奇异球菌属：氧化应激机制、辐射抗性机制及环境适应策略

GenusDeinococcus:

OxidativeStressMechanisms,RadiationResistanceMechanisms,andEnvironmentalAdaptationStrategies

Abstract:TheresearchinvestigateshowDeinococcusbacteriaadaptinextremeenvironmentsintermsofthebacteria'sresistanceagainstoxidativestress,methodsofdealingwithradiation,anditsoverallabilitytosurviveindifferentenvironmentsanditdoesthisbycomparingthesethingsinDeinococcusbacteria.Thespeciesselectedarethreerepresentativespeciesincludingradiation-resistantDesulfovibrioradiodurans,heat-resistanceDesulfovibriogeothermalis,anddesiccation-resistanceDesulfovibriodeserti.Molecularbiologicaltechnologyisusedtostudytheprotectiveproteins,DNArepairmechanisms,andcellularstructureofthesethreerepresentativespecies.Keyfindings:Conserve/specificmechanism:Mn-antioxidants,recA-DNA,HSPs/species-specific:heat-tolerantenzymesD.geothermalisandtrehalosebiosynthesisD.deserti.Thestudyshowshowthosebacteriamixcommonandspecialstrategiestosurviveradiation,oxygentrouble,runningoutofwater,andveryhottempsusinglayersofdefensewiththingslikemakingyuckyoxygenstuffgoaway,fixingDNAbreaksquickly,andhavingstrongbarrierslikeS-layerproteins.TheseadjustmentssupplyinformationabouttheboundariesoflifeandarealsousefulincertainsectorslikeenvironmentalremediationwhichcomprisesofutilizingD.radiodurans'suraniumprocessingskillstogetridofradioactivewaste,andbiotechnologythatincludesmakingindustrialenzymesoutofD.geothermalis'sheat-stableproteins.Thisstudydrawsattentiontobiomimeticsolutionsinmedicine,agriculture,spaceresearch,etcandknowledgegapsremainingforrepairmechanismsandbiofilmmechanism.

Keywords:Deinococcus,oxidativestress,radiationresistance,DNArepair,extremeenvironment

I.Introduction

(A)Background

1.DiversityofthegenusDeinococcus:

(1)Extremeresistancecharacteristicsofrepresentativestrains:

TheDeinococcusgenusincludestherealtoughguysofthebacterialworld,withsomespeciesthrivinginreallyextremeenvironments.Deinococcusradioduransisthemostradiationresistantorganism,itcansurviveradiationdosesthousandsoftimeshigherthanwouldkillaperson.Also,thecellscanrepairtheirDNAevenaftersevereradiationbyscientistshasbeennoticedbythescientists.Andanotherone,Deinococcusgeothermalis,isfoundinextremelyhotplaceslikereallyhotvolcanicspringthataresohotitcouldcookin.Atthesametime,Deinococcusdesertiisknownforsurvivingindrydeserts,wherethereisnowateranditsurvivesformonthswithoutanymoisture.Andhavethesamesurvivaltechniquesbuttheyhaveadaptedtotheirownspecialtraitsfortheirenvironment.Theiramazingtoughnesscomesfromspecialprotectiveproteins,reallygoodDNAfix-upsystems,andspecialcellstuff.Itwillteachthemabouthowfarlifecangoanditcanalsobeusedformedicine,cleaningtheEarth,andgoingtospace.Theircapacitytoendureconditionsdeadlytomostlifemakesthemappealingthingsforbiologyresearch.

(2)Researchsignificance:

Deinococcusbacteriawestudy,itrevealstoushowlifecangooninveryextremesituations.Scientistslearntheirspecialskills,thentheythinkofnewwaystomakedirtyplacescleanagain.e.g.,maybethesekindsofbacteriacouldcleanupradioactivewasteortoxicmetalsoutofwhereit'sbeenspilled.andtheycanresistradiationandbadsituations,sotheyarealsousedforspaceexperiments.Scientistscheckhowthesemicrobesurvivesoastocreatebettersafetyequipmentforastronautsonlongdurationspaceflights.andthenalsotheenzymesfromthesebacteriathatcouldmaybebeusedinmoreindustrytypesasfarastemperaturegoesorotherextremelyharshconditions.ToknowaboutDeinococcus,somethingcanbeappliedtoourlife,knowingthelimitwecanachievetomakelivinginEarthandalsotodeveloptechnologytoprotectandexplorespaceTheirspecialsurvivalwaysmighthavetheanswerstolotsofourbigproblems.

