PMID:19542282

Citation	Bekker, M, de Vries, S, Ter Beek, A, Hellingwerf, KJ and de Mattos, MJ (2009) Respiration of Escherichia coli can be fully uncoupled via the nonelectrogenic terminal cytochrome bd-II oxidase.J. Bacteriol. 191:5510-7
Abstract	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.
Links	PubMed Online version:10.1128/JB.00562-09
Keywords	Adenosine Triphosphate; Cytochrome b Group; Cytochromes; Electron Transport Chain Complex Proteins; Escherichia coli; Escherichia coli Proteins; Fermentation; Gene Deletion; Oxidoreductases; Oxygen Consumption
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Main Points of the Paper

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Materials and Methods Used

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Phenotype Annotations

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Species	Taxon ID	Strain	Gene (if known)	OMP	Phenotype	Details	Evidence	Notes
Escherichia coli		MB20	cyoB	increase in the reduction level of the ubiquinone pool	Metabolic Activity	total ubiquinone pool content remained unchanged.	Biochemical Assay	Figure 2
Escherichia coli		MB21	appB	decreased total content of the ubiquinone pool	Metabolic Activity	no change in the redox state of the ubiquinone pool compared to wt	Biochemical Assay	Figure 2
Escherichia coli		TBE016	appB	decreased specific respiration rate	Metabolic Activity	reduced 47% in fully aerobic conditions compared to wt	Biochemical Assay
Escherichia coli		TBE016	appB	decreased total content of ubiquinone pool	Metabolic Activity	down 3-fold	Biochemical Assay	Figure 2A
Escherichia coli		MB37	ΔcyoB ΔcydB ΔnuoB	no growth on succinate as a carbon source	Growth		Plating Assay
Escherichia coli		MB44	?cyoB cydB::kan ?nuoB ?appB	no growth on succinate as a carbon source	Growth		Plating Assay
Escherichia coli		MB44	?cyoB cydB::kan ?nuoB ?appB	absent respiratory activity	Growth		Plating Assay
Escherichia coli		MB44	?cyoB cydB::kan ?nuoB ?appB	absent homolactic fermentation	Growth	when grown under anaerobic conditions, the cells produced amounts of acetate and ethanol, characteristic of mixed fermentation	Plating Assay
Escherichia coli		MB44	?cyoB cydB::kan ?nuoB ?appB	absent homolactic fermentation	Growth	when grown under anaerobic conditions	Plating Assay
Escherichia coli		MB37	ΔcyoB ΔcydB ΔnuoB	increased acetate production	Metabolic Activity	growth in glucose-limited chemostat cultures	Biochemical Assay	Table 2
Escherichia coli		MB37	ΔcyoB ΔcydB ΔnuoB	increased acetate production	Metabolic Activity	growth in glucose-limited chemostat cultures	Biochemical Assay	Table 2
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Notes

• GO:0019646
• GO:0009055

References

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