Interactive effects in biodesulfurization of model oil containing dibenzothiophene and 4,6-dimethyl dibenzothiophene using Rhodococcus rhodochrous MTCC 3552

Abstract

This paper reports investigations into the biodesulfurization process in a dual substrate system. The model system comprises dibenzothiophene (DBT) and 4,6-dimethyl dibenzothiophene (4,6-DMDBT) as substrates and microbial strains of Rhodococcus rhodochrous. Experiments were conducted for single and dual substrate systems using different combinations of concentrations. The experimental results were analyzed using mathematical models for competitive kinetics with self-inhibition and competitive kinetics with uncompetitive self- and cross-inhibition. In the concentration range of 50–150 ppm, the enzyme affinity (Monod constant) of 4,6-DMDBT (4.25–4.83 mM) is higher than that of DBT (4.83–6.13 mM). As compared to single substrate system, the biodegradation velocity of DBT reduced to a lesser extent (35–69 %) than 4,6-DMDBT (45–76 %) in dual substrate system. No inhibition (either self or cross) was seen for the present biodesulfurization system. Retardation of biodegradation velocities was higher for relatively larger contents of 4,6-DMDBT, plausibly due to a decrease in membrane fluidity and permeability.