Structure Nutrition and Reproduction in Bacteria By Dr. Neeraj Kumar Tiwari pdf

It is very helpful for integrated course

1. STRUCTURE, NUTRITION
AND REPRODUCTION INBACTERIA
Dr.Neeraj Kumar Tiwari
DepartmentofEducation
Mahatma Gandhi TT College, Mahwa, Dausa Rajasthan

2. MORPHOLOGY OFBACTERIA
❑SIZE:
❖Bacteriaareprokaryotic,unicellular
microorganisms,whichlackingchlorophyll.
❖Thecellstructureissimplerthanthatofother
organismsasthereisnonucleusormembrane
boundorganelles.
❖Duetothepresenceofarigidcellwall,bacteria
maintainadefiniteshape,thoughtheyvaryas
shape,sizeandstructure.
❖Ingeneral,bacteriaarebetween0.2and2.0µm-
theaveragesizeofmostbacteria.
❖E.coli,abacillusofaboutaveragesizeis1.1to1.5
µmwideby2.0to6.0µmlong.
❖Spirochaetesoccasionallyreach500µmin
lengthandthecyanobacterium.
❖Oscillatoriaisabout7µmindiameter.
❖Thebacterium,Epulosisciumfishelsoni,canbe
seenwiththenakedeye(600µmlongby80µm
indiameter).

3. ❖One group ofbacteria,calledthe Mycoplasmas,haveindividuals with size much smaller
thanthesedimensions.
❖Theymeasureabout0.25µandarethesmallestcellsknownsofar.Theywereformerly
knownaspleuropneumonia-likeorganisms(PPLO).
❖Mycoplasmagallicepticum,withasizeofapproximately200to300nmarethoughttobe
theworldsmallestbacteria.
❖Thiomargaritanamibiensisisworld’slargestbacteria,agram-negative.
❖ProteobacteriumfoundintheoceansedimentsoffthecoastofNamibia.
❖Usuallyitis0.1—0.3mm(100—300µm)across,butbiggercellshavebeenobservedupto
0.75mm(750µm).
❖Researchstudieshaveshowntheirsizetoplayanimportantroleinsurvivalovertime.
❖Duetotheirsmallsize,bacteriaareabletoexploitandthrivein
variousmicroenvironments.
❖Thesmallsizeofbacteriaisalso beneficialforparasitismandoligotrophy.
❖Bacteriacancontinuerelyingonarangeofhosts(largeandsmall)fortheirnutrition.In
addition,theycanalsoliveandsurviveinenvironmentsthatcontainalowconcentrationof
nutrients.
❖Bacteriahaveahighsurfaceareatovolumeratiothatallowsthemtotakeupasmany
nutrientsaspossibleforsurvival.Intheprocess,theyareabletocontinuegrowingand
reproducingatasteadyrate.

4. ❑SHAPESANDARRANGMENT:
❖Duetothepresenceofarigidcellwall,bacteriamaintainadefiniteshape,thoughtheyvaryas
shapesize,structureandarrangment.
✓Shapes:
❖Whenviewedunderlightmicroscope,mostbacteriaappearinvariationsofthreemajorshapes:
•Cocci(orcoccusforasinglecell)areroundcells,sometimesslightlyflattenedwhentheyare
adjacenttooneanother.
•Bacilli(orbacillusforasinglecell)arerod-shapedbacteria.
•Spirilla(orspirillumforasinglecell)arecurvedbacteriawhichcanrangefromagentlycurved
shapetoacorkscrew-likespiral.Manyspirillaarerigidandcapableofmovement.Aspecialgroup
ofspirillaknownasspirochetesarelong,slender,andflexible.
Cocci

