Abstract
The sulfur oxygenase reductase (Sor) catalyzes the oxygen dependent disproportionation of elemental sulfur, producing sulfite, thiosulfate and sulfide. Being considered an “archaeal like” enzyme, it is also encoded in the genomes of some acidophilic leaching bacteria such as Acidithiobacillus caldus, Acidithiobacillus thiooxidans, Acidithiobacillus ferrivorans and Sulfobacillus thermosulfidooxidans, among others. We measured Sor activity in crude extracts from Sb. thermosulfidooxidans DSM 9293T. The optimum temperature for its oxygenase activity was achieved at 75 °C, confirming the “thermophilic” nature of this enzyme. Additionally, a search for genes probably involved in sulfur metabolism in the genome sequence of Sb. thermosulfidooxidans DSM 9293T was done. Interestingly, no sox genes were found. Two sor genes, a complete heterodisulfidereductase (hdr) gene cluster, three tetrathionate hydrolase (tth) genes, three sulfide quinonereductase (sqr), as well as the doxD component of a thiosulfate quinonereductase (tqo) were found. Seven At. caldus strains were tested for Sor activity, which was not detected in any of them. We provide evidence that an earlier reported Sor activity from At. caldus S1 and S2 strains most likely was due to the presence of a Sulfobacillus contaminant.
Highlights
Control of biological sulfur oxidation is important in bioleaching operations for the industrial bioleaching of metal sulfides or heavy metal recovery from industrial wastes [1]
In this article we report that Sb. thermosulfidooxidans DSM 9293T crude extracts possess sulfur oxygenase reductase (Sor) activity
After observing the presence of sor genes encoded in genomes of sulfobacilli, we measured Sor activity in crude extracts of Sb. thermosulfidooxidans
Summary
Control of biological sulfur oxidation is important in bioleaching operations for the industrial bioleaching of metal sulfides or heavy metal recovery from industrial wastes [1]. Thermoacidophilic leaching bacteria such as At. caldus and Sb. thermosulfidooxidans, are frequently found in leaching operations [2,3]. Sulfobacillus are Gram-positive, rod shaped, spore forming bacteria able to use S°, reduced inorganic sulfur compounds (RISC), ferrous iron and/or metal sulfide minerals as energy sources under chemolithoautotrophic or mixotrophic conditions [4]. At. caldus is a moderately thermophilic acidophilic Gram-negative bacterium able to chemolithoautotrophically oxidize S°and RISC such as tetrathionate or thiosulfate [9]. It cannot oxidize ferrous iron or pyrite, it can grow on RISCs resulting from pyrite oxidation in combination with iron oxidizers like Leptospirillum spp. It cannot oxidize ferrous iron or pyrite, it can grow on RISCs resulting from pyrite oxidation in combination with iron oxidizers like Leptospirillum spp. [10]
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