A high-molecular-weight c-type cytochrome, Cyc2, and a putative 22-kDa c-type cytochrome were detected in the membrane fraction released during spheroplast formation from Acidithiobacillus ferrooxidans. This fraction was enriched in outer membrane components and devoid of cytoplasmic membrane markers. The genetics, as well as the subcellular localization of Cyc2 at the outer membrane level, therefore make it a prime candidate for the initial electron acceptor in the respiratory pathway between ferrous iron and oxygen.
The regulation of the expression of the rus operon, proposed to encode an electron transfer chain from the outer to the inner membrane in the obligate acidophilic chemolithoautroph Acidithiobacillus ferrooxidans, has been studied at the RNA and protein levels. As observed by Northern hybridization, real-time PCR and reverse transcription analyses, this operon was more highly expressed in ferrous iron- than in sulfur-grown cells. Furthermore, it was shown by immunodetection that components of this respiratory chain are synthesized in ferrous iron- rather than in sulfur-growth conditions. Nonetheless, weak transcription and translation products of the rus operon were detected in sulfur-grown cells at the early exponential phase. The results strongly support the notion that rus-operon expression is induced by ferrous iron, in agreement with the involvement of the rus-operon-encoded products in the oxidation of ferrous iron, and that ferrous iron is used in preference to sulfur.
The chemolithoautotrophic Gram-negative bacterium Acidithiobacillus ferrooxidans is versatile and can grow on a number of electron donors and acceptors. In the A. ferrooxidans ATCC 23270 genome, computer analysis identified 11 genes encoding putative cytochromes c. At least eight putative cytochromes c were differentiated on gels in ATCC 33020 cells grown on ferrous iron or sulfur. All these cytochromes were associated with the inner or the outer membranes. Lower levels of total cytochromes c were observed in sulfur-than in ferrous iron-grown cells. One cytochrome c was specific for sulfur conditions while three were specific for iron conditions, suggesting that cytochrome c synthesis is modulated depending on the electron donor. ß
The acidophilic and strictly chemolithoautotrophic bacterium Acidithiobacillus
ferrooxidans oxidizes ferrous (Fe(II)) to ferric (Fe(III)) iron and reduced inorganic sulfur
compounds (RISC) to sulfuric acid, in oxic conditions. The redox proteins involved in the electron
transfer between Fe(II) and oxygen are encoded in the same transcriptional unit, the rus operon. The
expression of this operon is induced in the presence of Fe(II), but not Fe(III), and is not repressed in
the presence of sulfur (S0). A number of genes differentially expressed in iron or sulfur conditions
have been identified by microarrays transcript profiling. We show here that the presence of Fe(II)
induced the expression of the genes involved in iron oxidation and repressed the expression of the
genes involved in RISC oxidation. Identification of the regulator(s) involved in this transcriptional
regulation is underway. Two genes encoding putative regulators belonging to two transcriptional
units located downstream from the rus operon have been cloned. One regulator with a putative ironsulfur
cluster belongs to the IscR family and the other belongs to the two component
sensor/regulator family. Expression of both genes is induced in the presence of Fe(II) and is not
repressed by S0. The recombinant proteins have been purified and gel shift assays with the target
regulatory regions are in progress.
A high-molecular-weight c-type cytochrome, Cyc2, and a putative 22-kDa c-type cytochrome were detected in the membrane fraction released during spheroplast formation from Acidithiobacillus ferrooxidans. This fraction was enriched in outer membrane components and devoid of cytoplasmic membrane markers. The genetics, as well as the subcellular localization of Cyc2 at the outer membrane level, therefore make it a prime candidate for the initial electron acceptor in the respiratory pathway between ferrous iron and oxygen.
The chemolithoautotrophic Gram-negative bacterium Acidithiobacillus ferrooxidans is versatile and can grow on a number of electron donors and acceptors. In the A. ferrooxidans ATCC 23270 genome, computer analysis identified 11 genes encoding putative cytochromes c. At least eight putative cytochromes c were differentiated on gels in ATCC 33020 cells grown on ferrous iron or sulfur. All these cytochromes were associated with the inner or the outer membranes. Lower levels of total cytochromes c were observed in sulfur- than in ferrous iron-grown cells. One cytochrome c was specific for sulfur conditions while three were specific for iron conditions, suggesting that cytochrome c synthesis is modulated depending on the electron donor.
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