nature

ARTICLENitricoxide-dependentanaerobicammoniumoxidationZiyeHu1,3,HansJ.C.T.Wessels2,TheovanAlen1,MikeS.M.Jetten1&BoranKartal1,4Nitricoxide(NO)hasimportantfunctionsinbiologyandatmosphericchemistryasatoxin,signalingmolecule,ozonedepletingagentandtheprecursorofthegreenhousegasnitrousoxide(N2O).AlthoughNOisapotentoxidant,andwasavailableonEarthearlierthanoxygen,itisunclearwhetherNOcanbeusedbymicroorganismsforgrowth.Anaerobicammonium-oxidizing(anammox)bacteriacouplenitritereductiontoammoniumoxidationwithNOandhydrazineasintermediates,andproduceN2andnitrate.Here,weshowthattheanammoxbacteriumKueneniastuttgartiensisisabletogrowintheabsenceofnitritebycouplingammoniumoxidationtoNOreduction,andproduceonlyN2.Underthesegrowthconditions,thetranscriptionofproteinsnecessaryforNOgenerationisdownregulated.OurworkhaspotentialimplicationsinthecontrolofN2OandNOemissionsfromnaturalandmanmadeecosystems,whereanammoxbacteriacontributesignificantlytoN2releasetotheatmosphere.WehypothesizethatmicrobialNO-dependentammoniumoxidationmayhaveexistedonearlyEarth.https://doi.org/10.1038/s41467-019-09268-wOPEN1DepartmentofMicrobiology,IWWR,RadboudUniversityNijmegen,Heyendaalseweg135,6525AJNijmegen,TheNetherlands.2TranslationalMetabolicLaboratory,DepartmentofLaboratoryMedicine,RadboudUniversityMedicalCenter,GeertGrooteplein-zuid10,6525GANijmegen,TheNetherlands.3Presentaddress:Sanquin,Plesmanlaan125,1066CXAmsterdam,TheNetherlands.4Presentaddress:MicrobialPhysiologyGroup,MaxPlanckInstituteforMarineMicrobiology,Celsiusstraße1,28359Bremen,Germany.CorrespondenceandrequestsformaterialsshouldbeaddressedtoB.K.(email:bkartal@mpi-bremen.de)NATURECOMMUNICATIONS|(2019)10:1244|https://doi.org/10.1038/s41467-019-09268-w|www.nature.com/naturecommunications11234567890():,;Nitricoxide(NO)isahighlyreactivemoleculethatplaysakeyroleinatmosphericchemistryasanozonedepletingagentandastheprecursorofthegreenhousegasnitrousoxide(N2O)1–3.InbiologyNOhasseveraldistinctfunctions:itisaverypotenttoxin,butalsoasignalingmoleculeandaninter