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Differential expression of two bc₁ complexes in the strict acidophilic chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans suggests a model for their respective roles in iron or sulfur oxidation

Patrice Bruscella^1,

¹ CNRS, Institut de Biologie Structurale et de Microbiologie, Laboratoire de Chimie Bactérienne, 31 chemin Joseph Aiguier, 13402, Marseille Cedex 20, France
² Instituto de Ciencias BioMédicas, Faculty of Medicine, University of Chile, Santiago, Chile
³ Andres Bello University, Center for Bioinformatics and Genome Biology, Fundación Ciencias para la Vida and Millennium Institute for Fundamental and Applied Biology, Santiago, Chile

Correspondence
Violaine Bonnefoy
bonnefoy{at}ibsm.cnrs-mrs.fr

Three strains of the strict acidophilic chemolithoautotrophic Acidithiobacillus ferrooxidans, including the type strain ATCC 23270, contain a petIIABC gene cluster that encodes the three proteins, cytochrome c₁, cytochrome b and a Rieske protein, that constitute a bc₁ electron-transfer complex. RT-PCR and Northern blotting show that the petIIABC cluster is co-transcribed with cycA, encoding a cytochrome c belonging to the c₄ family, sdrA, encoding a putative short-chain dehydrogenase, and hip, encoding a high potential iron–sulfur protein, suggesting that the six genes constitute an operon, termed the petII operon. Previous results indicated that A. ferrooxidans contains a second pet operon, termed the petI operon, which contains a gene cluster that is similarly organized except that it lacks hip. Real-time PCR and Northern blot experiments demonstrate that petI is transcribed mainly in cells grown in medium containing iron, whereas petII is transcribed in cells grown in media containing sulfur or iron. Primer extension experiments revealed possible transcription initiation sites for the petI and petII operons. A model is presented in which petI is proposed to encode the bc₁ complex, functioning in the uphill flow of electrons from iron to NAD(P), whereas petII is suggested to be involved in electron transfer from sulfur (or formate) to oxygen (or ferric iron). A. ferrooxidans is the only organism, to date, to exhibit two functional bc₁ complexes.

Present address: Department of Microbiology and Molecular Genetics, University of Texas Medical School, 6431 Fannin St, Houston, TX 77030, USA.

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