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Thiosulphate oxidation in the phototrophic sulphur bacterium Allochromatium vinosum
Author(s) -
Hensen Daniela,
Sperling Detlef,
Trüper Hans G.,
Brune Daniel C.,
Dahl Christiane
Publication year - 2006
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2006.05408.x
Subject(s) - tetrathionate , sulfur , biochemistry , periplasmic space , cytochrome , biology , bacteria , sulfur metabolism , cytochrome c , chemistry , gene , thiosulfate , enzyme , escherichia coli , organic chemistry , genetics , mitochondrion
Summary Two 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 thiosulphate‐oxidizing 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.