Extracellular superoxide production by Enterococcus faecalis requires demethylmenaquinone and is attenuated by functional terminal quinol oxidases
Article first published online: 7 JUL 2008
Volume 42, Issue 3, pages 729–740, November 2001
How to Cite
Huycke, M. M., Moore, D., Joyce, W., Wise, P., Shepard, L., Kotake, Y. and Gilmore, M. S. (2001), Extracellular superoxide production by Enterococcus faecalis requires demethylmenaquinone and is attenuated by functional terminal quinol oxidases. Molecular Microbiology, 42: 729–740. doi: 10.1046/j.1365-2958.2001.02638.x
- Issue published online: 7 JUL 2008
- Article first published online: 7 JUL 2008
- Accepted 26 July, 2001.
The intestinal commensal bacterium, Enterococcus faecalis, is unusual among prokaryotic organisms in its ability to produce substantial extracellular superoxide. Transposon mutagenesis, allelic replacement, and electron spin resonance (ESR)-spin trapping showed that superoxide production and generation of derivative hydroxyl radical were dependent on membrane-associated demethylmenaquinone. Extracellular superoxide was generated through univalent reduction of oxygen by reduced demethylmenaquinone. Moreover, extracellular superoxide production was inhibited by exogenous haematin, an essential cofactor for cytochrome bd, and by fumarate, a substrate for fumarate reductase. As integral membrane quinol oxidases, cytochrome bd and fumarate reductase redox cycle demethylmenaquinone, and are necessary for aerobic and anaerobic respiration respectively. A rat model of intestinal colonization demonstrated that conditions exist in the mammalian intestinal tract that permit a mode of respiration for E. faecalis that results in the formation of hydroxyl radical. These results identify and characterize the mechanism by which E. faecalis generates extracellular free radicals.