Molecular analysis of oxygen toxicity in the obligate anaerobe Roseburia cecicola: Isolation of a compound that degrades DNA when exposed to oxygen
O'Connor, Lawrence Thomas
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https://hdl.handle.net/2142/20568
Description
Title
Molecular analysis of oxygen toxicity in the obligate anaerobe Roseburia cecicola: Isolation of a compound that degrades DNA when exposed to oxygen
Author(s)
O'Connor, Lawrence Thomas
Issue Date
1991
Department of Study
Microbiology
Discipline
Microbiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Microbiology
Language
eng
Abstract
Environmental and nutritional conditions influence the ability of microorganisms to colonize gastrointestinal habitats. My thesis research provides a basis for examining the ecological significance of one such environmental factor, oxygen, and its effect on microbial colonization of the mammalian gastrointestinal tract. Studies described here examine how oxygen affects a bacterium isolated from the mucosa of the murine cecum, Roseburia cecicola. This organism is a strict anaerobe whose growth is inhibited when exposed to oxygen.
Cells of R. cecicola exposed to air have partially degraded chromosomal DNA. DNA is degraded into progressively smaller fragments as cells are exposed to air for longer periods of time. The process by which DNA is degraded can not be inhibited by rifampicin or chloramphenicol.
Partial purification of the compound that degraded DNA indicated that it was not a protein, had an apparent molecular of 2800, and contained appreciable amounts of iron. In addition, it degraded DNA isolated from various sources, had optimum activity at a pH of 6-8, and required a reducing agent for activity.
The ability of this compound to degrade DNA could be inhibited by catalase, peroxidase, hydroxyl radical scavengers, and certain metal chelators. Superoxide dismutase, nonspecific proteinases, and heat did not inhibit its activity. These results suggested that certain oxygen radicals were being generated, specifically the hydroxyl radical, which has previously been demonstrated to be capable of degrading DNA. Electron paramagnetic resonance (EPR) and spin-trapping studies subsequently confirmed that hydroxyl radicals were generated by this compound.
The results of these studies suggest that oxygen radicals are generated within the cells of Roseburia cecicola when exposed to environments containing oxygen. Whether these oxygen radicals are responsible for the degradation of chromosomal DNA in vivo remains to be determined. The inability of the cell to remove these radicals may explain the cytotoxicity of oxygen for this strict anaerobe.
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