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

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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 α2β2γn(n ≥ 2) multimer with a native size of 285 kDa as determined by gel filtration. We have sequenced the genes encoding the α and β subunits (dsrA and dsrB, respectively), which probably constitute one operon. dsrAand dsrB encode polypeptides of 49 (α) and 54 kDa (β) which show significant similarities to the homologous subunits of other DSRs. The dsrB gene product of B. wadsworthiais apparently a fusion protein of dsrB anddsrD. 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 thatB. wadsworthia grouped with its closest 16S rDNA relative Desulfovibrio desulfuricans Essex 6.

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