Organic sulfur compounds found in petroleum lead to the formation of sulfur dioxide during combustion. Sulfur dioxide emissions can poison catalytic converters, cause acid deposition and increase diesel particulate emissions. Polycyclic aromatic sulfur heterocycles (PASHs), such as benzothiophene, account for a large fraction of this organic sulfur content (Liang et al., 2006). Microbial desulfurization processes are of particular interest as a means to reduce the petroleum sulfur content and minimize pollution.
Several microorganisms are able to incorporate the sulfur from benzothiophene into cell biomass. This desulfurization process involves sulfur-specific degradation via the cleavage of carbon-sulfur bonds. Benzothiophene is first oxidized to Benzothiophene-S,S-dioxide and subsequent thiophene ring opening via cleavage of the aryl C-S bond in a mechanism similar to dibenzothiophene desulfurization (Gilbert et al., 1998 and Kirimura et al., 2002). The final desulfination step in Gordona sp. strain 213E is thought to occur by oxygenase-catalyzed hydroxylation of the C-S carbon. In this case, an enol product is formed but quickly tautomerizes to the aldehyde upon release from the enzyme (Gilbert et al., 1998). If this aldehyde is oxidized to the carboxylate, it forms 2-hydroxyphenylacetate, a compound found in the styrene pathway. The desulfination product in Paenibacillus sp. strain A11-2 is o-hydroxystyrene via a sulfinase also capable of dibenzothiophene desulfination (Konishi et al., 2003).
Dibenzothiophene has both a desulfurization pathway and a pathway for complete metabolism of the compound. The latter pathway may also occur for benzothiophene.
The following is a text-format benzothiophene desulfurization pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This is the first pathway to have its map also available in graphic (8k) format.
Benzothiophene
Mycobacterium phlei WU-0103
Rhodococcus sp. strain WU-K2R
Gordona sp. strain 213E
Paenibacillus sp. strain A11-2
Sinorhizobium sp. KT55
|
|
| benzothiophene
| monooxygenase
|
v
Benzothiophene-S-oxide
|
|
| benzothiophene
| monooxygenase
|
v
Benzothiophene-S,S-dioxide
|
|
| benzothiophene-S,S-dioxide
| monooxygenase
|
v
(Z)-2-(2-Hydroxyphenyl)-
ethenesulfinate
|
+------------+------------+
| |
2'-hydroxybiphenyl- | v (Z)-2-(2-Hydroxyphenyl)-
2-sulfinate desulfinase | | ethenesulfinate oxidase
| |
v v
o-Hydroxystyrene 2-Hydroxyphenylacetaldehyde
Page Author(s): Michael Turnbull
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