analyses revealed that the resting cells of Achromobacter sp. reduced 7.1% of the total sulfur content of diesel oil, obtained typically by treating 5 mL of diesel oil with 14 g of dry cell, without compromising the quality of diesel oil. For the industrial application, DBT desulfurization was optimized by using response surface methodology. Our study demonstrates that Achromobacter sp. is a potential candidate for biodesulfurization of diesel oil with anticipated application as an eco-friendly biodesulfurizing agent. (C) 2013 Elsevier B.V. All rights reserved.