studies-on-the-respiratory-system-in-alkaliphilic-bacillus-a-proposed-new-respiratory-mechanism

B.Jochimsenetal.:Stetteriahydrogenophila83Extremophiles(1998)2:83–92©Springer-Verlag1998ORIGINALPAPERAkiraHigashibata·TaketomoFujiwaraYoshihiroFukumoriStudiesontherespiratorysysteminalkaliphilicBacillus;aproposednewrespiratorymechanismReceived:October31,1997/Accepted:December17,1997AbstractRespiratoryelectrontransfersystemsintwoalkaliphilicBacillusspecies,YN-1andYN-2000,werein-vestigated.Inthecyanide-sensitivepathwayoftheobligatealkaliphilicBacillusYN-1,theterminalenzymewasacaa3-typecytochromecoxidaseconstitutinguptojust10%ofthetotaloxygen-reducingactivity,while90%oftherespiratoryactivitywasduetocyanide-insensitive,nonproteinaceousmaterialwithamolecularweightof662.Theseresultswereconsistentwiththecyanide-tolerantgrowthofthebacterium.Themolecularandcatalyticpropertiesofthenonproteinaceousmaterialwerenotidenticalwiththoseofmenaquinonesextractedfromthebacterium.Furthermore,thenonproteinaceousmaterialwasalsofoundinthefacul-tativealkaliphilicBacillusYN-2000,whenthatbacteriumwascultivatedinalkalineconditions.Anewrespiratoryoxygen-reducingmechanismcomprisinganonproteina-ceouscomponentandacatalaseisproposedforthesealkaliphilicBacillusspecies.KeywordsAlkaliphile·Cytochromeoxidase·Cyanide-insensitiverespiratorysystem·Nonproteinaceousrespira-toryterminalcomponent·H2O2IntroductionManybacteria,yeasts,andfungiwiththeabilitytogrowinextremelyalkalineconditionshavebeenisolatedfromsoils,andhavebeendesignated“alkaliphiles.”Alkaliphilicmi-croorganismshaveanumberofpotentialapplications,sincesomeofthemproducealkaline-tolerantextracellularen-zymes,suchascellulasesandproteinases(HorikoshiandAkiba1982).Thesealkaliphileshavealsopresentedanumberofintriguingproblemsinregardtobioenergetics.ATPsynthesisinalkaliphiles,likethatinneutralophiles,isdrivenbytheprotonmotiveforcegeneratedbyacombinationofprotonpumpingandrespiration(Guffantietal.1981).Ontheotherhand,thealmostneutralcytoplasmicpHofalkaliphilicbacterialcellsisreportedtobemaintainedbytheeffectofNa�/H�-antiporters(KrulwichandGuffanti1989a,b).