Dibenzothiophene (DBT) degradation activity of recombinant Rhodococcus sp. T09/pRKPP was increased by about 3.5-fold by introduction of the NAD(P)H/FMN oxidoreductase gene (dszD), while DBT desulfurization activity remained the same with production of dibenzo[1,2]oxathiin-6-oxide, which was caused by insufficient activity of the last desulfurization step involving a desulfinase. Introduction of an additional dsz operon resulted in a 3.3-fold increase DBT desulfurization activity (31 mu mol g dry cell(-1) h(-1)) compared with that of T09/pRKPP (9.5 mu mol g dry cell(-1) h(-1)). Furthermore, optimization of DBT at 25 mg l(-1) and glucose at 10 g l(-1), increased the total DBT desulfurization activity 2- to 3-fold due to increases in the DBT desulfurizing specific activity and the final cell concentration.