ABSTRACTAcidithiobacillus caldus
has been proposed to play a role in the oxidation of reduced inorganic sulfur compounds (RISCs) produced in industrial biomining of sulfidic minerals. Here, we describe the regulation of a new cluster containing the gene encoding tetrathionate hydrolase (
tetH
), a key enzyme in the RISC metabolism of this bacterium. The cluster contains five cotranscribed genes, IS
ac1
,
rsrR
,
rsrS
,
tetH
, and
doxD
, coding for a transposase, a two-component response regulator (RsrR and RsrS), tetrathionate hydrolase, and DoxD, respectively. As shown by quantitative PCR,
rsrR
,
tetH
, and
doxD
are upregulated to different degrees in the presence of tetrathionate. Western blot analysis also indicates upregulation of TetH in the presence of tetrathionate, thiosulfate, and pyrite. The
tetH
cluster is predicted to have two promoters, both of which are functional in
Escherichia coli
and one of which was mapped by primer extension. A pyrrolo-quinoline quinone binding domain in TetH was predicted by bioinformatic analysis, and the presence of an
o
-quinone moiety was experimentally verified, suggesting a mechanism for tetrathionate oxidation.