Novel Genes of the dsr Gene Cluster and Evidence for Close Interaction of Dsr Proteins during Sulfur Oxidation in the Phototrophic Sulfur Bacterium Allochromatium vinosum

Abstract

Seven new genes designated dsrLJOPNSR were identified immediately downstream of dsrABEFHCMK, completing the dsr gene cluster of the phototrophic sulfur bacterium Allochromatium vinosum D (DSM 180 T ). Interposon mutagenesis proved an essential role of the encoded proteins for the oxidation of intracellular sulfur, an obligate intermediate during the oxidation of sulfide and thiosulfate. While dsrR and dsrS encode cytoplasmic proteins of unknown function, the other genes encode a predicted NADPH:acceptor oxidoreductase (DsrL), a triheme c-type cytochrome (DsrJ), a periplasmic iron-sulfur protein (DsrO), and an integral membrane protein (DsrP). DsrN resembles cobyrinic acid a,c-diamide synthases and is probably involved in the biosynthesis of siro(heme)amide, the prosthetic group of the dsrAB-encoded sulfite reductase. The presence of most predicted Dsr proteins in A. vinosum was verified by Western blot analysis. With the exception of the constitutively present DsrC, the formation of Dsr gene products was greatly enhanced by sulfide. DsrEFH were purified from the soluble fraction and constitute a soluble ␣ 2 ␤ 2 ␥ 2 -structured 75-kDa holoprotein. DsrKJO were purified from membranes pointing at the presence of a transmembrane electron-transporting complex consisting of DsrKMJOP. In accordance with the suggestion that related complexes from dissimilatory sulfate reducers transfer electrons to sulfite reductase, the A. vinosum Dsr complex is copurified with sulfite reductase, DsrEFH, and DsrC. We therefore now have an ideal and unique possibility to study the interaction of sulfite reductase with other proteins and to clarify the long-standing problem of electron transport from and to sulfite reductase, not only in phototrophic bacteria but also in sulfate-reducing prokaryotes.Phototrophic purple and green sulfur-oxidizing bacteria use sulfur compounds as electron donors for reductive carbon dioxide fixation during photolithotrophic growth (7, 10). In these organisms, light energy is used to transfer electrons from sulfur compounds to the level of the more highly reducing electron carriers NAD(P) ϩ and ferredoxin. In our laboratory we seek to understand oxidative sulfur metabolism in anoxygenic phototrophic bacteria by using the genetically accessible ␥-proteobacterium Allochromatium vinosum (formerly Chromatium vinosum [34]) as our model organism. It is a purple sulfur bacterium belonging to the family Chromatiaceae. A. vinosum carries out the complete eight-electron oxidations of sulfide and thiosulfate to sulfate. Intracellularly stored sulfur globules are an obligate intermediate in the process (57). The sulfur in the globules is present in the molecular structure of sulfur chains (58) and is enclosed by a protein envelope, a feature shared by most if not all of the chemotrophic sulfur-oxidizing bacteria that form intracellular sulfur globules (9, 14, 51). Topologically, the sulfur globules of A. vinosum and probably of other members of the Chromatiaceae are located extracytoplasmically, in the periplasm (51).O...

Sulfur globule oxidation in green sulfur bacteria is dependent on the dissimilatory sulfite reductase system

“…The same observation has been made in studies of dsr mutants of A. vinosum (Dahl et al, 2005). All sequenced GSB contain the same dsr genes (dsrNCABLUEFHTMKJO-PVW), suggesting that the DSR system functions in the same manner in all GSB.…”

“…MC-1) contain a putative sulfur transferase complex (DsrEFH) and an ironsulfur flavoprotein with NADH oxidoreductase activity (DsrL). Individual gene inactivation of dsrA, dsrB, dsrH, dsrM, dsrK, dsrL, dsrJ, dsrO and dsrP completely prevents oxidation of sulfur globules in A. vinosum, whereas individual gene inactivation of dsrN and dsrR significantly reduces the oxidation rate of sulfur globules (Dahl et al, 2005;Grimm et al, 2010;Lübbe et al, 2006;Pott & Dahl, 1998;Sander et al, 2006).…”

“…1). The only genes known to be essential for oxidation of sulfur globules in PSB are the dsr genes, which in A. vinosum are located in a single cluster, dsrABEFHCMKLJOPNRS (Dahl et al, 2005). These genes encode a dissimilatory sulfite reductase (DSR) system that is homologous to that in sulfatereducing bacteria but operates in the reverse (oxidative) direction.…”

Genomic insights into the uncultured genus ‘Candidatus Magnetobacterium’ in the phylum Nitrospirae

“…One gene (Peg.0221) encodes a protein with considerable similarity to sulfide:quinone oxidoreductase (sqr), which could catalyze the oxidation of sulfide (S 2 À ) to elemental sulfur (S 0 ) (Pott and Dahl, 1998;Reinartz et al, 1998). Elemental sulfur could be further oxidized to sulfite by the dissimilatory sulfite reductase encoded by dsrABDEFH genes that have been found in the sequenced genome (Dahl et al, 2005;Holkenbrink et al, 2011). In addition, genes for adenosine 5 0 -phosphosulfate reductase (Peg.0013 and Peg.0014, aprAB) and adenosine 5 0 -triphosphate (ATP) sulfurylase (Peg.0012, sat) mediating the oxidation of sulfite to sulfate have also been found in the genome.…”

Sulfite oxidation in the purple sulfur bacterium Allochromatium vinosum: identification of SoeABC as a major player and relevance of SoxYZ in the process

“…This is evidenced by the presence of signal peptide-encoding sequences in the genes for the three structural proteins constituting the sulfur globule envelope (Pattaragulwanit et al, 1998;Prange et al, 2004;Frigaard & Dahl, 2008). For further oxidation of stored sulfur, the so-called Dsr system is of essential importance (Pott & Dahl, 1998;Dahl et al, 2005;Lübbe et al, 2006;Sander et al, 2006). The product of the Dsr pathway is sulfite, generated by a reverse-acting dissimilatory sulfite reductase (DsrAB), an enzyme that is well known to be located in the cytoplasm (Hipp et al, 1997;Pott & Dahl, 1998;Frigaard & Dahl, 2008).…”