2.Associationbetweenoxidativestress(ROS)andradiationdamage:

Radiationposesathreattocellsbothdirectlyandindirectly(Ottetal.,2020).Itdamagescellsbycausingawidevarietyofdamage,butalsogeneratesreactiveoxygenspecieswhichdothesame.Whenhighenergyradiationreactswithwatermoleculesinsidelivingcells,itmakesthatinstabilityoxygen-containingthings,whichthenstrikeatandalterveryimportantcellparts.ReactiveOzoneMoleculesarelikethemolecularequivalentoflittlewreckingballssmashingDNAstrands,turningproteinintocharredbitsandblastingupcellswithrandomatomicbombs.Andthiskindofindirectdamageisgenerallyevenworsethantheharmcauseddirectlybytheradiation,mainlybecausetheradiationhasaffectedmanykindsofcellsatthesametime.

Sothere'sstillanoxidativestressfromlikethosereactivemoleculesandthoseDeinococcusstillhasthosereallyextremekindsofresistance.Superoxideradicalandhydrogenperoxidemoleculewillattackbacteria,whichwillmaketheshapeoftheproteinchange,anditcannotworkproperly.AndbreaktheirDNAstrandsandharmthelipidsthatformtheircellmembranes.Thisthreathasahardtimegettingoverbecauseitjustkeepsgoing-ifsomethingstartshappening,thatcancausemorereactiveoxygentobeformed,makingthecellsevenmorehurt.

Deinococcusspecieshavedevelopedallsortsofprotectionsfromthatsortofoxidativeassault.Theirantioxidantsystemislikeasquadofmolecularfiremenwhojumprightontodealwiththosebothersomeoxygensthathavebecomeallagitatedbeforetoomuchhappens.Thebacteriaholdontobignumbersofdefensivestuffthatseizeandholdontodangerousstuff.andalsotheyhavesomeeffectiverepairmechanismthatcanrepairtheoxidativedamageontheseproteinaswellasDNA.Understandhowtheselittlebugscantakesomuchburningandthatmightclueusintohowtoshieldpeoplefromradiationandmakenewwaystostopthebodyfromcookingitselfwithitsownfreeradicals.Thebacteria'sapproachestotheuniversalbiologicalproblemillustratenature'scleverwaysofcounteringenvironmentalhazards.

(B)Researchscope

ThispaperwilllookathowdifferentDeinococcusspeciesprotectthemselvesfromoxidativestressandradiationdamagewhilelivinginharshenvironments.Wewouldstudythreemainareasoftheirsurvivalmethodology.Nowlet'stalkabouthowtheyhandlethosepeskyoxygenmolecules-that'stheirantioxidantdefensesystem.OK.Sowewillgetintotheiruniquednarestorationmethodsthatrepairradiationharm.Thelastthingwewilllookatishowtheymakeadjustmentstoliveinsomereallyawfulplaceslikeextremelyhot/dryareasordealingwithtonsofstuffintheirenvironment.

Thestudywillcompare3extraordinaryDeinococcusspecies:D.radiodurans-radiation-resisting,D.geothermalis-livinginhotsprings,D.deserti-survivingindeserts.Studyingthewaytheylivetogetherandthecooltrickstheydosowecanlearnaboutthisreallytoughkindofbacteria.It”'llbefocusingontheirprotectiveproteins,theirDNArepairenzymes,andtheircellsthatsurviveconditionsthatkillmostlife.

Thiscanhelpusfindnewtechnologytocleanpollution,protectastronautsinspace,andmakeheatresistantindustrialenzyme.Tounderstandtheseultimatesurvivorstellsusaboutthelimitsoflifeandwayshumanitycanhandleitstrialsaswell.Thestudyistryingtoexplaincomplicatedbiologicalproceduresinaneasytocomprehendmannerandindicatepracticalbenefitsoftheinformation.

