Bacterial Reproduction.pdf

This PowerPoint wants to explore the bird's eye view of the reproduction of bacteria in general and the genetic recombination of bacteria in particular.

1. A Presentation by
Dr. N. Sannigrahi,
Associate Professor,
Department of Botany,
Nistarini college, Purulia
( NAAC Accredited ‘A” Grade)
D.B. Road, Purulia (W.B)
723101, India

3. Unicellularorganismsdonotundergoreproductionlikethemulticellular
oneandthestoryoftheprokaryotesquitedifferentfromtherestneitherin
modenorinthecomplexity.Reproductioninbacteriaissimplythe
multiplicationinnumbereitherbyvegetativeandasexualmethod.Thereis
nosexualreproductionneitherbytheformationofsexorgan'sfollowedby
thegametesnorbythefusionofthenon-identicalgamets.Butinsome
cases,objectiveofusualreproductionforthereassortmentofthegenes
takesplacebutthisprocessisquitedissimilarfromtherest.Mainlythree
typesofreproductionnoted:
Vegetativemethod-Onlybythecellitselfwithoutanykindof
specialization
Asexualmethod-Cellundergonemodificationbythedintofsome
specializedstructuretoaddresstheharshenvironment
Sexualmethod-thisisnottrulysexualoneduetolackofdesirable
specialization,ratheritistheprocessoftherecombinationofgenesinthe
truesense.

4. The vegetative method mostly executed by the decisive use of the body cell
followed by a certain degree of modification. It occurs by three methods-
Budding,
Fragmentation,
Binary fission.
BUDDING:
a. small protuberance called bud at one end of the cell forms,
b. Genome replication occurs and copy of the replicated genome enters into
the bud,
c. The bud undergoes enlargement and finally the bud gets separated from
the parent cell
d. The bud gives the formation of new cell.

5. FRAGMENTATION
Duringunfavorablecondition,protoplasmundergoescompartmentalization
formingminutebodiescalledgonidia,
Eachgonidiumnowgrowstoanewbacteriumunderfavorablecondition,
Priortotheformationofgonidium,genomeundergoesreplicationto
increasetheDNAcontent.
BINARYFISSION
Thecellcontentsbecomedoubled,
DNAreplicationoccurs,DNAundergoespartitionandcrosswall
formationtakesplace,
Bacterialchromosomegetsattachedtothecellmembraneandreplicated
intotwo,
ThedaughterDNAstillattachedtothecellwallandgetseparatedbya
simplepinchingoffprocess,

7. Acrosswallisformed.Thetransverseplasmamembraneislaiddown
followedbythecentripetalgrowthofthecellwallandsplitstheplasma
membraneintotwohalves.
Thegoodenvironmentalconditionfavorsthisprocessand20-30minutes
areenoughtomultiplythecell,
Thebinaryfissionenablesthebacteriatomultiplyingeometricprogression
toformabigbacterialcolonywithinashortspan.
ThelargegroupofbacteriacalledActinomycetesformbranchinghyphae;
sporesdevelop,singlyorchain,fromthetipsofthesehyphaeby
crosswall.Iftheyenclosedinsaccalledsporangiosporesandifnottheyare
calledconidiophores.Veryoften,cyst,thickwalleddesiccationresistant
formsdevelopbythedifferentiationofvegetativecellsandgerminate
undersuitableconditionsasapartofreproduction.