5. ✓Arrangements:
❖Sofarasthearrangementisconcerned,itmayPaired(diplo),Grape-likeclusters(staphylo)or
Chains (strepto).
➢ArrangementofCocci
❖Coccibacteriacanexistsingly,inpairs(asdiplococci),ingroupsoffour(astetrads),inchains
(asstreptococci),inclusters(asstapylococci),orincubesconsistingofeightcells(assarcinae).
Coccimaybeoval,elongated,orflattenedononeside.Coccimayremainattachedaftercell
division.Thesegroupcharacteristicsareoftenusedtohelpidentifycertaincocci.
1.Diplococci:Thecocciarearrangedinpairs.Examples:Streptococcuspneumoniae,Moraxella
catarrhalis,Neisseriagonorrhoeae,etc.
2.Streptococci:Thecocciarearrangedinchains,asthecellsdivideinoneplane.
Examples:Streptococcuspyogenes,Streptococcusagalactiae

6. 3.Tetrads:Thecocciarearrangedin
packetsoffourcells,asthecellsdividein
twoplains.Followingdivision,thecells
remainattachedandgrowinthis
attachment.Examples:Aerococcus,
PediococcusandTetragenococcus.
4.Sarcinae:Thecocciarearrangedina
cuboidalmanner,asthecellsareformed
byregularcelldivisionsinthreeplanes.
Coccithatdivideinthreeplanesand
remainingroupscubelikegroupsof
eight.Someofthecharacteristics
associatedwiththesebacteriainclude
beingstrictanaerobes,Gram-positive
bacteriaandthatmeasurebetween1.5
and3.oum.Examples: Sarcina
ventriculi,Sarcinaureae,etc.
5.Staphylococci:Thecocciarearranged
ingrape-likeclustersformedbyirregular
celldivisionsinthreeplain.Asmembers
ofthefamilyStreptococcaceae,this
groupofbacteriaischaracterizedby
being non-motile,Gram-positive
Staphylococcusorganisms.Examples:
aureus

7. ➢ArrangementofBacilli
❖Thecylindricalorrod-shapedbacteriaarecalled
‘bacillus’(plural:bacilli).Thesegroupcharacteristics
areoftenusedtohelpidentifycertainbacilli.
1.Diplobacilli:LikeDiplococci bacteria,
Diplobacillioccurinpairs.Followingcelldivision,
thetwocellsdonotseparateandcontinueexistingas
apair.ExampleofSingleRod:Bacilluscereus
ExamplesofDiplobacilli:Coxiellaburnetii,
Moraxellabovis,Klebsiellarhinoscleromatis,etc.
2.Streptobacilli:Thebacilliarearrangedinchains,as
thecellsdivide in one plane.
Examples:Streptobacillusmoniliformis
3.Coccobacilli:Thesearesoshortandstumpythat
theyappearovoid.Theylooklikecoccusand
bacillus. Examples: Haemophilus
influenzae,Gardnerellavaginalis,andChlamydia
trachomatis.
4.Palisades:Thebacillibendatthepointsofdivision
followingthecelldivisions,resultinginapalisade
arrangementresemblingapicketfenceandangular
patternsthatlooklikeChineseletters.
Example:Corynebacteriumdiphtheriae

8. ➢ArrangementofSpiralBacteria
❖Spirilla:(orspirillumforasinglecell)arecurved
bacteriawhichcanrangefromagentlycurvedshape
toacorkscrew-likespiral.Manyspirillaarerigidand
capableofmovement.Aspecialgroupofspirilla
knownasspirochetesarelong,slender,andflexible.
1.Vibrio:Theyarecomma-shapedbacteriawithless
thanonecompleteturnortwistinthecell.
Example:Vibriocholerae
2.Spirilla:Theyhaverigidspiralstructure.Spirillum
withmanyturnscansuperficiallyresemble
spirochetes.Theydonothaveoutersheathand
endoflagella,buthavetypicalbacterialflagella.
Example:Campylobacterjejuni,Helicobacter
pylori,Spirillumwinogradskyi,etc.
3.Spirochetes:Theyhaveahelicalshapeandflexible
bodies.Spirochetesmovebymeansofaxial
filaments,whichlooklikeflagellacontained
beneathaflexibleexternalsheathbutlacktypical
bacterialflagella.Themovementinvolvestheuseof
axialfilaments,whichisoneofthedistinguishing
featuresbetweenthebacteriaandothertypesof
bacteria.Examples:Leptospiraspecies,Treponema
pallidum,Borreliarecurrentis,etc.

