Molecular oxygen (O2) is critical to life on this planet; it is a product of oxygenic photosynthesis and it is a substrate for bioenergetic pathways like aerobic respiration. While O2 is relatively inert, it is converted to different chemical classes of toxic reactive oxygen species by either one electron transfer or energy transfer reactions. When single electrons are transferred to O2, it is reduced to superoxide, hydrogen peroxide, or hydroxyl radicals. When energy is transferred to O2, singlet oxygen ([1]O2) is formed. We have considerable information about how cells respond to superoxide, hydrogen peroxide and hydroxyl radicals. However, relatively little is known about how cells respond to [1]O2, a common reactive oxygen species that can destroy the integrity of bioenergetic membranes, damage many biomolecules, generate mutations, or kill cells. To rectify this situation, we will study the bacterial response to [1]O2. Our experiments capitalize on what is known about the formation and response to conditions that generate [1]O2 in the alpha-proteobacterium Rhodobacter sphaeroides. This is the biological system of choice for studying this response since photosynthetic organisms like R. sphaeroides generate significant amounts of [1]O2 as a byproduct of solar energy capture. In addition, we have identified a transcriptional response to conditions that generate [1]O2 in this bacterium. This transcriptional response to [1]O2 depends on an alternative sigma factor in the extracytoplasmic function family, sigmaE, and the anti-sigma factor, ChrR. We have also obtained a 3-dimensional view of the sigmaE-ChrR complex that controls the transcriptional response to [1]O2. In this project, we will determine how the presence of [1]O2 increases sigmaE activity. [1]O2 is bacteriocidal to cells lacking sigmaE, so we will also identify gene products that protect cells from this toxic reactive oxygen species. The chemical properties of [1]O2 predict that the damage generated by this reactive oxygen species and the activities that function in this stress response will differ from those produced in the presence of superoxide, hydrogen peroxide or hydroxyl radicals. Analysis of microbial genome sequences indicates that homologs of R. sphaeroides sigmaE and ChrR are present in many photosynthetic bacteria plus non-photosynthetic bacteria that are likely to encounter [1]O2 generated by other pathways as part of plant and animal defenses against pathogenic microbes. Thus, our research will answer important questions about the ability of many cells to sense and protect themselves from [1]O2 and the nature of the modifications caused by [1]O2 to proteins and other biomolecules. The use of [1]O2 by eukaryotic cells to defend against pathogenic microbes and in photodynamic therapy to kill cancer cells predicts that our findings will have large antimicrobial and therapeutic potential. ? ? ?

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
Project #
Application #
Study Section
Prokaryotic Cell and Molecular Biology Study Section (PCMB)
Program Officer
Anderson, James J
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Wisconsin Madison
Schools of Earth Sciences/Natur
United States
Zip Code
Lemke, Rachelle A S; Peterson, Amelia C; Ziegelhoffer, Eva C et al. (2014) Synthesis and scavenging role of furan fatty acids. Proc Natl Acad Sci U S A 111:E3450-7
Nam, Tae-Wook; Ziegelhoffer, Eva C; Lemke, Rachelle A S et al. (2013) Proteins needed to activate a transcriptional response to the reactive oxygen species singlet oxygen. MBio 4:e00541-12
Dufour, Yann S; Donohue, Timothy J (2012) Signal correlations in ecological niches can shape the organization and evolution of bacterial gene regulatory networks. Adv Microb Physiol 61:1-36
Kim, Min-Sik; Dufour, Yann S; Yoo, Ji Sun et al. (2012) Conservation of thiol-oxidative stress responses regulated by SigR orthologues in actinomycetes. Mol Microbiol 85:326-44
Dufour, Yann S; Imam, Saheed; Koo, Byoung-Mo et al. (2012) Convergence of the transcriptional responses to heat shock and singlet oxygen stresses. PLoS Genet 8:e1002929
Greenwell, Roger; Nam, Tae-Wook; Donohue, Timothy J (2011) Features of Rhodobacter sphaeroides ChrR required for stimuli to promote the dissociation of ?(E)/ChrR complexes. J Mol Biol 407:477-91
Dufour, Yann S; Kiley, Patricia J; Donohue, Timothy J (2010) Reconstruction of the core and extended regulons of global transcription factors. PLoS Genet 6:e1001027
Dufour, Yann S; Wesenberg, Gary E; Tritt, Andrew J et al. (2010) chipD: a web tool to design oligonucleotide probes for high-density tiling arrays. Nucleic Acids Res 38:W321-5
Wang, Yanling; Dufour, Yann S; Carlson, Hans K et al. (2010) H-NOX-mediated nitric oxide sensing modulates symbiotic colonization by Vibrio fischeri. Proc Natl Acad Sci U S A 107:8375-80
Donohue, Timothy J (2009) Targeted sigma factor turnover inserts negative control into a positive feedback loop. Mol Microbiol 73:747-50

Showing the most recent 10 out of 22 publications