Biodesulfurization of Naphthothiophene and Benzothiophene through Selective Cleavage of Carbon-Sulfur Bonds by Rhodococcus sp. Strain WU-K2R

Abstract

Naphtho[2,1-b]thiophene (NTH) is an asymmetric structural isomer of dibenzothiophene (DBT), and in addition to DBT derivatives, NTH derivatives can also be detected in diesel oil following hydrodesulfurization treatment. Rhodococcus sp. strain WU-K2R was newly isolated from soil for its ability to grow in a medium with NTH as the sole source of sulfur, and growing cells of WU-K2R degraded 0.27 mM NTH within 7 days. WU-K2R could also grow in the medium with NTH sulfone, benzothiophene (BTH), 3-methyl-BTH, or 5-methyl-BTH as the sole source of sulfur but could not utilize DBT, DBT sulfone, or 4,6-dimethyl-DBT. On the other hand, WU-K2R did not utilize NTH or BTH as the sole source of carbon. By gas chromatography-mass spectrometry analysis, desulfurized NTH metabolites were identified as NTH sulfone, 2-hydroxynaphthylethene, and naphtho Sulfur oxides generated by combustion of fossil fuel lead to acid rain and air pollution. Therefore, today petroleum is treated by hydrodesulfurization (HDS) using metallic catalysts in the presence of hydrogen gas under extremely high temperature and pressure. Although HDS can remove various types of sulfur compounds, some types of heterocyclic sulfur compounds cannot be removed. Dibenzothiophene (DBT) is one such recalcitrant organosulfur compound and is widely recognized as a model target compound for deeper desulfurization, since DBT derivatives can be detected in diesel oil following HDS treatment. Therefore, the application of a biodesulfurization process using a DBT-desulfurizing microorganism following HDS, mainly for diesel oil, has attracted attention for achievement of deeper desulfurization (16,20). Some mesophilic and thermophilic DBT-desulfurizing microorganisms have been isolated, for example, Rhodococcus sp. strain IGTS8 (1, 4, 21, 22), Rhodococcus erythropolis D-1 (8), R. erythropolis H-2 (17, 18), R. erythropolis KA2-5-1 (6), and Paenibacillus sp. strain A11-2, which desulfurizes DBT at 60°C (7, 11). We have also isolated Bacillus subtilis WU-S2B (9) and Mycobacterium phlei WU-F1 (2), which could desulfurize DBT and its derivatives over a wide temperature range of 20 to 50°C and at the highest level at 45 to 50°C. These bacteria desulfurize DBT through the sulfur-specific degradation pathway with the selective cleavage of carbon-sulfur (C-S) bonds without reducing the energy content (4,21,22). Naphtho[2,1-b]thiophene (NTH) (see Fig. 3B), which includes a benzothiophene (BTH) (see Fig. 3A) structure, is an asymmetric structural isomer of DBT. Recently it has become apparent that in addition to DBT derivatives, NTH derivatives can also be detected in diesel oil following HDS treatment, although NTH derivatives are minor components in comparison with DBT derivatives (unpublished data). Therefore, NTH may also be a model target compound for deeper desulfurization. Kropp et al. (13) have reported that Pseudomonas sp. strain W1 could degrade NTH. However, this bacterium utilized NTH as the carbon source with reducing the energy content, and the sulfur atom was not remo...

Aerobic Degradation of Petroleum Components by Microbial Consortia

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Use of a Novel Fluorinated Organosulfur Compound To Isolate Bacteria Capable of Carbon-Sulfur Bond Cleavage

“…Recently, a metabolic pathway has been described for Rhodococcus sp. strain WU-K2R that can desulfurize naphthothiophene and benzothiophene (21).…”

Effects of nicotinamide and riboflavin on the biodesulfurization activity of dibenzothiophene by Rhodococcus erythropolis USTB-03

“…Although chemical-physical processes can be used to remove inorganic sulfur from crude fuels, organic sulfur in dibenzothiophene (DBT), a widely used model of organic sulfur compound, remains in petroleum and coal even after these processes (Gray et al, 1996). To overcome this problem, some promising bacterial strains are identified to remove sulfur from DBT through the sulfur-specific pathway, which is capable of obtaining nutritional sulfur from DBT and producing 2-hydroxybiphenyl (2HBP) as the final product without causing oxidative loss of fuel carbon, which is the most efficient means for the desulfurization of DBT (Yan et al, 2000;Furuya et al, 2001;Kirimura et al, 2002;Li et al, 2005;Ishii et al, 2005;Yang and Marison, 2005;Gunam et al, 2006).…”