9. SHAPESANDARRANGMENT OFBACTERIA

10. ➢OthersShapesandArrangementsofBacteria
❖FilamentousBacteria:Theyareverylongthinfilament-shapedbacteria.Someofthemform
branchingfilamentsresultinginanetworkoffilamentscalled‘mycelium’.
Example:CandidatusSavagella.
❖StarShapedBacteria:Looklikestars(star-shaped).Example:Stellahumosa
❖RectangularBacteria:Theyarerectangularinshaped.Example:Haloarculaspp
❖PleomorphicBacteria:Thesebacteriadonothaveanycharacteristicshapeunlikeallothers
describedabove.Theycanchangetheirshape.Inpurecultures,theycanbeobservedtohave
differentshapes.Examples:Mycoplasmapneumoniae,M.genitalium,etc.
Filamentous
Pleomorphic

11. ULTRASTRUTUREOFBACTERIA
❖Likeotherlivingplantcell,bacterialcellcomprisesacellwall andprotoplast.
❑Slimelayer/Capsule:
❖Slimelayerisagelatinouslayerpresentontheoutersurfaceofcellwall,composedof
polysaccharidesandpolypeptidechainofaminoacids.
❖Whenitsconstituentsareonlypolysaccharideswhichformaviscouslayer,itiscalledslimelayer,
butwhennitrogenoussubstances(i.e.,aminoacids)arealsopresentalongwithpolysaccharides,
thenitiscalledcapsule.
❖Thecapsulatedcellsaredroughtresistant.Associationofpolysaccharideswithothersmakesit
antigeneticallyimportant(usedinserology).
❖Mucopolysacchariedshelpbacteriatoremaininbodywithoutdamage.Mucopolysaccharides
havevirulence(bacteriageneticallycapableofproducingcapsuleifarepathogenic).
❖Ifcapsuleisremovedthecellswilldie.Itmeansthatforsurvivalcapsuleismust.
❖MucopolysaccharidesaresometimesassociatedwithCa
2+,Mg
2+ionsforholdinghigheramount
ofwater.ThecapsuleisremovedbychelatingpolysaccharideslikeEDTAorEDTA+NaClinwhich
cellsaftershaking,shedoffcapsule.
❖InStreptococci,Staphylococcimucilagecapsuleispresentonlywhencellsaredividingrapidly.
❖Slime/Capsuleprotectscellsfromlysozymeactivity.

12. ❑Cellwall:
❖Intheelectronmicrographthecellwallisseenasthin,sharplydefinedenvelopedaroundthe
protoplast.
❖Itrangeinthicknessaround0.02µ.Thecellwallistoughthoughflexible.
❖Theinertandsomwhatrigidcellwalllimitsthevolumeoccupiedbytheprotoplastandthusgives
rigidityandshapetothebacterialcell.
❖Itshowgranularandlacksmicrofibrils.
(a)Structureofcellwall:Thebacterialcellwalliscomposedby4layers.Ofthesetwoareof
higherelectrondensity
❖Theouterlayer(L4)iswavy.Withinitisthelighterlayeroflowelectrondensity(L3).Next
comestheinnerdenseordarkerlayer(L2),isconsideredtobemucopeptidefollowedbythe
innermostlayeroflowelectrondensity(L1).
(b)Chemicalcompositionofcellwall:Thethreemainconstituentsofcellwallare:(i)N-acetyl
glucosamine(NAG),(ii)N-acetylmuramicacid(NAM),and(iii)apeptidechainoffourorfive
aminoacids.Thesetogetherformapolymercalledpeptidoglycanormucopeptide.
❖TheNAGandNAMmoleculeswhicharearrangedalternatively,runinonedirectionandthe
peptidechainruncrosswise.Therigidityofbacterialcellwallisduetothepresenceofthis
polymer.Besidesabovementionedthreeconstituents,someotherchemicalssuchasteichoic
acid,proteinpolysaccharides,lipoproteins.Lipopolysaccharidesarealsodepositedonit.