8. Duringunfavorablecondition,thebacteriaundergoesasexualprocessof
reproductionandthisisenabledbytheformationofendosporebythe
followingmethods:Apertoftheprotoplastbecomesconcentratedaround
thegenome,
Ahardresistantwallisformedaroundit,therestofthebacterialcell
undergoesdegeneration,
Eachendosporeiseitherspherical,orcylindricalorellipsoidalinshape,
Endosporeisarestingsporeundergoesanumberofmodification.The
outerlayeristhin,delicatecalled–exosporium,followedbythesporecoat.
Innertosporecoat,thecortexcontainsconcentricringsofwall.Belowthe
cortex,thecorecellwallisencirclingthecellmembraneandprotoplasm,

10. Underfavorablecondition,theendosporegerminatesbyimbibingwater,
activatingthecytoplasm,synthesizingmetabolitesandswellingfollows
theburstingofwallgivingrisetotheformationofnewvegetativecell.
TheendosporeconsistsofthebacterialDNA,ribosomeandlarge
amountsofdipicolinicacid.Dipicolinicacidisaspore-specificchemical
thatappearstohelpintheabilityforendosporestomaintaindormancy.
Thischemicalaccountsforupto10%-15%ofthespore'sdryweight.It
occursincombinationwithlargeamountsofcalciumandprobablylocated
inthecorei.e.inthecentralpartofthespore.Thecalcium-DPAcomplex
possiblyplayavitalroleintheheatresistanceofendospores.Synthesisof
DPAandtheuptakeofcalciumoccursduringadvancestagesof
sporulation.

11. Geneticrecombinationisamostdramaticepisodeinbiologicaldramathat
enablestwogenetictraitsoftwonon-identicalcellscometogetherand
recombineinamannerandmaketheavenueoftheformationofthe3
rd
cell
i.e.zygotetogivethebirthofnewindividual.Itisoneofthemost
interestingbiologicalprocessthatactsexpeditethebiologicalevolution
process.Theprocessofthegeneticrecombinationinprokaryotesunlike
differentfromtheeukaryotes.Inbacteria,thesexualreproductiontruly
absentbutgeneticrecombinationstillprevailsasanaturaladaptationfor
thenewcombinationofgenes.Ifthefavorablenewcharacterisgenerated
bymutation,itspreadstothesuccessorsthroughthisgenetic
recombination.Inbacteria,thisprocessofmixingofgenestakeplace
mostlybythreemethods-Conjugation,transformation&transduction.
GENETICRESHUFFLING:Itenablestheproductionoftraitsthatdiffer
fromtheoriginalparent,
onlytheexogenotefromthedonoristransferredtorecipienttoenable
variation.

12. Comparativegenomicanalysisofcloselyrelatedmicroorganismsthat
exhibitdifferentphenotypeshaverevealeddistinctgenomicdifferences.
Often,theseidiosyncraticdifferencesresultfromhorizontalgenetransfer,
themovementgenesthatarenotdirectdescendentsfromoneanother.
Thesehorizontalgenetransfersallowscellstoquicklyacquirenew
charactersanddrivesmetabolicdiversity.
Conjugation-transferofgeneticmaterialoccurthroughdirectcontact
betweenthetwocells;donorandrecipient
Transformation-Theexogenate(portionofthegeneticcomplementofthe
donor)istakenupbytherecipientfromthesurroundingmedium,
Transduction-Thetransferofageneticmaterialsoccurfromonecellto
otherbybacteriophageorbyavirus.

14. Thegenomeoftherecipientiscalledendogenoteandtheincomplete
zygoteisformedinthisattributeiscalledpartialdiploidormerozygote.
TransferoffreeDNAreleasedfromadonorbacteriumtorecipient
bacteriumthroughtheliquidmediuminwhichtheygrow,
Doesnotrequirelivingbacteriacell,onlyrequiresDNAinthe
environment,
TransferDNAregionsfrom1-10kilobasesofDNA,
AKindofgenetictransformationwasdiscoveredbyF.Griffith(1928)on
theepochmakingachievement.Theexperimentwasconductedofthetwo
strainsofStreptococcuspneumoniae(Pneumococcouspneumoniae);One
wasvirulent,(pathogenic)capsulated,smoothform(S)andotherwas
avirulent,non-pathogenic,non-virulent(non-pathogenic)rough(R).The
experimentdesignedasfollows:Virulentstrain(S)–injectedintomice-mice
dead
Avirulentstrain®–injectedintomice-micelives
Heatkilledvirulent(S)-injectedintomice-micelives
Heatkilledvirulent(S)+livingvirulent®-injectedintomice-micedead.
IsolatedStypestrainfromthedeadmicefromthelastexperiment.

