The oxidative stress response in Rhodobacter
Final Report Abstract
All organisms, which live in the presence of oxygen are also exposed to reactive oxygen species that are either produced by their own metabolism or by environmental factors. Rhodobacter is a free-living bacterium, which rapidly adapts to environmental changes. As a bacteriochlorophyll containing phototrophic bacterium Rhodobacter has also to cope with the generation of singlet oxygen. We chose R. sphaeroides and R. capuslatus as model organisms to study the response to reactive oxygen species. One focus of our study was on the role of thioredoxins and of the glutaredoxin system in the bacterial oxidative stress response. We showed that thioredoxins in R. sphaeroides and R. capsulatus are important in this response but are differentially regulated. We unraveled that thioredoxins can affect the expression of genes by interacting to gyrase and consequently affecting DNA supercoiling. We also revealed an important role of the glutaredoxin system especially for glutathion synthase in the defense against ROS. Mutations in genes for components of this system result in up-regulation of other genes for protective systems. The response to hydrogen peroxide was analyzed at transcriptome level. In R. sphaeroides many genes change in expression in response to this stress but only a small number of these genes is under control of the known regulator OxyR. The catalase gene is under control of OxyR and we showed different activities and functions for the individual catalases of R. capsulatus and R. sphaeroides. Some of the OxyR dependent genes are not under direct control of this transcriptional regulator but rather respond to the altered redox potential in cells that lack OxyR and the activation of genes directly by OxyR. An important role for carotenoids in the defense against singlet oxygen was confirmed for R. sphaeroides. No significant influence of singlet oxygen on carotenoids was observed, however synthesis rates of about 60 cytoplasmic proteins changed in response to singlet oxygen. This response was in part dependent on the alternative sigma factor E, in part, however, independent. Furthermore we showed that the alternative sigma factor RpoHII activates most of the sigma E dependent genes and that genes of the glutaredoxin system are a major target of the singlet oxygen response. In addition to the alternative sigma factors small non-coding RNAs have an important role in the photooxidative stress response.
Publications
- (2003) Expression of the trxA gene for thioredoxin 1 in Rhodobacter sphaeroides during oxidative stress. Arch. Microbiol. 180:484-489
Li, K., Pasternak, C., Klug, G.
- (2003). Thioredoxin 2 is involved in oxidative stress defence and redox-dependent expression of photosynthesis genes in Rhodobacter capsulatus. Microbiology 149:419-430
Li, K., Härtig, E. and Klug, G.
- (2004) Detoxification of hydrogen peroxide and expression of catalase genes in Rhodobacter. Microbiology 150: 3451-3462
Zeller, T., Klug, G.
- (2004) The glutathion/glutaredoxin system in Rhodobacter capsulatus: part of a complex regulatory network controlling the defence against oxidative stress. J. Bacteriol. 186: 6800-6808
Li, K., Hein, S., Zou, W., Klug, G.
- (2004) Thioredoxin can influence gene expression by affecting gyrase activity. Nucleic Acids Res. 32: 4563-4575
Li, K., Pasternak, C., Härtig, E., Haberzettl, K., Maxwell, A., Klug, G.
- (2005) Photooxidative stress in Rhodobacter sphaeroides: protective role of carotenoids and expression of selected genes. Microbiology 151: 1927-1938
Glaeser, J., Klug, G.
- (2005) Transcriptome responses to hydrogen peroxide in the facultative photosynthetic bacterium Rhodobacter sphaeroides. J. Bacteriol. 187:7232-7241
Zeller, T., Moskvin, O., Li, K., Klug, G., Gomelsky, M.
- (2006) Expression of the trxC gene in Rhodobacter capsulatus is coordinately controlled by its own gene product, thioredoxin 2, and the OxyR transcriptional regulator. J. Bacteriol. 188: 7689-7695
Zeller, T., Li, K., Klug, G.
- (2006) Thioredoxins in bacteria: functions in oxidative stress response and regulation of thioredoxin genes. Naturwissenschaften 93: 259-266
Zeller, T., Klug, G.
- (2007) Adaptive responses to singlet oxygen generated stress in Rhodobacter. J. Proteom Res.: 6:2460-2471
Glaeser, J., Zubawa, M., Lottspeich, F., Klug, G.
- (2007) Regulation of hydrogen peroxide-dependent gene expression in Rhodobacter sphaeroides: Defining the OxyR regulon. J. Bacteriol. 189: 3784-3792
Zeller, T., Mraheil, M., Moskvin, O., Li, K., Gomelsky, M., Klug, G.
- (2007) The phrA gene of Rhodobacter sphaeroides encodes a photolyase and is regulated by singlet oxygen and peroxide in a E dependent manner. Microbiology 153: 1842-1852
Hendrischk, A.-K., Braatsch, S., Glaeser, J., Klug, G.