II.OxidativeStressMechanismsinDeinococcus

(A)SourcesandhazardsofROS

1.EndogenousROS:

（1）O2-·andH2O2producedbyD.radioduransmetabolism.

Deinococcusbacteriameetconsiderableoxidativestresscausedbyreactiveoxygenspeciesduringmetabolism(Qietal.,2020).InD.radiodurans,vitalcellularactivitiesalwaysmakesuperoxideradicalsandhydrogenperoxideasnormalbyproducts.Thesemoleculeshavereallyactiveoxygenstuffinthem,whichcanbeprettydamagingwhenit'sproteins,DNA,andcellwallsiftheydon'tknowhowtokeepthemaway.Superoxideradicalsareformedwhentheoxygenmoleculespickupadditionalelectronsaccidentallyduringtheprocessofgettingtheenergy.Hydrogenperoxideisreleasedthroughtheincompletechemicalreactionsthroughoutthecells.

（2）IncreasedoxidativepressureinD.geothermalisunderhightemperatures.

D.geothermalundergoesmoreoxystresswithheightemperature(Jungetal.,2020).Theheatmakesitworseatdoingitsownchemicalreactions,whichmakesitmakeextrabadoxygenbyproducts.Highertempsalsocausetheoneswealreadyhavetobemoredestructivebygivingthemabitmoreenergytogoaroundattackingcellparts.Thisisahardsettingforthemicrobetocontinuallykeepitselffromgettinghurtbutstilldothenecessarypartsofliving.

Thesetypesofdangersareevenworsebecausetheyarealwaysthereandtheymakelotsofdifferentthingshappenatonce.Unliketheoutsidedangerswhichcomeandgo,theproductsofmetabolismconstantlycauseoxidativestressfromwithinthecell.Reactivemoleculescanattackanythingbiologicalnearby,anddamageaccruesslowly.BothD.radioduransandD.geothermalispossessfairlycomplexantioxidantsystemsasmeansofmanagingthesesortsofinternalhazards.Thisspeakstohowlifelearnswaystocopewithdangersthatcomeaboutthankstoitsownmostbasicchemistry.Understandingthemmighthelpusdealwiththingslikeillnesscausedbytoomuchortoolittleoxidationandgrowingold.

2.ExogenousROS:

Deinococcusbacteriafacedangerousreactiveoxygenspecies(ROS)notjustfromtheirinternalprocesses,butalsofromharshexternalsourcesintheirenvironments.Onebigdangerthat'soutsideiswhenthesungivesoffultravioletlight.WhenUVlightconnectswithbacterialcells,itresultsindamagingROSparticlesthatcanharmDNAandproteins.AnotherchallengeisthehighmetalconcentrationfromthingslikedesertsoilswhereD.desertilive.ThesemetalslinkupwithoxygeninyourcellstomakehurtfulROS.

Desertenvironmentscontainuniqueconcerns-strongsunlightmixeswithmetal-richsoiltocreatecontinuousoxidativestress.D.d.Deserticanhavesomespecialwaystodealwithproblems.ItmakesprotectivepigmentsthatsoakupbadUVrayssotheydon'tgetintocellsandmakeROS.AndalsothebacteriaareabletoneutralizethatROSfrommetal,aswellasstoreup,orneutralizethosedangerousmetals.

OtherROScomesfromoutsidetheROSlikeindustrialpollutionandradionuclidesforsomeD'sBacteria'sresistancetotheseoutsiderisksmakecleaninguppollutedsitesbeneficial.DefensesagainstROSfromoutsideteamupwiththeonesalreadyinside,sotherearelotsofbarrierstokeepingthebadstuffatbay.Knowingwhytheycanstanduptothesesortsofenvironmentalstressesmightgiveusideasformakingbettersunscreens,cleaner-upstrategiesforpollution,andradiation-shieldingtechnologies.

(B)Antioxidantdefensesystem

1.CoreroleofMn²⁺:

（1）Mn-polyphosphatecomplexesinD.radiodurans.

DeinococcusradioduransprotectsitselffromradiationdamagebyusingMn-PolyphosphateComplexes,whicharepowerfulantioxidants(Farcietal.,2020).Andthemanganese-phospatecompoundscanbuildspecificstructuresallthroughthecell,waitingforanytimethesedangerousreactiveoxygencompoundsshowup,theywillbeneutralizedbythesestructures.Themanganeseioninthesecompoundsisabletoneutralizetheharmfuloxygenfreeradicalswithoutdamagingproteins,DNAandotherimportantcellularcomponents.

TheyareMn-polyphosphateComplexbutNOTnormalantioxidantenzyme.It'snotthatthereisanybreakdownofreactivemoleculesviasomechemicalprocess,butratherthatthereactivemoleculesimplyinterceptsandneutralizestheharmfulmaterialbeforeitcandoharm.Themanganeseionschangetheiroxidationstate,sotheyneutralizethethreats,andthentheygobacktotheiroriginalformandcanprotectonceagain.Sothisrecyclingabilitymakesthesystemveryefficient,soasmallamountofmanganesecangivecontinuousprotection.

Thisdefensesystemisremarkableforitsdurabilityandversatility.Manganesecomplexescontinuetobestableunderextremelyradiatedanddehydratedconditions,whichwoulddisablemostbiologicalantioxidants.Todefendeverypartofthecellatonce,asifbuildingafortresstowardoffoxidativestress.Knowinghowthosestraightforwardmetal-basedcomplexesworksowellasprotectorscouldhelpusfigureoutnewwaystoshieldthingsfromradiation,keepmealsfreshlonger,andmaybeeventreatpeoplewhohavesicknessesrelatedtooxygenmakingtheircellsill.thesystemshowhownaturecantakesomethingassimpleaschemistryandsolveverycomplexbiologyproblems.

（2）DifferencesinMn²⁺transportsystemsinD.geothermalis.

Deinococcusgeothermalishasformedaspecificwaytohandlemanganeseionsthat'sdifferentfromitscloserelatives.AndeverysingleDeinococcusspeciesusesmanganeseasawaytodefenditselffromoxidativestress.ButD.geothermalistakesthisonestepfurtherasitcontainsuniquetransportproteinswhichcarefullycontroltheamountofmanganesewithintheircells.Thesetransportsystemsbehavelikemoleculargates,lettingjustthecorrectamountofmanganeseinwhilekeepingouttoomuchthatcouldcauseharm.

Geothermalisofhightemperatureenvironment.Theirmanganesemanagementisextraimportantbecauseofthat.Hotconditionsspeedcreationofbadfreeradicalsthatdemandextramanganeseforaid.Buttherecanbedownsidestotoomuchmanganese.Itcanaffectothercellprocesses.Thiskindofbacteriahasatransportsystemthatisjustright,ittakesinenoughmanganesetofightofffreeradicalsbutitdoesnotinterferewiththenormalcellactivities.

Whenscientistsgettodiscoverthesetransportingsystemsneatforshowinghoworganismsdealwithextremeenvironment.AndtheproteinsinD.geothermalistocarrymanganesedoverywellunderaboilingtemperature.Mostproteinsdon'tdothatanymore.Itwouldbecoolifunderstandingthosechangescouldhelpusgetindustrytohavechemicalprocessesworkwithhighheattemperatures,orevenwaysthatwouldkeeplivinglifeformsfromgettingburnedtoohot.ThemanganesetransportsystemisonepieceofD.geothermalis'sfullsurvivalstrategyinitsroughsurroundings.

2.Antioxidantenzymes:

（1）SODandcatalaseinD.radiodurans.

Deinococcusradioduranscombatsharmfulreactiveoxygenspeciesthroughapowerfulenzymedefensesystemfeaturingsuperoxidedismutaseandcatalase(Maqbooletal.,2020).Theseenzymesworktogethertoneutralizedangerousoxygenmoleculesthatformduringradiationexposure.Superoxidedismutaseactsfirst,convertingsuperoxideradicalsintohydrogenperoxide.Thencatalasetakesover,breakingdownthehydrogenperoxideintoharmlesswaterandoxygenmoleculesbeforeitcandamagecellularcomponents.