13. ULTRASTRUTUREOFBACTERIA
CellwallofGrampositivebacteria CellwallofGramnegativebacteria
Grampositivebacteria Gramnegativebacteria

14. ❑Protoplast:
❖Aliving,slightlyviscousstuffcalledprotoplastisdifferentiatedinto:
(a)Cytoplasmicmembrane:Innertocellwall,asemipermeablecytoplasmicmembraneis
presentwhichisabout75A
0thick.Chemicallyitiscomposedofadoublelayerofphospholipid
molecules.Proteinsarefoundembeddedinthelipidbilayers.Thecytoplasmicmembranehas
manyfoldedstructurescalledmesosomeswhichareassociatedwithnumberofactivitieslike
seatforproteinsynthesis,respiratoryfunction,multiplicationofchromosomalDNA,andDNA.
Plasmamembranecontainsspecialreceptormoleculesthathelpbacteriadetectandrespondto
chemicalsintheirsurroundings.Italsocontrolstheentryoforganicandinorganicmolecules.
(b)Cytoplasm:Bacterialcytoplasmisacomplexmixtureofcarbohydrates,proteins,lipids,
minerals,nucleicacidsandwater.Itstoresorganicmaterialintheformofglycogen,rolutinand
poly-β-hydroxybutyrate.Besidesfluidportionandstorageparticles,thebacterialcytoplasm
alsocontainchromaticornuclearareaandsomeotherinclusions.Thebacterialcellisdevoid
cellorganellesbutthephotosyntheticbacteriahavechromatophoresintheircytoplasm.
Ribosomesarethesitesofproteinsynthesisandsuspendedfreelyincytoplasm.Theirnumber
variesfrom10,000to15,000inacell.Bacterialribosmoesare70stype(50sand30ssubunits)
consistsoftwosubunits.Mesosomesarecomplexlocalizedinfoldingsofthecytoplasmic
membraneandhigherinbacteriawhichshowhighrespiratoryactivity,suchasnitrifying
bacteria.Ithasbeensuggestedthatmesosomesservestoaccommodatemorecentresof
respiration.ButtheabsenceofenzymeslikeATPase,dehydrogenaseandcytochromein
mesosomeindicatesthattheyarenotthesitesofrespiration.Theyprobablyparticipateinthe
formationoftransverseseptumduringcelldivision.

15. (c)Thenuclearapparatus:
❖Thebacterialnucleusdevoidofnuclearmembrane,nucleolus,chromonemataandnuclearsap,
suchstructureiscallednucleoidorgenophore.
❖TheDNAmolecule(maybedoubleorsingle)isapproximately1,000µmlong,usuallyforming
ringlikestructureorsometimesremaindiffusedthroughoutthecytoplasmofthecell.The
BacterialDNAisdevoidofhistonesandreferredasbacterialchromosome.
❖Bacterialcellsalsocontainsomeextrachromosomalhereditydeterminantswhichareeither
independentofbacterialchromosomesorareintergratedwiththemcalledplasmid.
❖Extranuclearmaterialscalledasepisomearepresentwhichmaybelinear,circular,covalent
coiledcircular.Lederberg(1952)gavethetermplasmidtothoseextragenophoralgenetic
materials.Thereplicationofplasmidseemsselfcontrolled.Theycontaindifferentnon-
essentialcharacters.
❖Basedonhostproperties,theplasmidsareclassifiedintodifferenttypesas:
•F-factorforfertility
•Col-factorforcolicinogeny
•R-factorforresistance
•Tumorinducingplasmid(Agrobacterium)
•Degradativeplasmid(Pseudomonas)
•Pathogenicitytomammals
•Penicillaseplasmid(Staphylococcus)
•Mercuryresistance
•Crypticplasmids
❖Twoimportantgenesareassociatedwithplasmidsori(originofreplicon)andtra(transfer).

