Gene Identification and Substrate Regulation Provide Insights into Sulfur Accumulation during Bioleaching with the Psychrotolerant Acidophile Acidithiobacillus ferrivorans

Abstract

The psychrotolerant acidophile Acidithiobacillus ferrivorans has been identified from cold environments and has been shown to use ferrous iron and inorganic sulfur compounds as its energy sources. A bioinformatic evaluation presented in this study suggested that Acidithiobacillus ferrivorans utilized a ferrous iron oxidation pathway similar to that of the related species Acidithiobacillus ferrooxidans. However, the inorganic sulfur oxidation pathway was less clear, since the Acidithiobacillus ferrivorans genome contained genes from both Acidithiobacillus ferrooxidans and Acidithiobacillus caldus encoding enzymes whose assigned functions are redundant. Transcriptional analysis revealed that the petA1 and petB1 genes (implicated in ferrous iron oxidation) were downregulated upon growth on the inorganic sulfur compound tetrathionate but were on average 10.5-fold upregulated in the presence of ferrous iron. In contrast, expression of cyoB1 (involved in inorganic sulfur compound oxidation) was decreased 6.6-fold upon growth on ferrous iron alone. Competition assays between ferrous iron and tetrathionate with Acidithiobacillus ferrivorans SS3 precultured on chalcopyrite mineral showed a preference for ferrous iron oxidation over tetrathionate oxidation. Also, pure and mixed cultures of psychrotolerant acidophiles were utilized for the bioleaching of metal sulfide minerals in stirred tank reactors at 5 and 25°C in order to investigate the fate of ferrous iron and inorganic sulfur compounds. Solid sulfur accumulated in bioleaching cultures growing on a chalcopyrite concentrate. Sulfur accumulation halted mineral solubilization, but sulfur was oxidized after metal release had ceased. The data indicated that ferrous iron was preferentially oxidized during growth on chalcopyrite, a finding with important implications for biomining in cold environments.

Microbial biogeochemistry of Boiling Springs Lake: a physically dynamic, oligotrophic, low‐pH geothermal ecosystem

“…6). is likely, especially in oxic-anoxic transition zones and the majority of the lake water where temperature and sulfate concentrations predict significantly decreased oxygen concentrations compared to atmospheric levels (Liljeqvist et al, 2013). Chemosynthetic primary production is likely driven by the (micro)aerobic oxidation of reduced iron and sulfur minerals by members of the Firmicutes and Actinobacteria phyla, the cproteobacterium Acidithiobacillus spp., and Archaea in the Sulfolobaceae family.…”

“…Additionally, hydrogen-mediated primary production via Hydrogenobaculum spp. is likely, especially in oxic-anoxic transition zones and the majority of the lake water where temperature and sulfate concentrations predict significantly decreased oxygen concentrations compared to atmospheric levels (Liljeqvist et al, 2013). Carboxydotrophy also seems to play a role in organic synthesis in this ecosystem, although the identity of the carboxydotrophs is 6 Model of Boiling Springs Lake biogeochemistry.…”

Acidithiobacillus ferrivorans SS3 presents little RNA transcript response related to cold stress during growth at 8 °C suggesting it is a eurypsychrophile

“…Two At. ferrivorans strains have been genome sequenced (Liljeqvist et al 2011; Talla et al 2013) and potential genes involved in iron and ISC oxidation have been identified (Liljeqvist et al 2013). Transcriptomes analyses were used to identify the expression of At.…”

Microbial copper resistance: importance in biohydrometallurgy

“…The A. ferrivorans SS3 genome contains two additional copies of the rus gene (Liljeqvist et al ., ) and its three Rus proteins not only have a high Blastp score (>85%) to Rus from A. ferrooxidans but all of them also conserve the same copper‐binding site. RusA from A. ferrivorans SS3 is the protein with the highest identity compared with Rus from A. ferroxidans and it forms part of the rus operon from A. ferrivorans together with the gene coding for the AcoP protein (Liljeqvist et al ., ).…”

“…The A. ferrivorans SS3 genome contains two additional copies of the rus gene (Liljeqvist et al ., ) and its three Rus proteins not only have a high Blastp score (>85%) to Rus from A. ferrooxidans but all of them also conserve the same copper‐binding site. RusA from A. ferrivorans SS3 is the protein with the highest identity compared with Rus from A. ferroxidans and it forms part of the rus operon from A. ferrivorans together with the gene coding for the AcoP protein (Liljeqvist et al ., ). In the light of the recent report suggesting that Rus and AcoP are copper resistance determinants in A. ferrooxidans ATCC 23270 (Navarro et al ., ), it will be of interest to study whether these proteins have a similar role in copper resistance in A. ferrivorans .…”