Thisbacteriumkeepsalotandalotoftheseprotectiveenzymesaround,evenwheneverythingisfine,soitcangetgoingrightawaywhenradiationshowsup.enzymesworkhard,theyturnthousandsofbadmoleculesoutsideyourcellintogoodoneseverysecond.Theyworktogethertostopthebuild-upofreactiveoxygenspeciesthatcoulddoalotofdamagetoDNA,proteins,andcellmembranes.

Andthisparticularsystemworksevenwherenormalenzymeswouldnot,whichiswhyit'susefulbecauseitwouldstillbeworkinginreallybadconditions.thesuperoxidedismutasefromD.radioduransandcatalasefromD.radioduranswerestillactiveunderintensiveradiationanddehydrationTheenzymeshavealotofpowerwhichstopsthemfromgettinghurtbutalsoprotectsalltheothercellsparts.Thesoliddefenseallowsustomakesenseofhowthebacteriumlivesthroughthingsthatwouldkillofflotsofotherones.Wewillknowmuchmoreaboutnaturalantioxidantsystemsandcouldfindabetterwaytodefendagainstoxidativestressinmedicinesandotherthings.

（2）ThioredoxinredundancyinD.deserti.

TheharshariddesertclimateofDeinococcusdesertibringsitoxidizationstressandacleverwaytofightagainstthisisbycreatingquiteanunconventionalshield-usinglotsofcopiesofThioredoxinproteins.Thesethioredoxinproteinsarelikelittlemolecularrepairtoolsthatfixthedamagereactiveoxygenspeciesdoes.WhatmakesD.desertiexceptionalisthatitcanproducedifferentversionsofDdSPL1andDdSPL2,makingitsdefensesystemhavesomeredundancy.Ifwegetdamagedorcannotworkfor1thioredoxin,otherscandoit.

Thethioredoxinproteinspitchintoo,safeguardingandrepairingthosecrucialsulfurcomponentsofotherproteinsthatareparticularlysusceptibletogettingoxidized.Theymakesureproteinsworkrightevenifthebacteriaaresuperdryorseesuper-brightsunindeserts.Therearealotofcopiessothebacteriawillhavebackupwhenitneedsitmost.

andit'sbecauseofthisextrasecuritythatD.desertihasasturdydefensivesystemagainstdangerousreactiveoxygencompoundsthatarealwayspresent,bacteriaareabletosurvivethroughextremeconditionsbecauseithaslotsofproteinwiththesamejobthatcandoitforthebrokenoneifneeded.Scientistslookatthesethioredoxinproteinstolearnabouthowlivingthingsdealwithtoughplacesandhowwecanusethattohelpsickpeopleormakenewstuff.D.deserti'swayofkeepingmorethanonedefensiveoptionshowshowmakingstrongbiologicalsystemscanbelearnedfrom.

3.DNAprotectionproteins:

（1）DdrA/DdrBinD.radiodurans.

Inthisway,dengericoccusradioduransprotectsitsDNAfromradiationdamagethroughspecificproteinscalledDdrAandDdrBthatactasmoleculoarshields(Santosetal.,2017).Afteryougethitbythisradiation,theseproteinswillinstantlyhookontothecrackedDNA,stopanymoreharmfromhappening,andkeepitsafeandstillforwhenthefixjobcanstart.DdrAfocusesonprotectingsingle-strandedDNAendsfrombeingdegraded,meanwhileDdrBwrapstheDNAareawhichhasbeendamagewithproteincomplexandcreateasafeenvironmentforrepairsystemtowork.

Twoproteinsworkasateamlikedefense.whenradiationcausesDNAstrandbreakDdrAcomesfirstandgivesprotectioncaptoenditislikegivingprotectivetiptoshoelacetopreventfraying.DdrBnextgoestocoataroundthebrokenpieces,holdingtheminplaceforeasyaccessforrepairingmachines.Inthisway,cellsgetfastsafetyandbuildingsupportatonce,sotheycankeepsafefromreallybadradiationevenifitcanmakebigtrouble.

