Respiration of Escherichia coli can be fully uncoupled via the nonelectrogenic terminal cytochrome bd-II oxidase.
The respiratory chain of Escherichia coli is usually considered a device to conserve energy via the generation of a proton motive force, which subsequently may drive ATP synthesis by the ATP synthetase. It is known that in this system a fixed amount of ATP per oxygen molecule reduced (P/O ratio) is not synthesized due to alternative NADH dehydrogenases and terminal oxidases with different proton pumping stoichiometries. Here we show that P/O ratios can vary much more than previously thought. First, we show that in wild-type E. coli cytochrome bo, cytochrome bd-I, and cytochrome bd-II are the major terminal oxidases; deletion of all of the genes encoding these enzymes results in a fermentative phenotype in the presence of oxygen. Second, we provide evidence that the electron flux through cytochrome bd-II oxidase is significant but does not contribute to the generation of a proton motive force. The kinetics support the view that this system is as an energy-independent system gives the cell metabolic flexibility by uncoupling catabolism from ATP synthesis under non-steady-state conditions. The nonelectrogenic nature of cytochrome bd-II oxidase implies that the respiratory chain can function in a fully uncoupled mode such that ATP synthesis occurs solely by substrate level phosphorylation. As a consequence, the yield with a carbon and energy source can vary five- to sevenfold depending on the electron flux distribution in the respiratory chain. A full understanding and control of this distribution open new avenues for optimization of biotechnological processes.
Bekker
M
M
Swammerdam Institute for Life Sciences, BioCentrum, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands. m.bekker@uva.nl
de Vries
S
S
Ter Beek
A
A
Hellingwerf
K J
KJ
de Mattos
M J Teixeira
MJ
D000255:Adenosine Triphosphate / Q000096:biosynthesis*; D003573:Cytochrome b Group / Q000235:genetics / Q000378:metabolism; D003580:Cytochromes / Q000235:genetics / Q000378:metabolism*; D045222:Electron Transport Chain Complex Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D005285:Fermentation; D017353:Gene Deletion; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D010101:Oxygen Consumption
D003573:Cytochrome b Group; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D029968:Escherichia coli Proteins; D000255:Adenosine Triphosphate; C017168:cytochrome bo, E coli; D010088:Oxidoreductases; C040077:cytochrome bd terminal oxidase complex, E coli