Affiliation:
1. Institut für Mikrobiologie und Molekularbiologie, University of Giessen, Giessen, Germany
2. Department of Molecular Biology, University of Wyoming, Laramie, Wyoming
Abstract
ABSTRACT
The transcriptome responses to hydrogen peroxide, H
2
O
2
, of the facultatively phototrophic bacterium
Rhodobacter sphaeroides
grown under semiaerobic conditions were investigated. At 7 min after the addition of 1 mM H
2
O
2
, 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 H
2
O
2
stress response per se and (ii) a shift to high-oxygen metabolism. The former response involved the upregulation of genes for H
2
O
2
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 H
2
O
2
, 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 H
2
O
2
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.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology