isolation-and-characterization-of-a-novel-facultatively-alkaliphilic-nitrobacter-species

AbstractFivestrainsoflithotrophic,nitrite-oxidizingbacteria(AN1-AN5)wereisolatedfromsedimentsofthreesodalakes(KunkurSteppe,Siberia;CraterLakeandLakeNakuru,Kenya)andfromasodasoil(KunkurSteppe,Siberia)afterenrichmentatpH10withnitriteassoleelectronsource.Morphologically,theisolatesresem-bledrepresentativesofthegenusNitrobacter.However,theydifferedfromrecognizedspeciesofthisgenusbythepresenceofanadditionalS-layerintheircellwallandbytheiruniquecapacitytogrowandoxidizenitriteunderhighlyalkalineconditions.TheinfluenceofpHongrowthofoneofthestrains(AN1)wasinvestigatedindetailbyusingnitrite-limitedcontinuouscultivation.Undersuchconditions,strainAN1wasabletogrowatabroadpHrangefrom6.5to10.2,withanoptimumat9.5.CellsgrownatpHhigherthan9exhibitedaclearshiftintheop-timaloperationofthenitrite-oxidizingsystemtowardsthealkalinepHregionwithrespecttobothreactionratesandtheaffinity.CellsgrownatneutralpHvaluesbehavedmorelikeneutrophilicNitrobacterspecies.Thesedatademon-stratedtheremarkablepotentialofthenewnitrite-oxidiz-ingbacteriaforadaptationtovaryingalkalineconditions.The16SrRNAgenesequencesofisolatesAN1,AN2,andAN4showedhighsimilarity(≥99.8%)toeachother,andtosequencesofNitrobacterstrainR6andofNitrobacterwinogradskyi.However,theDNA-DNAhomologyinhy-bridizationstudieswastoolowtoconsidertheseisolatesasnewstrains.Therefore,thenewisolatesfromthealka-linehabitatsaredescribedasanewspeciesofthegenusNitrobacter,N.alkalicus,onthebasisoftheirsubstantialmorphological,physiological,andgeneticdifferencesfromtherecognizedneutrophilicrepresentativesofthisgenus.KeywordsNitrobacter·Nitrite-oxidizingbacteria·pH·Alkalineenvironments·ContinuouscultureIntroductionChemolithotrophicnitrifyingbacteriaplayanimportantroleinbiologicalnitrogencyclingbyconvertingreducedinorganicnitrogencompoundstonitrate.Ammonium-andnitrite-oxidizingbacteriaareubiquitousinterrestrialandaquaticnaturalenvironmentswithmoderatecondi-tions(Bocketal.1992;LaanbroekandWoldendorp1995)andalsoinsomeman-madesystemssuchaswastewatertreatmentplant