16. LOCOMOTION INBACTERIA
❖Somebacteriaareselfmotile.Theyareswimthroughtheliquidinwhichtheylive.Theycan’t
crawloverdrysurfaceorflythroughtheair.Motilityisuniversalamongthespirilla,common
amongthebacillibutlackingorrareincocciforms.
❖Theorganofthelocomotionissmallwhipsorhairlikeappendagescalledflagella.
❑Flagellation
❖Theflagellaaredistributedoverthesurfaceofthebacterialcellinacharacteristicmanner.Their
number,positionandarrangementvarieswiththespecies.Onthebasisoftheflagellationand
arrangementthebacterialcellcanbeclassifiedas;
(a)Polarflagellation:Thistypeofflagellationisrestrictedtoaratherhomogenousgroupof
bacilliandspirilla.Theyareallgramnegative.Thesearethefollowingtype;
•Monotrichous:Oneflagellaatoneend,e.g.Vibriochlolerae,Pseudomonas
•Amphitrichous:Oneflagellaateachend,e.g.Nitosomonas,Spirillum
•Cephalotrichous:Twoormoreflagellaatoneendonly,e.g.Pseudomonasfluorescens
•Lophotrichous:Tuftsofflagellaatboththeends,e.g.Spirillumvolutans
(b)Non-polarflagellation:Inthiscaseflagelladistributeduniformlyalloverthebodysurface.
•Peritrichous:Flagelladistributedevenlyalloverthebody,e.g.,Proteusvulgaris
•Atrichous:Bacteiawhichlackflagella,e.g.,Lactobacillus

17. ARRANGMENT ANDSTRUCTUREOFFLAGELLA
AtrichousMonotrichous Amphitrichous
Cephalotrichous
Paritrichous
Lophotrichous

18. ❑StructureofFlagellum
❖Flagellainbacteriahasspecialsignificance(a)ahookisalwayspresentandisneverstraight(b)
eukaryoticflagellahas9+2arrangementsofmicrotubuleswithassociationtoeachotherhave
proteinattachmentscalledspokes.
❖Lateralsofperipheraltubulesaremadeofproteindinein;butinprokaryoteslikebacteriaf
lagellaorganizationissimple.Flagellumismadeupofcontractileproteincalledflagellin.There
arepolymersofthisattachedlaterally/longitudinallybyspecialbondagewiththeresultthat
theremaybe5-6subunitsarrangedinspiralscreatinghollowincentre.
❖Basalbodystructureinbotheukaryotesandprokaryotesaredifferent.Inprokaryotesthebasal
subunitshasonly4discs.Throughhookflagellumpassesandwholestructureisjoinedbyaf
lagellinrod.
❖Asortofleversystemisprovidedbytheserings.AfixedpositionofrodL,P,Shaveahollow
centrethroughwhichrodpassesandactasbearingsofmovementofflagella.Periplasmicspace
providestheforceforrotationbyionicstrengthandthesourceofmotionisnotATP.
❖Ingramnegativebacteriumpeptidoglycanlayerisverysmallandonly2ringsareavailableand
hookisnotasrigid.Ifbacteriumispresentinwater,theresistancetothecellisverylarge.Thus
formovementveryhighforceisrequired,usuallythemovementisanticlockwise.Withthis
movementthecellispushedforward.Thisrotationisnotconstant.Aftersometimethecell
eitherstopsorflagellachangesitsdirectiontoclockwisemovement.
❖Thusthemovementofbacteriaiszig-zagorBrownianmovement.Rotationofflagellais
unique.Motioniscontrolledbyionicbalanceinperiplasmicspace.

