!!!adaptive-modifications-in-membranes-of-halotolerant-and-halophilic-microorganisms

JournalofBioenergeticsandBiomembranes,Vol.21,No.1,1989MINI-REVIEWAdaptiveModificationsinMembranesofHalotolerantandHalophilicMicroorganismsNicholasJ.Russell~ReceivedAugust17,1988AbstractHalotolerantandhalophilicmicroorganismscangrowin(hyper)salineenvi-ronments,butonlyhalophilesspecificallyrequiresalt.Genotypicandphenotypicadaptationsaredisplayedbyhalophiles;thehalotolerantsadaptphenotypically,butitisnotestablishedwhethertheyshowgenotypicadapta-tion.Thispaperreviewsthevariousstrategiesofhaloadaptationofmembraneproteinsandlipidsbyhalotolerantandhalophilicmicroorganisms.Moderatehatophilesandhalotolerantsadapttheirmembranelipidcompositionbyincreasingtheproportionofanioniclipids,oftenphosphatidylglyceroland/orglycolipids,whichinthemoderatelyhalophilicbacteriumVibriocosticolaappearstobepartofanosmoregulatoryresponsetominimizemembranestressathighsalinities.ExtremehalophilespossesstypicalarchaebacteriaIetherlipids,whicharegenotypicallyadaptedbyhavingadditionalsub-stitutionswithnegatively-chargedresiduessuchassulfate.Incontrasttothelipids,itislessclearwhethermembraneproteinsarehaloadapted,althoughtheymaybemoreacidic;veryfewdependonsaltfortheiractivity.KeyWords:Halotolerant,microorganisms;halophiIe,microbial;membrane,lipidsandsalinity;lipidcomposition,microbialandsalinity;salinity,effectsonmicrobialmembranes;osmoticpressure,effectsonmembranelipids;bacteria,halotolerantandhalophilic;phenotypicadaptationofmicrobialmembranestosalt.HalotolerantandHalophilicMicroorganismsMicroorganismsarewellknownfortheirabilitytooccupyawidevarietyofenvironmentalniches,bothnaturalandman-made,andthesalineenvironmentIDepartmentofBiochemistry,UniversityofWalesCardiff',P.O.Box903,CardiffCF1IST,Wales,U.K.930145-479x/89/0200-0093s06.00/0~1989PlenumPublishingCorporation94Russellprovidesawell-recognizedexampleofsuchanenvironment--oftencalledextreme,althoughthistermismisleadingasexplainedbelow.Adistinctionmustbemadebetweentoleranceforsaltandrequire-mentforsalt(Larsen,1986).Halotolerantmicroorganismshavenosp