Bioenergetic Aspects of Dibenzothiophene Desulfurization by Growing Cells of Ralstonia eutropha

The present study focuses on effects of initial pH on dibenzothiophene (DBT) desulfurization via 4S pathway by growing cells of Ralstonia eutropha. For so doing, temporal changes of biomass concentration, glucose as a sole carbon source, pH value, and 2-hydroxybiphenyl (2-HBP) formation have been monitored during the bioprocess. The biomass concentration has been modeled by the logistic equation and results show that the values of maximum specific growth rate (μmax) and maximum cell concentration (Xmax) have increased in line with the rise of initial pH from 6 to 9. This confirms the effect of pH on the energetics of cell growth via altering the proton gradient and manipulating ATP-related metabolic pathways. By considering the Pirt’s maintenance concept, the bioenergetic aspects of DBT desulfurization process are affected by changes in pH, where the maximum specific DBT conversion rate (0.0014 mmol/gcell.h) has been obtained at initial pH of 8. Additionally, the kinetic modeling of the 2-HBP formation through the Luedeking-Piret model indicates that the DBT desulfurization rate is linearly related to the cell growth rate, instead of biomass concentration. The growth associated and non-growth associated 2-HBP formation constants have been obtained 3.82 mg2-HBP/gcell and 0.06 mg2-HBP/gcell.h, respectively at an initial pH of 8.