Kinetic Analyses of Desulfurization of Dibenzothiophene by Rhodococcus erythropolis in Batch and Fed-Batch Cultures

The DbtS(sup+) phenotype (which confers the ability to oxidize selectively the sulfur atom of dibenzothiophene [DBT] or dibenzothiophene sulfone [DBTO(inf2)]) of Rhodococcus erythropolis N1-36 was quantitatively characterized in batch and fed-batch cultures. In flask cultures, production of the desulfurization product, monohydroxybiphenyl (OH-BP), was maximal at pH 6.0, while specific productivity (OH-BP cell(sup-1)) was maximal at pH 5.5. Quantitative measurements in fermentors (in both batch and fed-batch modes) demonstrated that DBTO(inf2) as the sole sulfur source yielded a greater amount of product than did DBT. Specifically, 100 (mu)M DBT maximally yielded (apprx=)40 (mu)M OH-BP, while 100 (mu)M DBTO(inf2) yielded (apprx=)60 (mu)M OH-BP. Neither maintaining the pH at 6.0 nor adding an additional carbon source increased the yield of OH-BP. The presence of SO(inf4)(sup2-) in growth media repressed expression of desulfurization activity, but SO(inf4)(sup2-) added to suspensions of cells grown in DBT or DBTO(inf2) did not inhibit desulfurization activity.