Sulfur Oxygenase Reductase in Different <i>Acidithiobacillus Caldus</i>-Like Strains

Abstract

The elemental sulfur oxidising enzyme Sulfur Oxygenase Reductase (SOR) is very well investigated in acidothermophilic archaea, such as Acidianus brierleyi and Sulfolobus metallicus. In contrast, not much is known about the biochemistry of elemental sulfur oxidation in acidophilic bacteria. Recently, however, the SOR-encoding gene has been found also in a bacterial strain closely related to the moderate thermophile Acidithiobacillus caldus. Confusingly, for the latter species, also the involvement of the SOX system as well as thiosulfate:quinone oxidoreductase (TQO) and tetrathionate hydrolase (TTH) in sulfur compound oxidation has been proposed based on genome analysis. In this study, we have detected the sor-gene in other Acidithiobacillus caldus-like strains, isolated from various bioleaching habitats, indicating that SOR plays an important role in sulfur oxidation in this species. Based on sequence comparison, the new bacterial sor-genes are closely related and distant from the known archaeal sequences as well as from the SOR found in the neutrophilic bacterium Aquifex aeolicus. In addition, SOR activity has been detected in crude cell extracts from all Acidithiobacillus caldus-like strains tested. The enzyme is truly thermophilic as highest activities were achieved at 65 °C, which is far beyond the growth optimum of Acidithiobacillus caldus. This finding may give rise to the question whether the presence of SOR in Acidithiobacillus caldus is only relevant while growing at elevated temperatures. Currently, experiments are performed for testing this hypothesis (comparing growth and enzyme activities at 30 vs. 45 °C).

Sulfur Oxygenase Reductase (Sor) in the Moderately Thermoacidophilic Leaching Bacteria: Studies in Sulfobacillus thermosulfidooxidans and Acidithiobacillus caldus

“…Previously, we had reported Sor activity in At. caldus S1 and S2 strains [ 40 ]. However, after several attempts we could not detect Sor activity in any of the seven At.…”

“…Previously we reported the presence of Sor enzyme activity in At. caldus strains S1 and S2 [ 40 ]. However, our attempts to measure Sor activity in At.…”

Sulfur Metabolism in the Extreme Acidophile Acidithiobacillus Caldus

“…This suggests the presence of potentially shared regulatory regions that could be co-regulating both enzymes, catalyzing successive reactions, and thus providing an adaptive strategy. Recently, the enzyme activity of Sor has been reported to be present in A. caldus -like strains (Janosch et al, 2009). However, it is still unknown how its substrate (S 8 ) is incorporated in to the cell or how the resulting products (S 0 , H 2 S, and ${\text{S}}_{\text{2}}{\text{O}}_{\beta }^{-2}$) are excreted.…”

Persulfide Dioxygenase From Acidithiobacillus caldus: Variable Roles of Cysteine Residues and Hydrogen Bond Networks of the Active Site

“…The SDO2 protein is 99% identical to the PDO described here. The deletion or overexpression of both sdo genes did not affect the growth properties of MTH-04 on elemental sulfur significantly ( Wu et al, 2017 ) suggesting that other sulfur-oxidizing enzymes like the sulfur oxygenase reductase ( Janosch et al, 2009 , 2015 ) might be more important. A deletion of the sdo1 gene, however, resulted in a complete inability of MTH-04 to grow on tetrathionate ( Wu et al, 2017 ).…”