16. TheVirulentandavirulentcharacterswerenothingbutthepresenceof
genepresentthereafter.
Thevirulentstrainresponsibleforthedeathofthemicebutwhenitwas
heatedandinjected,theeffectofthegenedidnotproduceanyoutcome.
Butwhentheheatkilledvirulentstraintreatedwithlivingavirulent,the
transformationoftheavirulenttovirulentonetakesthatcausedthedeath
ofthemice.
Initially,Griffiththoughtthevirulenceduetothepolysaccharidepresentin
thecapsulebutlateron,theexperimentconductedbyO.T.Avery,Mac
Leod&McCarty(1944)confirmedthetransformingprinciplewasnone
butDNA,notpolysaccharidepresentinthecapsule.Thusresearchopena
newnovelavenueofgeneticresearchinthemicrobiologicalfield.
HeattreatedS+R=Micedeath,Deathmice-Stype+R-type(Isolated
bacteria)
Dnase+heattreatedS+R=Alive
Protease+heattreatedS+R=Death

18. Competenceistheprocessthatenablesthecelltoincorporatetheforeign
DNA,
ThedonorDNAbindstothecellsurfacebytheDNAbindingproteininsidethe
recipientcell,
EitherdsDNAorssDNAentersintotherecipientcell,
Theendonucleaseenzymedegradesoneofthestrandandallowsthe
incorporation,ligaseenzymefilledupthegap,
AllbacteriainthemediumcontainingdonorDNA(exogenote)arenotcapable
oftransformation,onlythecompetentcanhavethepleasureofthis
transformation.Buttheabilityoftransformationcanbeinducedbycertain
methods.Onthebasisoftheabilityoftransformation,itcanbedividedinto
twotypes
Naturaltransformation-Bacteriaencodedwiththecompetencyfactorintheir
genomelikemostlyGram(+)bacterialikeS.pneumoniae,Bacillussubtilisetc,
ArtificialTransformation-Theartificialtransformationcanbeinducedinthe
non-competentbacteriabytheadditionofcationslikeCaorRubidiumchloride
orelectroporationbyheatshockinthemediumlikemostGram(-)negative
bacteria,Azetobacteragilusetc.

19. Akindofgenetictransformationbywhichtwosexuallydifferentiated
bacterialcells–donorandrecipienthavethepleasureofit.Aconsiderable
segmentofdonorgeneticmaterialistransferredtotherecipientcells
whichmayundergorecombinationwiththecorresponding(homologous)
segmentsoftherecipientgeneticmaterials.ThesegmentsofDNAmaybe
largeroneincomparisontotheothertwomethodsofrecombination.
AccordingtoHayes(1952),conjugationisaheterothallicsysteminwhich
recombinationismediatedbyonewaytransferofgeneticmaterialfromthe
donortorecipientbacterialcellthroughtheconjugationtubeLetusexplore
thebeautyofthisdramaundertwoheadings
DonorandSexfactor,
Processofconjugation&Sexduction.

20. Donorstateisattributedbythepresenceofgeneanditmightbeinfectious
vector(Hayes,1953)inthedonorcells.ItistermedasConjugons(Luria,
1963)andconjuganstermedasepisomes.EpisomesarecytoplasmicDNA
elementshavingcapacitytointegratewiththebacterialchromosome.
DonorstateiscalledfertilityfactororFfactorlikeotherfactorsRtf,col
etc.WhenabacteriumcontainsFfactorcalledF+asmaleandtherecipient
asF(-).F+andHfrarebasicallybutthelatercantransferlargesegmentsof
genome.BothF+andHfrarecharacterizedbythepresenceofflagellum
likestructureonthecellsurfacecalledsexpilus.Thesexfactorsperform
thefollowingfunctions:
Determinethedonorstate,Helpinthesynthesisofsurfaceantigen,
Mobilizethegeneticmaterialtransfer
Provideenenergyduringtheprocess

