title: Vacuolar respiration of nitrate coupled to energy conservation in filamentous Beggiatoaceae.
abstract: We show that the nitrate storing vacuole of the sulfide-oxidizing bacterium Candidatus Allobeggiatoa halophila has an electron transport chain (ETC), which generates a proton motive force (PMF) used for cellular energy conservation. Immunostaining by antibodies showed that cytochrome c oxidase, an ETC protein and a vacuolar ATPase are present in the vacuolar membrane and cytochrome c in the vacuolar lumen. The effect of different inhibitors on the vacuolar pH was studied by pH imaging. Inhibition of vacuolar ATPases and pyrophosphatases resulted in a pH decrease in the vacuole, showing that the proton gradient over the vacuolar membrane is used for ATP and pyrophosphate generation. Blockage of the ETC decreased the vacuolar PMF, indicating that the proton gradient is build up by an ETC. Furthermore, addition of nitrate resulted in an increase of the vacuolar PMF. Inhibition of nitrate reduction, led to a decreased PMF. Nitric oxide was detected in vacuoles of cells exposed to nitrate showing that nitrite, the product of nitrate reduction, is reduced inside the vacuole. These findings show consistently that nitrate respiration contributes to the high proton concentration within the vacuole and the PMF over the vacuolar membrane is actively used for energy conservation.
authors.affiliation: Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359, Bremen, Germany. mbeutler@bionsys.de
authors.forename: Martin
authors.initials: M
authors.lastname: Beutler
authors.forename: Jana
authors.initials: J
authors.lastname: Milucka
authors.forename: Susanne
authors.initials: S
authors.lastname: Hinck
authors.forename: Frank
authors.initials: F
authors.lastname: Schreiber
authors.forename: Jörg
authors.initials: J
authors.lastname: Brock
authors.forename: Marc
authors.initials: M
authors.lastname: Mussmann
authors.forename: Heide N
authors.initials: HN
authors.lastname: Schulz-Vogt
authors.forename: Dirk
authors.initials: D
authors.lastname: de Beer
mesh_terms: D011756:Diphosphates / Q000378:metabolism; D004579:Electron Transport; D004734:Energy Metabolism; D020563:Gammaproteobacteria / Q000201:enzymology / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism*; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism; D014617:Vacuoles / Q000201:enzymology / Q000378:metabolism*
chemical_list: D011756:Diphosphates; D009566:Nitrates; D025262:Vacuolar Proton-Translocating ATPases