Andhere'satrulyastonishingthingtheproteinsareefficientandversatile.TheyrecognizeandassociatewithmanytypesofDNAharmandthusprotectagainstmanykindsofradiation-inducedbreaks:Itworksreallyfast,too.DdrAandDdrBgettothedamagespotsjustminutesaftertheradiationhits.TheycanstabilizetheDNAwhenitisbroken,andtheywillnothinderthenextstageofrepairwork.Thisislikeatrickofnatureforresistingradiation.LearningaboutthemmaybecouldcauseimprovementingeneticengineeringanddifferentwayfrompreventingDNAharminanyothercreatures:

（2）DpsproteinvariantsinD.geothermalis.

DeinococcusgeothermalisspeciescontainsanuniquevarietyofDpsproteinwhichactsasadgetsforitsDNAwhenitgetsreallyhotThistypeofproteinvariantcancreatekindofsafeguardingcasingaroundbacterialDNAtokeepitfrombeingdamagedbyextremelyhightemperaturesandover-excessivesoxidationactivity.TheDpsproteinofD.geothermalisisdifferentthanotherbacteriaasthetemperatureissoclosetoboilingandthemoleculestaysfunctionalandstable.

Andthisheat-resistantversionofDpsisworkingintwokeyways.First,createacoverforDNAandthenkeepawaytheharmfulchemicalstuffsfromreachingoutthegeneticsubstancefornotharmingitanddestroyingitSecond,itcansafelymaintaintheironatom,avoidingitsreactionwithoxygentogeneratetoxicradicals.Thewaytheproteinisstructuredletsitdobothoftheseprotectivethingsatthesametime,whichmakesitveryspecialforprotectingD.geothermalisinthewarmplaceswhereitlives.

ScientistshavebeenstudyingthisuniqueDpsproteintofindouthowitkeepsupitsstructureandfunctioninsuchhotweather.Itmightalsoinspirenewtypesofheat-resistantmaterialsorimprovehowwedothingsthatneedreallyhighheatinfactories.Thissingleproteindoingmanykindsofprotectionishownaturecanreallyfixtrickyproblems.CopyD_geothermalismayhelpusfindnewwaystoprotectbiologicalthingsormakespecialhelpersthatdowellintoughsituations.

III.RadiationResistanceMechanismsinDeinococcus

(A)Typesofradiationdamageandrepairrequirements

1.Directdamage:SimilarityofDNAbreaksinD.radioduransandD.deserti.

RadiationisdangerousbecauseitdamagestheDNAdirectly,breakingthestrandsofgeneticinformation,andbothDeinococcusradioduransandDeinococcusdesertifoundsimilarwayofhandlingthisseriousproblem.DNAmoleculesgetsnippedbyhigh-energyradiationbothstrandsofthedoublehelixjustlikescissorscutarope.Thissortofdamage,calleddouble-stranbdbreak,wouldcausealmosteverylivingbeingtodieoffsincecellscannotreadthedirectionsofgenetics.Butthese2DeinococcusspeciescanstillsurvivewhentheyhavehundredsofthosebreaksintheirDNA.

It'ssocoolhowbothD.radioduransandD.desertahaveittogetherwhendealingwithDNAdamage,likethey'rebestbuddieseventhoughtheyliveintotallydifferentsuperextremeplaces!AndboththesevarietiesofbacteriaknowrightoffwhentheyhaveabrokenDNA-theirrepairjobisstartedatonce.TheystopbrokenDNAendsfrommovingawayfromeachothersotherepaircanbeexact.Andjustasourcellsputthingsonholdwhendamagehappens,theypausedividingsorepairsystemscanworkonmakingthingsrightbeforethecellmakesacopyoftheDNA.

ScientistshavefoundoutthatbothtypesofspeciesmakespecialproteinstohelpkeepbrokenDNAinplacewhilerepairenzymesgoaheadanddotheirwork.Sothatitstopsgettingalljumbledtogetherwhenit'sallputtogether.Thekeydifferenceisjusthowquicklytheyrespond-D.radioduranspicksuponadoseofradiationdamageahairquickerthanD.deserti,D.desertihasgotitssystembettersuitedfordealingwiththedryingdamages.ButthewaytheydealwithdirectDNAbreaksisthesamesortofmechanismthatmakesthemsodamnradiationproof.