19. NUTRITIONINBACTERIA

20. NUTRITIONINBACTERIA
❖Mostofthebacteriadonotcontainchlorophyll.Theyareunabletosynthesizetheirownfood,
butasmallgroupofbacteriaarecapableofsynthesizingtheirownfood.
❖So,nutritioninbacteriaisbothautotrophicandheterotrophic.
❑Autotrophicbacteria:
❖Thebacteriawhichsynthesistheirownfood(organiccompound)necessaryforstructureand
metabolismfromthesimpleinorganiccompound,iscalledautotrophic.Theyarefurther
dividedinto2types,photosyntheticandchemosyntheticaccordingtotheenergyutilization.
Thustheformercalledphotosyntheticautotrophsandthelaternon-photosynthetic
autotrophs.
✓PhotosyntheticBacteria:Theycanpreparetheirfoodbyusingsolarenergyinthepresenceof
photosyntheticpigmentbacteriochlorophyllandchlorobiumchlorophyll.Photosynthesisin
bacteriadiffersfromothergreenplantsbecausethereisnoreleaseofoxygeninphotosynthesis.
Suchphotosynthesisiscalledanoxygenicphotosynthesis.Itisoffollowingtypes:
Greensulphurbacteria:
Purplesulphurbacteria:
Non-sulphurbacteria :
Thephotosyntheticpigmentischlorobiumchlorophyllandsulphur
isby-product.e.g:Chlorobium
Thephotosyntheticpigmentisbacteriochlorophyllandsulphuris
by-product.e.g:Chromatium
Thephotosyntheticpigmentbacteriochlorophyllandsulphurisnot
aby-product.e.g:Rhodopseudomonas

21. ✓ChemosyntheticBacteria:Thesebacteriapreparetheirfoodbyusingchemicalenergyinthe
absenceofphotosyntheticpigment.Theygetenergyforfoodsynthesisbytheoxidationof
certaininorganicsubstancessuchasammonia,nitrites,nitrate,ferrousiron,hydrogensulphides
andanumberofmetalicornonmatelicmaterialsavialableintheenvironment.Thebacteria
absorbinorganicmoleculesofthesubstanceintothebodywherethechemicalreactiontakes
place.Inthisreactionthechemicalbondsarebrokenandenergyisresleased.Thisenergyisused
bythebacteriaandthisprocessiscalledchemosynthesis.Itisfollowingtypes:
•Sulphurbacteria:Theyusechemicalenergywhilethereisoxidationofsulphurcompound.E.g:
Thiobacillus
2H2SorS2+O2=======➔2S +2H2O+ energy
•Ironbacteria:Theyusechemicalenergywhilethereisoxidationcompound(Fe
2+toFe
3+).E.g:
Leptothrix,Ferobacillus,Cladothrix
4FeCO3+O2+6H2O=======➔4Fe(OH)3+4CO2+Energy
•Hydrogenbacteria:Theyusechemicalenergywhilethereisoxidationofmolecularhydrogen.
E.g:Pseudomonas,Hydrogenomonas,Bacilluspectotrophus.
H2+½O2=====➔H2O+ Energy
•Nitrifyingbacteria:Theyusechemicalenergywhilethereisoxidationofnitrogencompound.
E.g:Nitrosomonas,Nitrobacter
2NO2+O2=========➔2NO3+Energy

