DBT desulfurization by Rhodococcus erythropolis PTCC 1767 in aqueous and biphasic systems

The biodesulfurization of dibenzothiophene (DBT) by growing and resting cells of Rhodococcus erythropolis PTCC 1767 was studied in this work. The effects of Tween 80 on cell growth and its DBT desulfurization ability were investigated in both aqueous and two-phase systems. The growth-supportive behavior of Tween 80 along with its role in increasing the DBT solubility provided an effective biocatalytic activity in the resting cells assay. The desulfurization capability was also dependent on the hydrocarbon fraction phase and the initial concentration of DBT. Three oil phase fractions of 25, 50, and 75%v/v were tested to evaluate the influence of oil phase presence on DBT desulfurization efficiency. A further decrease in desulfurization ability was occurred at higher oil phase ratios mainly due to a higher mass transfer limitation and lower DBT bioavailability. In the biphasic system, the increment of DBT desulfurization yield was followed by increasing DBT concentration up to 3.5 mM, and thereafter, the cessation of increasing trend occurred. Maximum specific production rate of 2-hydroxybiphenyl (2-HBP) with oil phase fraction of 25%v/v was obtained 0.0055 mmol g(-1) h(-1) at initial DBT and Tween 80 concentrations of 3.5 and 6 mM, respectively. Finally, kinetics of DBT desulfurization by growing cells in aqueous and biphasic systems were best fitted by the Haldane and Michaelis-Menten equations, respectively. The desulfurization activity of R. erythropolis was not repressed in the biphasic system for DBT concentration up to 7.13 mM, while product inhibition was observed at DBT concentration higher than 0.45 mM in the aqueous system.