Thesecommonrepairmethodsmaybeusefultodoctorsstudyinghowtocurepeopleaftertheyhavebeenexposedtolotsofradiationortohelpmakenewwaystochangegenes.ThesebacteriakeepandrepairtheirDNAinextremeconditiongiveusmanylessonstoprotectthegeneticmaterialinthehardenvironment,likethenuclearaccidentsiteandspace.TheirnaturalwaystofixradiationdamagemightgiveusideasfornewtechtokeepandmendDNAinmedicineandbiotech.

2.Indirectdamage:ROS-mediatedproteinoxidation.

RadiationhasabignegativeeffectoncellsnotjustbecauseitdamagesDNAdirectly,butalsobecauseitmakessomethingcalled"reactiveoxygenspecies".Thesethingsgoafterproteinsinthecellandmesswiththem(Timmins&Moe,2016).Radiationbumpsintowatermoleculesinsidecellsandthatgivesrisetothosenasty-oxygen-relatedmoleculesandthesethengettochemicallytamperwithproteins,changingboththeshapeandthefunction.Thesamedamageismuchmoreharmfulbecauseithitsmostofyourbody'sfunctionsatonce.Lotsoftheessentialproteinsdon'tdotheirjobaswellwhenthere'sanoxidationreaction.Theoxidizedproteinsoftenclumptogether,formclumps,whichdisruptnormalcellfunctionsandmaybetoxic.

Deinococcusbacteriahavedevelopedquitesomeeffectivewaystodealwiththisproteindamage.Therearecertainenzymeswhichareconstantlylookingatallthecellsforoxidisedproteinsanddestroyingthembeforeitgetsachancetodoanymoreharm.Molecularchaperoneshelpwithrefoldingmessedupproteinsbackintotherightshapeifthatcanbedone.Bacteriaalsohavesystemsthatallowthemtoquicklyproducereplacementsforproteinswhenthedamageistoobadtofix.andtheseprotectionsmakeitsothatevenwhenalloftheseproteinsareallsortofbrokenup,theycanstillkeeponworking.

WhatmakesDeinococcusspecialisthattheycanfixtherepairsystemsoftheproteinsthemselves.Theyhavebackupsofkeyrepairenzymeswhichavoidoxidantdamage.Theyhavecellsthatprioritizewhichproteinstofixfirst,andthosetendtobetheonesweneedtolivefirst.Manylayersofprotectionmakeitpossibleforthemtosurvivethekindsofproteindestructionthatwouldbedeadlyforallbutafewotherorganisms.Thebacteriahaveanall-aroundwayofprotectingitsproteinsandrepairingthemwhendamagedandourwayofdealingwithoxidativestresscouldbebetter.Theymaygiveusideasonhowtodealwithoxidativestressandhelpusinthefieldofmedicineandbiotechnologywhenitcomestostressanddamagetocells.

(B)Keyrepairmechanisms

1.Homologousrecombinationrepair(HR):

（1）RecAphosphorylationregulationinD.radiodurans.

DeinococcusradioduranspossessesasophisticatedDNArepairsystemcenteredaroundtheRecAprotein,whichundergoesprecisechemicalmodificationstocontrolitsrepairactivity(Rajpurohitetal.,2016).Whenradiationdamagesthebacterium'sDNA,specialenzymesaddphosphategroupstoRecAmoleculesinaprocesscalledphosphorylation.Thismodificationactslikeamolecularswitch,activatingRecA'sabilitytosearchforandmatchDNAsequencesbetweenbrokenstrandsandintacttemplateswithinthecell.

PhosphorylatedRecAproteinaswell,whichitdoesvariousthingslike:SoitputsdamagedDNAstrandsnexttocleanonestohelpcopythegeneticinformationproperlyandfixit.TheproteinhelpsexchangethestrandsofDNAfromthosewithbreaksandthosethathavenot,sothecellcanusegoodDNAasamodeltorebuildit.Wedokeepgeneticintegrityevenifradiationbreaksthewholegenomeintoafewgazillionpieces.

Thesystemisreallyamazinginthatit'scontrolledwithhighaccuracybywayofphosphorylation.ThecellcanstartuporimmediatelyturnoffRecAwhentheDNAisn'tharmed,whichsaveso