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Transcriptome and Physiological Responses to Hydrogen Peroxide of the Facultatively Phototrophic Bacterium Rhodobacter sphaeroides

Tanja Zeller,^1, Oleg V. Moskvin,^2, Kuanyu Li,¹ Gabriele Klug,^1* and Mark Gomelsky^2*

Institut für Mikrobiologie und Molekularbiologie, University of Giessen, Giessen, Germany,¹ Department of Molecular Biology, University of Wyoming, Laramie, Wyoming²

Received 22 April 2005/ Accepted 22 July 2005

The transcriptome responses to hydrogen peroxide, H₂O₂, of the facultatively phototrophic bacterium Rhodobacter sphaeroides grown under semiaerobic conditions were investigated. At 7 min after the addition of 1 mM H₂O₂, the expression of approximately 9% of all genes (total, 394) was changed reliably by at least twofold. At 30 min, the number of genes (total, 88) and the magnitude of expression changes were much lower, indicating rapid recovery from stress. Two types of responses were observed: (i) an H₂O₂ stress response per se and (ii) a shift to high-oxygen metabolism. The former response involved the upregulation of genes for H₂O₂ detoxification, protein folding and proteolysis, DNA damage repair, iron transport and storage, iron-sulfur cluster repair, and the downregulation of genes for protein translation, motility, and cell wall and lipopolysaccharide synthesis. The shift to high-oxygen metabolism was evident from the differential regulation of genes for aerobic electron transport chain components and the downregulation of tetrapyrrole biosynthesis and photosystem genes. The abundance of photosynthetic complexes was decreased upon prolonged exposure of R. sphaeroides to H₂O₂, thus confirming the physiological significance of the transcriptome data. The regulatory pathways mediating the shift to high-oxygen metabolism were investigated. They involved the anaerobic activator FnrL and the antirepressor-repressor AppA-PpsR system. The transcription of FnrL-dependent genes was down at 7 min, apparently due to the transient inactivation by H₂O₂ of the iron-sulfur cluster of FnrL. The transcription of the AppA-PpsR-dependent genes was down at 30 min, apparently due to the significant decrease in appA mRNA.

Supplemental material for this article may be found at http://jb.asm.org/.

T.Z. and O.V.M. contributed equally to this work.

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