A respiratory nitrate reductase active exclusively in resting spores of the obligate aerobeStreptomyces coelicolorA3(2)

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The Gram-positive aerobeStreptomyces coelicolorundergoes a complex life cycle including growth as vegetative hyphae and the production of aerial hyphae and spores. Little is known about how spores retain viability in the presence of oxygen; however, nothing is known about this process during anaerobiosis. Here, we demonstrate that one of the three respiratory nitrate reductases, Nar-1, synthesized byS. coelicoloris functional exclusively in spores. A tight coupling between nitrite production and the activity of the cytoplasmically oriented Nar-1 enzyme was demonstrated. No exogenous electron donor was required to drive nitrate reduction, which indicates that spore storage compounds are used as electron donors. Oxygen reversibly inhibited nitrate reduction by spores but not by spore extracts, suggesting that nitrate transport might be the target of oxygen inhibition. Nar-1 activity required node novoprotein synthesis indicating that Nar-1 is synthesized during sporulation and remains in a latently active state throughout the lifetime of the spore. Remarkably, the rates of oxygen and of nitrate reduction by wetted spores were comparable. Together, these findings suggest thatS. coelicolorspores have the potential to maintain a membrane potential using nitrate as an alternative electron acceptor.

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