22. Differencebetweenchemosynthesisand photosynthesis
Parameters Chemosynthesis Photosynthesis
AmountofenergyTheamountofenergyavailablein
thechemosynthesisismuchlessas
comparewithphotosynthesis
Theamountofenergyavailableinthe
photosynthesisismuch moreas
comparewithchemosynthesis
Gainofenergy Thereisnogainofenergyfrom
outsidetheplanet
Thereisdistinctgainofenergyfromthe
outsidetheplanet.
Energyinput Nolightisinvolveintheprocess Ittakeplaceinthepresentofsunlight
Typeofenergy Reactionareallexothermic Thereactionsareendothermic
Energyrequiredfortheprocessis
obtainedbytheoxidationof
certaininorganicsubstances
availableintheenvironment
Solarenergytrappedbythepigmentis
usedintheprocess
Pigments Nopigmentsarerequired Bacteriochlorophyll, chlorobium
chlorophyll
Bacteria Purplesulphurbacteriaandgreen
sulphur bacteria. E.g.,
Pseudomonas,Thiobacillus
Sulphurbacteria,ironbacteria,
nitrifyingbacteria,hydrogenbacteria.
E.g.,Rhodospirillum,Chlorobium
Example H2S+CO2======➔(CH2O)+S+
H2O (inthe presence ofsun light,
pigment)
4FeCO3+O2+6H2O=======➔Fe(OH)3+
4CO2+Energy

23. ❑Heterotrophicbacteria:
❖Theheterotrophicbacteriawhichformthemajoritycannotsynthesizedorganiccompounds
fromthesimpleinorganicsubstances.Lackingthepigmenttheycannotcapturethesolar
energywhichisessentialforthesynthesisthesubstancestheyneedasfood.Thusthesetypeof
bacterialivewheretheorganicfoodisreadilyavailableeitherfromlivingorganism.
✓Saprophyticbacteria:Theygrowindead,decayingorganicmaterialandlivebydigestingand
absorbingthem.Thesebacteriagraduallybreakdowncomplexorganiccompoundsintosimpler
products.Fordoingsotheysecretingtheenzymes.Thebreakdownofcarbohydrateiscalled
fermentation(e.g.,Lacticacidbacteria).Thebreakdownofproteinmaterialcalledputrefaction
(nitrifyingbacteria).
✓Parasiticbacteria:Parasiticbacterialiveonandwithinotherorganisms(host)andtheyobtain
theirnutritionfromthehost.Theyliveonorwithintheorganismsbothplantsandanimals.If
theparasiticbacteriacausediseasesandareharmfulfortheirhosttheyarecalledpathogenic.If
theparasiticbacteriacannotcausediseasesandareharmlessfortheirhosttheyarecallednon-
pathogenic.e.g.:Vibriocholerae,Diplococcuspneumoniae.Manydiseasesincludingplantand
animalincludingthemanarecausedbythepathogenicbacteria.
✓Symbioticbacteria:Symbioticbacterialiveincloseassociationwithotherlivingorganismsso
thattheybotharebenefitedtoeachother,neitherofthemisharmed.e.g.:Rhizobium.Certain
plantsestablishasymbioticrelationshipwithbacteria,enablingthemtoproducenodulesthat
facilitatetheconversionofatmosphericnitrogentoammonia.Itappearsthatnotonlymustthe
planthaveaneedfornitrogenfixingbacteria,buttheymustalsobeabletosynthesize
cytokininswhichpromotetheproductionofrootnodules,requiredfornitrogenfixation.

24. REPRODUCTION INBACTERIA
Reproduction
Asexual
Reproduction
Vegetative
Reproduction
Sporulation
Sexual
Reproduction
Conjugation Transduction Transformation
Fission
Budding
Cyst
Segmentation
Conidia
Oidiospore
Sporangiospore
Endospore
Sterilemale
method
Fertilemale
method
Generalized
Transduction
Specialized
Transduction

