Dissimilatory Sulfite Reductase (Desulfoviridin) of the Taurine-Degrading, Non-Sulfate-Reducing Bacterium Bilophila wadsworthia RZATAU Contains a Fused DsrB-DsrD Subunit

Abstract

A dissimilatory sulfite reductase (DSR) was purified from the anaerobic, taurine-degrading bacterium Bilophila wadsworthia RZATAU to apparent homogeneity. The enzyme is involved in energy conservation by reducing sulfite, which is formed during the degradation of taurine as an electron acceptor, to sulfide. According to its UV-visible absorption spectrum with maxima at 392, 410, 583, and 630 nm, the enzyme belongs to the desulfoviridin type of DSRs. The sulfite reductase was isolated as an ␣ 2 ␤ 2 ␥ n (n > 2) multimer with a native size of 285 kDa as determined by gel filtration. We have sequenced the genes encoding the ␣ and ␤ subunits (dsrA and dsrB, respectively), which probably constitute one operon. dsrA and dsrB encode polypeptides of 49 (␣) and 54 kDa (␤) which show significant similarities to the homologous subunits of other DSRs. The dsrB gene product of B. wadsworthia is apparently a fusion protein of dsrB and dsrD. This indicates a possible functional role of DsrD in DSR function because of its presence as a fusion protein as an integral part of the DSR holoenzyme in B. wadsworthia. A phylogenetic analysis using the available Dsr sequences revealed that B. wadsworthia grouped with its closest 16S rDNA relative Desulfovibrio desulfuricans Essex 6.Bilophila wadsworthia is a strictly anaerobic, gram-negative bacterium (2) which belongs to the family Desulfovibrionaceae in the delta subdivision of the Proteobacteria, but does not reduce sulfate (2, 25). B. wadsworthia has been found quite frequently in patients with appendicitis and its complications and is the third most common anaerobic isolate in such infections (11), but can also be isolated from a wide variety of other infections, e.g., biliary tract infection (41), liver abscess (41), and ear infections (39). B. wadsworthia has also been found in the normal fecal flora (2). The organism lacks classical virulence factors like capsules, fimbriae, and extracellular enzymes (2). However, preliminary studies have indicated that B. wadsworthia exerts cytotoxic effects on two cell lines, and endotoxic activity of B. wadsworthia has been described (2, 34).We recently isolated from a communal sewage plant a strain of B. wadsworthia which utilizes organic sulfonates (e.g., taurine [2-aminoethanesulfonate]) as a carbon source and electron sink. B. wadsworthia respires taurine anaerobically with electrons derived mainly from formate oxidation and oxidation of the taurine carbon (25). Taurine is transaminated to sulfoacetaldehyde (22), which is cleaved to sulfite and an unidentified organic product (K. Denger and A. M. Cook, unpublished). Finally, sulfite is reduced to sulfide by a dissimilatory sulfite reductase (DSR) (6, 25). In addition, sulfite or thiosulfate serves as an electron acceptor for anaerobic respiration with formate as the electron donor in B. wadsworthia (25).DSR, a key enzyme in dissimilatory sulfate reduction, occurs in all organisms capable of reducing sulfite during anaerobic respiration investigated so far (9, 33). Otherwise, DSRs are rare....

Abundance and diversity of mucosa-associated hydrogenotrophic microbes in the healthy human colon

“…B. wadsworthia is a member of the mutualistic microbiota but has also been linked to gangrenous and perforated appendicitis in humans (Urban et al, 2004). This genus does not reduce sulfate but can use sulfite as a terminal electron acceptor during taurine metabolism in anaerobic respiration (Laue et al, 2001). It is important to acknowledge that the presence of SRB does not necessarily reflect the occurrence of sulfate reduction.…”

Abundance and diversity of sulphate-reducing bacterioplankton in Lake Suigetsu, a meromictic lake in Fukui, Japan

“…Desulfobacter vibrioformis, Desulfobulbus rhabdoformis (Larsen et al 2000), Desulfovibrio vulgaris (Karkhoff-Schweizer et al 1995), Desulfobacula toluolica (Zverlov et al 2005) and Archaeoglobus fulgidus (Dahl et al 1993) have only a single copy of the DSR gene but SRB existing in nature may have multiple copies of the DSR gene. Furthermore, some bacterial species incapable of sulphate reduction such as Desulfitobacterium halogenans (Klein et al 2001), Desulfitobacterium hafniense (Nonaka et al 2006), Bilophila wadsworthia (Lane et al 2001) and Sporotomaculum hydroxybenzoicum (Zverlov et al 2005) have the DSR gene. Therefore, our competitive PCR analysis probably overestimates the SBR population in situ.…”

Metabolic potential of fatty acid oxidation and anaerobic respiration by abundant members of Thaumarchaeota and Thermoplasmata in deep anoxic peat

“…However, detection of genes encoding for a desulfoviridin (dissimilatory sulfite reductase, dsrAB) implies Bg1 uses sulfite as a TEA, generating sulfide in a 6-electron transfer. The presence of an alkanesulfonate transporter, but no identifiable alkanesulfonate monooxygenase, suggests Bg1 may have an unknown mechanism for degrading organosulfonate to sulfite, possibly in a similar manner to sulfonate, but non-sulfate, reducing Bilophila wadsworthia, (Laue et al, 2001). The predicted Bg1 dsrA protein sequence was most closely related to those of thermophilic Crenarchaeota such as Thermoproteus and Volcanisaeta, by o60% sequence identity (Supplementary Figure S7), and thus represents a phylogenetically novel wetland dsrA gene (Pester et al, 2012).…”