21. F+andF-Conjugation
ThisisthemostnormalwhentheFfactoristransferredbutnotthe
bacterialgenome,
ItconvertstherecipientstoF+,
ThecirculardsDNAoftheFfactorisnickedononeofthestrand,
Thestrandpassesasasinglestrandintotherecipientcellandsynthesize
thecomplementarystrandandcircularizesintotherecipientcell,
ThedonordsDNAalsoregainthenormalsatebyfollowingusing
replicationpattern,
ThenickismadeatthesitecalledOriT(originoftransfer)andthe
replicationoccursbyrollingcirclemechanisms.

22. HfrandF-conjugation
HfrisastrainwheretheFfactorisintegratedwiththebacterial
chromosome.Thisintegrationisduetocrossingoverbetweentheregions
ofhomologyofsharedbytheplasmidsandthebacterialgenome.The
homologoussequenceofDNAinthebacterialchromosomearecalled
insertionsequences.
WhentheHfrstraincomesincontactwithF-strain,replicationtransfer
beginswithFplasmidregionatOriTsiteandcontinuesintothe
chromosomalregionsofthebacterialgenome.
ThetransferstartsfromthecutregionandthebacterialDNAistransferred
throughtheconjugationtubekeepingtheFfactoratitsrearend,
IftheentireDNAalongwithFfactoristransferred,itbecomesHfrbut
onlybacterialgenometransfers,itbecomeF-

24. Thespecificpairingoccursbythespecificflagellumcalledsexpilus
presentinbothHfrandF-cellswhichhasaholeof2.5µmdiameter
throughwhichthetransferofgeneticmaterialtransfertakesplace.
Recombinationoccursonlyathomologouspoints
Specificpairingofthetwostrainsaredesired
Transferofgeneticmaterialfromdonortorecipient,
Geneticrecombinationbetweendonorandrecipientcell,
Expressionofnewphenotypeintherecipientcellisobligatory.
TransferofplasmidDNAisefficientandrapid;underfavorableconditions
virtuallyeveryrecipientcellspairswithadonoracquiresaplasmid.
TransferofFplasmidhaving100KbpofDNAtakesabout5minutes.

25. ItisakindofconjugationbetweenF`(Prime)andF-cells,
ThemalebacteriacalledF`,andF`cellshaveFfactorwithsomegenesof
thebacterialgenomeinit,
F`cellsoriginatefromHfrstrain.WeknowthatHfrisformedbythe
integrationwithbacterialchromosome.Butattimesofintegrationreverts
duringwhichtheFfactorbringssomeportionofthebacterialgenomein
exchangeofitsownorevennot.ThustheFfactorhassomegenesofthe
bacterialchromosomeandbecomesF`,
DuringconjugationbetweenF`andF-cells,theF`factoristransferredto
therecipientF-cells.Therecipientcellbecomesaheterozygousforthe
portionofgenespresentintheF`factor.Geneticrecombinationtakes
place.ThegeneticrecombinationmediatedbyF`factorcalledsexduction
asidentifiedbyAdelbergandBurns(1956).

26. Anuniquetypeofgeneticrecombinationwheregenesofonebacteria
transferredtoanotherbymeansofbacteriophages,avector.Thevirusofthe
bacteriophagehavetheexcitementofthetransferiscalledtransducingphage.
ThisuniquetypeofgenetransferwasdiscoveredbyZinderandLederberg
(1952)onSalmonellatyphimurium.
Theoverallprocessisasfollowed:Here,thebacteriophageacquiresaportion
ofbacterialDNAofthehostcellwhereitreproducesandtransferittothe
anotherbacterialcellwhichitinfects.Suchphageiscalledtransducingphage.
ItismediatedbylambdaphagethatexperiencesLysogenictypeoflifecycle,
Thevirusinjectsitsnucleicacidintothehostcellandtheviralgenomes
undergoneintegrationwiththebacterialgenomeandremainprophagefora
periodoftimeduringwhichitmultipliesalongwiththereproductionofthe
bacteria,
Delysogenisationoccursandviralgenomedetachesfromthebacterialgenome
toenterthelyticphase,
Viralgenomesbringssomebacterialgenomemayormaynotexchange.

