Summary auto-generated
Gordona sp. strain 213E, a novel bacterium isolated from soil, was shown to desulfurize benzothiophene (BTH) using BTH as its sole sulfur source while growing on mineral medium with fructose as carbon source. During growth, a phenolic compound accumulated that tested positive with Gibb's reagent. Analysis of metabolites extracted from culture medium identified the accumulated compound as 2-(2'-hydroxyphenyl)ethan-1-al (HPEal), the final product of BTH desulfurization. Gas chromatography-mass spectrometry identified six BTH metabolites, enabling construction of a proposed desulfurization pathway: BTH → benzothiophene S-oxide (BTHO) → benzothiophene S,S-dioxide (BTHO₂) → (Z)-2-(2'-hydroxyphenyl)ethen-1-sulphinate (HPESi⁻) → HPEal. This pathway parallels the known dibenzothiophene (DBT) desulfurization pathway of Rhodococcus sp. strain IGTS8, which produces 2-hydroxybiphenyl. However, Gordona strain 213E could not desulfurize DBT, and strain IGTS8 could not desulfurize BTH, demonstrating substrate specificity of the respective enzyme systems. Both pathways appear to function as sulfur-scavenging mechanisms repressed by readily available sulfate.
Key findings
- Gordona sp. strain 213E is the first reported bacterium capable of desulfurizing benzothiophene as a sole sulfur source for growth
- The BTH desulfurization pathway proceeds through sequential oxidation and ring-opening steps, producing 2-(2'-hydroxyphenyl)ethan-1-al as the final accumulated product
- BTH and DBT desulfurization pathways are substrate-specific with no cross-reactivity; strain 213E cannot metabolize DBT and strain IGTS8 cannot metabolize BTH
- Both BTH and DBT desulfurization appear to be sulfur-scavenging pathways repressed by more bioavailable inorganic sulfur sources
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Abstract
Gordona sp. strain 213E (NCIMB 40816) grew in pure culture in a mineral salts medium containing fructose as a source of carbon and energy, and benzothiophene (BTH) as the sole source of sulphur. During growth a phenolic compound accumulated, as indicated by the production of a blue colour on addition of Gibb's reagent. Therefore this pathway is analogous to the dibenzothiophene (DBT) desulphurization pathway of Rhodococcus sp. strain IGTS8, in which 2-hydroxybiphenyl accumulates during growth with DBT as the sole sulphur source. Ethyl acetate extraction of the culture medium yielded the metabolites benzothiophene s-oxide (BTHO), benzothiophene s,s-dioxide (BTHO2), benzo[c][1,2]oxathiin 6-oxide (BcOTO), 2-(2'-hydroxyphenyl) ethan 1-al (HPEal) and benzofuran (BFU). The deduced pathway for BTH desulphurization is BTH-->BTHO-->BTHO2-->HPESi(-)-->HPEal. HPESi- is (Z)-2-(2'-hydroxyphenyl)ethen 1-sulphinate, the stable aqueous-solution form of BcOTO. It was concluded that HPEal was the Gibb's-reagent- reactive phenolic compound which accumulated in the culture medium of strain 213E during growth, and that the presence of BFU was due to partial condensation of HPEal during the ethyl acetate extraction procedure. Gordona sp. strain 213E was unable to grow in a mineral salts medium containing fructose as a source of carbon and energy and DBT as the sole sulphur source. BTH-desulphurization-active cells (grown using BTH as sole sulphur source) were unable to desulphurize DBT. Likewise Rhodococcus sp. strain IGTS8 was unable to grow using BTH as the sole sulphur source, and DBT-desulphurization-active cells of strain IGTS8 (grown using DBT as sole sulphur source) were unable to desulphurize BTH. This absence of cross-reactivity is discussed in terms of fundamental differences in the chemistry of the DBT- and BTH- desulphurization reactions.