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

Abstract

The DbtS ؉ phenotype (which confers the ability to oxidize selectively the sulfur atom of dibenzothiophene [DBT] or dibenzothiophene sulfone [DBTO 2 ]) 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 ؊1) was maximal at pH 5.5. Quantitative measurements in fermentors (in both batch and fed-batch modes) demonstrated that DBTO 2 as the sole sulfur source yielded a greater amount of product than did DBT. Specifically, 100 M DBT maximally yielded Ϸ40 M OH-BP, while 100 M DBTO 2 yielded Ϸ60 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 4 2؊ in growth media repressed expression of desulfurization activity, but SO 4 2؊ added to suspensions of cells grown in DBT or DBTO 2 did not inhibit desulfurization activity.

Flux-based analysis of sulfur metabolism in desulfurizing strains of Rhodococcus erythropolis

“…Several literature studies have reported the effect of sulfate on desulfurization activity. Li et al (1996) reported that although sulfate represses the dsz genes, it does not inhibit the activity of desulfurizing enzymes (Wang & Krawiec, 1996). They observed that the desulfurizing activity increased with decreasing amount of sulfate in the medium.…”

Continuous Desulfurization of Dibenzothiophene with Rhodococcus rhodochrous IGTS8 (ATCC 53968)

“…A biodesulfurization (BDS) process with biocatalyst production followed by biotransformation has been investigated previously. Rhodococcus rhodochrous has been grown in batch, fed batch (5,12,15), and continuous culture (16). DBT degradation was exclusively studied in batch or fed-batch mode (5,12,15).…”

“…Rhodococcus rhodochrous has been grown in batch, fed batch (5,12,15), and continuous culture (16). DBT degradation was exclusively studied in batch or fed-batch mode (5,12,15). As a commercial BDS process is likely to be operated continuously, we chose to study the feasibility of conducting the biotransformation reaction in a CSTR.…”

Kinetic Analyses of Desulfurization of Dibenzothiophene by Rhodococcus erythropolis in Continuous Cultures

“…The desulfurization phenotype of Rhodococcus erythropolis N1-36 (and other bacterial strains [3,8]) has the prospect of being the basis of a metabolically specific, ecologically benign, and economically attractive means of beneficiating fossil fuels (4,11). For a full assessment of the potential of N1-36, such features as maximum specific growth rate ( max ), saturation constant (K s ) (i.e., substrate concentration that yields a growth rate equal to one-half the theoretical maximum), cell yield coefficient (Y x/s ), and temperature dependence (or activation energy) of growth and desulfurization need to be determined.…”

“…Samples were taken after a steady state was established. During steady-state growth, concentrations of the substrate (DBTO 2 ) and product monohydroxybiphenyl (OH-BP) were determined by high-performance liquid chromatography (9, 10); biomass was estimated by converting culture optical densities to cell dry weights (by using standard curves [9][10][11]).…”