Biodesulfurization of Dibenzothiophene (DBT) Using Pseudomonas putida CECT 5279: A Biocatalyst Formulation Comparison

Abstract

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Problems caused by sulfur oxide emissions to the atmosphere and restrictive legal limitations to sulfur content in fuels have made biodesulfurization (BDS) to be proposed as a complementary technology to hydrodesulfurization (HDS). In this work, a genetically modified microorganism, Pseudomonas putida CECT 5279, is employed as a desulfurizing biocatalyst. This microorganism has the ability of carrying out the metabolic 4S pathway from Rhodococcus erythropolis IGTS8, to desulfurize dibenzothiophene (DBT), as a model compound. In previous works (Martin, A. B.; Alcon, A.; Santos, V. E.; Garcia-Ochoa, F. Energy Fuels 2004, 18, 851-857 andMartin, A. B.; Alcon, A.; Santos, V. E.; Garcia-Ochoa, F.Energy Fuels 2005, 19, 775-782), a maximum of BDS capability to be employed as a resting cell BDS biocatalyst was observed in cells grown for nearly 9 h. In a recent work[Calzada, J.; Zamarro, M. T.; Alcon, A.; Santos, V. E.; Diaz, E.; Garcia, J. L.; Garcia-Ochoa, F. Appl. Environ. Microbiol. 2009, 75 (3), 875-877], the profile of intracellular enzymatic activity of every enzyme involved in the 4S route was elucidated to explain the maximum on BDS capability by cells observed during growth. Monooxygenase enzymes (DszA and DszC) show a maximum of in vivo activity when the late exponential growth phase is reached. However, desulfinase enzyme DszB shows a maximum of its activity in the early exponential growth phase. Results obtained with 9 h of growth time cells (simple biocatalyst) are compared to those obtained with cell mixtures where 5 and 23 h cells are combined (complex biocatalyst) because of their respective higher desulfinase and monooxygenase activities. Hereby, 50% biomass mixture of 5 and 23 h cells were found to have better BDS skills than 9 h cells. Different total biomass concentrations were tested by carrying out resting cell assays. In these experiments, DBT was used as the sulfur model compound. Maximum BDS percentage, XBDS max , time for maximum desulfurization, tBDSmax, and specific conversion rate, E, were the chosen parameters to compare the behavior of cells collected at 9 h and a cell mixture formed by cells collected at 5 and 23 h of growth.