28. Theviralgenomewithsomebacterialgenesnowincludedinnewprogeny
viruseswhicharereleasedafterlysisofthebacterialcell,
Thesebacteriophageswithbacterialgenesinfectnewbacterialcellsinthe
samemannerandtheirgenomegetsintegratedwiththenewhostgenome
andthegeneticrecombinationoccurs,
Thesecondbacterialcellsexpresssomecharactersofthepreviousbacterial
cellbythecourtesyofthevirus,bacteriophage(lambda).
Onthebasisofthegenetransferasmediatedbacteriophage,transduction
mainlyoftwotypes-
GeneralizedTransduction-HeretheLyticcycleisfollowedduring
transduction.
Here,thebacterialDNAisdisintegratedandtheLyticcycleisfollowedas
principle.
ThevirusinsteadofitownsynthesizedDNA,itcollectsbacterialDNAand
introducedtotheanotherbacterialcellbyLyticprocessandintegrateswith
thenewbacterialcell.

29. SpecializedTransduction:Thiskindofgeneticrecombinationisdoneby
theactiveparticipationoflysogenycycle.
Here,thephageDNAisintegratedwiththebacterialDNA-called
prophage.
Itattachedwiththebacterialuntilitbecomesstable,
Afterunstablecondition,itbecomesgetseparatedfromthebacterialDNA,
getseparatedfromthehostbacterialDNAalongwithitssomeofthe
fragmentsofbacterialDNA,
Let,theviralgenomecollects‘gal’genefromthebacteriaandinsertedinto
theanotherbacterialcell,insertthe‘gal’geneintothesecondbacteria,
Now,the2
nd
bacteriacontainstwo‘gal’geneandgetinsertedintothe
bacterialDNA.Nowthenewbacteriacontainstwo‘gal’genesalongwith
thepreexisting‘bio’gene.
Asaresult,thebacteriahasbeengeneticallymodifiedbythevirusvia
transduction.

31. WhenthelysatecontainslowerportionofƛdgitiscalledbyLFT(Lower
FrequencyofTransducing).Whenhighproportionorallprogeny
bacteriophagesareƛdg,thelysateiscalledHFT(HighFrequencyof
Transducing).
MobileDNAelementsreferstodiscretesegmentsofDNAthatmovingas
unitsfromonelocationtootherwithinotherDNAmolecules.Mostmobile
DNAelementsthatconsistsoftransposableelementsandtheprocessby
thisDNAmovementtakesplaceiscalledtransposition.Twotypesof
transposableelementsinBacteriaareInsertionsequences(IS)and
Transposons.Theycarrygenesencodingtransposase,theenzymenecessary
fortransposition.Thesearetwomethodsoftherecombinationinbacteria
arealsofundbesidethetraditionalgeneticrecombinationfoundtooccurin
thisdomain.

32. ACKNOWLEDGEMENT
Googlefordifferentimages,
Differentwebsitesforcontent,
IntroductiontoMicrobiology-Pelzer,ChanandKrieg,
BrookBiologyofMicroorganisms,
Microbiology&Phycology-Dash&Mishra,
AtextbookofMicrobiology-Dubey&Maheswari.
Disclaimer:
Thecontentwriterconveysthanksandacknowledgeshelpfromthefollowingto
developthisarticle.Thishasbeendesignedforonlineresourceswithoutany
financialinterest.