Thiosulphate oxidation in the phototrophic sulphur bacterium Allochromatium vinosum

Abstract

SummaryTwo different pathways for thiosulphate oxidation are present in the purple sulphur bacterium Allochromatium vinosum: oxidation to tetrathionate and complete oxidation to sulphate with obligatory formation of sulphur globules as intermediates. The tetrathionate:sulphate ratio is strongly pH-dependent with tetrathionate formation being preferred under acidic conditions. Thiosulphate dehydrogenase, a constitutively expressed monomeric 30 kDa c-type cytochrome with a pH optimum at pH 4.2 catalyses tetrathionate formation. A periplasmic thiosulphateoxidizing multienzyme complex (Sox) has been described to be responsible for formation of sulphate from thiosulphate in chemotrophic and phototrophic sulphur oxidizers that do not form sulphur deposits. In the sulphur-storing A. vinosum we identified five sox genes in two independent loci (soxBXA and soxYZ). For SoxA a thiosulphate-dependent induction of expression, above a low constitutive level, was observed. Three sox-encoded proteins were purified: the heterodimeric c-type cytochrome SoxXA, the monomeric SoxB and the heterodimeric SoxYZ. Gene inactivation and complementation experiments proved these proteins to be indispensable for thiosulphate oxidation to sulphate. The intermediary formation of sulphur globules in A. vinosum appears to be related to the lack of soxCD genes, the products of which are proposed to oxidize SoxY-bound sulphane sulphur. In their absence the latter is instead transferred to growing sulphur globules.

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

“…Once formed, thiosulfate could obviously no longer be transformed into sulfate in the DsoxY strain. This result is in complete agreement with earlier findings that tetrathionate is the only product of thiosulfate-exposed A. vinosum DsoxY cells (Hensen et al, 2006). The inability of the DsoxY strain to form sulfate from thiosulfate is clearly due to the incompleteness of the Sox system.…”

“…For the insertional inactivation of Characterization of phenotypes, detection of sulfur species and protein determination. A. vinosum WT and mutant strains were characterized in batch culture experiments essentially as described previously (Prange et al, 2004;Hensen et al, 2006). Cells of A. vinosum, grown photo organoheterotrophically on malate [RCV medium (Weaver et al, 1975)] for 3 days were used as an inoculum for experiments concerned with transformation of sulfide and sulfite.…”

“…Notably, Friedrich and coworkers proved this reaction to be independent of the presence of SoxCD, a molybdohaemoprotein catalysing the six-electron oxidation of SoxY-cysteine-bound persulfide to sulfone sulfur. Purple bacteria that form sulfur globules during thiosulfate oxidation contain the Sox system, albeit without the SoxCD proteins (Hensen et al, 2006;Frigaard & Dahl, 2008).…”

“…The first major process in the oxidation of thiosulfate and sulfide is the formation of intracellularly stored sulfur globules. The oxidation of thiosulfate to sulfate with sulfur globules as an intermediate involves the periplasmic Sox proteins SoxYZ, SoxB, SoxXAK and SoxL (Pott & Dahl, 1998;Hensen et al, 2006;Welte et al, 2009). For the oxidation of sulfide, A. vinosum possesses the genetic equipment for at least three different enzymes catalysing this reaction, namely the soluble periplasmic flavocytochrome c and the membrane-bound sulfide : quinone oxidoreductases SqrD and SqrF.…”

Utilization of solid ‘elemental’ sulfur by the phototrophic purple sulfur bacterium Allochromatium vinosum: a sulfur K-edge X-ray absorption spectroscopy study

“…Alc. vinosum DSMZ 180 T was cultivated photolithoautotrophically in batch culture at 30 uC under anaerobic conditions for 5 days in a thermostatted glass fermenter (culture volume 1.6 l) containing modified Pfennig's medium (0 medium without sulfide) (Hensen et al, 2006). Solid elemental sulfur (S 0 ; 50 mM) was added as the sole sulfur source to the culture.…”