Biodesulfurization of fossil fuels by sulfolobus solfataricus P2

Abstract

Sulfur oxides emission upon fossil fuels combustion have been considered as a major cause of environmental pollution and acid rain. The conventional hydrodesulfurization (HDS) carried out with chemical catalysis at extremely high temperature (290-450oC) and pressure (1-20 mPa) is the current method for sulfur removal in fossil fuels, but it is not effective to remove heterocyclic organosulfur compounds such as dibenzothiophene (DBT) and substituted DBTs from the fuels. To overcome this problem biological desulfurization (BDS) has been proposed as an attractive alternative or complementary method regarding such heterocyclic organosulfur compounds for its low cost, mild reaction conditions and greater reaction specificity.The organism used in this study for BDS experiments is Sulfolobus solfataricus P2. The ability of the hyperthermophilic archaeon, Sulfolobus solfataricus P2, to grow on organic and inorganic sulfur sources such as dibenzothiophene (DBT), DBT-sulfone, BT, 4,6-dimethyldibenzothiophene, sodium sulfite, potassium disulfite, sodium sulfate, potassium persulfate and elemental sulfur were investigated. A sulfur free mineral medium has been employed and supplemented with different sources of carbon; glucose, arabinose, mannitol and ethanol, as well as different glucose concentrations (2, 5, 10, 15 and 20 g.L-1), to investigate the optimal sulfur free condition for the growth. Specific growth rate was increased and the length of the lag phase was markedly shortened when 20 g.L-1 glucose was employed as a sole source of carbon. Results showed that inorganic sulfur sources display a growth curve pattern significantly different from the curves obtained with organic sulfur sources. S. solfataricus P2 has an ability to utilize DBT and its derivatives, but it lacks BT utilization. When, biodesulfurization of 0.1 mM DBT was investigated in a minimal medium at 78oC, it was found that 88.5% of DBT was consumed by the microorganism and maximum desulfurization rate was obtained as 1.23 µmol 2-HBP h-1 g DCW-1 growing cells within 16.5 h. Isolation and characterization of a flavin reductase homolog gene from S. solfataricus enabled us to further study its contribution to biodesulfurization using recombinant technologies.Therefore, S. solfataricus P2 offers beneficial properties than other desulfurizing mesophilic and/or moderate thermophilic bacteria in the biodesulfurization process of fossil fuels due to its capacity to effectively utilize DBT and its derivatives at hyperthermophilic conditions by the cleavage of carbon-sulfur bond, without lowering the calorific value of fossil fuels.