25. REPRODUCTION INBACTERIA
❖Asexualreproductionischaracteristicofallbacteria.Sexualreproductionwaslongthroughto
beabsentbutinvestigationwiththehelpofelectronmicroscopehaveclearlydemonstratedthe
exchangeofgeneticmaterialinsomespeciesofbacteria.
❑Asexualreproduction:It takeplacebytwomethods:(i)Vegetative,(ii)Sporulation
➢Vegetativereproduction:Ittakeplacebythefollowingmethods.
✓BinaryFission:ThemostcommonwaybywhichthebacteriareproduceitselfistheBinary
Process.Itisaprocessbywhichasinglebacterialcellsimplydividesintotwoinhalfanhour
time.Thevariouseventsofbinaryfissionareasfollows:
•Thenucleoidgraduallybecomeelongatedinsizeandformdumbel-shapedstructure.
•Theystillremainattachedtotheplasmamembranewiththehelpofmesosome.
•TheduplicationofDNAandmesosometakesplaceandgetseparatefromeachother.
•Thedaughtermesosomesandnucleoidsmigratetowardstheoppositepoles.
•Theplasmamembraneinvaginatesatthecenterandtheparentcellisdividedintotwo
identicalcells.
✓Budding:Inthiscase,asmallprotuberance,calledbud,developsatoneendofthecell.
Genomereplicationfollows,andonecopyofthegenomegetsintothebud.Thenthebud
enlarges,eventuallybecomeadaughtercellandfinallygetsseparatedfromtheparentcell.Itis
comparativelyrareprocessobservedinfewbacterialikeRhodopseudomonas,Hyphomicrobium,
Pedomicrobium,Hyphomonasetc.Hyphomicrobeales,commonlycalledthebuddingbacteria,a
branchstrandofcellwallmaterialmaybeinitiatedpriortotheseparationofabud.

26. ✓Cysts:Incertainbacteriatheentireprotoplastofthecellrecedesfromthecellwallandbecomes
rounded.Athickwallisthensecretedaroundittoformresistantstructuresomewhatsimilarto
theendospore.Itiscalledthecyst.TheseareformedincertainspeciesofAzobacter.Under
suitableenvironmentconditionsthecystgerminatetoproducethenewbacterium.
✓Segmentation:Insomeotherspeciesofbacteriareproducevegetativecalledsegmentation.In
thiscasetheprotoplastofthebacteriumcellatsomestage,dividestoformverytinybodycalled
gonidia.Thecellwallrupturedandthelibratedtinygonidiagrowintonewbacteriumcellunder
suitableconditions
Budding
BuddinginHyphomicrobiales Segmentation
Cyst
Fission

27. ➢Sporulation:Somebacteriaproducenonmotile
sporeswhichareofthefollowingtypes:
✓Conidia:Manyfilamentousbacteria(e.g.,
Streptomyces)formchainsofsmall,sphericalspore-
likeconidiaatthetipsofthefilaments.Aconidium
developsbytheformationofatransversewallatthe
tipofthefilament.Thefilamentbearingconidiaare
knownasconidiophores.Afterliberationeach
conidiumgivesrisetoanewfilamentousbacterium,
providedconditionsforgerminationarefavourable.
✓Oidiospores: In an another member Actinomyces he
hyphainseadofobstructingsporeinsuccessionat
thefreeend,undergodesadditionalseparation
throughitslnghttoformnumeroussmall
reproductiveunitsknownasoidiospores.Each
oidiosporesongerminationproduces,afilamentous
bacterium.
✓Sporangiospores:Insomebranchingbacteria
sporangialikestructuremaydevelopedattheendof
certainhyphae.Theprotoplastofthesporangiamay
dividedtoformtinysporangiospores.Onlibrationof
thesesporesgerminateundersuitablecondition,each
producingafilamentousbacterium.
Conidia
Conidiophore
Oidiospores
Sporangium
Sporangiospores

28. ✓Endospore
❖Duringtheunfavorablecondition,eubacteria
havetheabilitytobecomeendospores.
❖Inthisstate,thebacteriacantolerate
exceedinglyhighandlowtemperatures,acidic
andbasicconditions,andlargeamountsof
radiation.
❖Endosporesareextremelyhardtokill.
Surprisingly,theycanbeboiledforhoursand
stillsurvive.
❖EndosporescanonlybemadebyGram-
positivebacteria.
❖Withintheendosporeremainsthebacterial
DNA,butthecytoplasmhasadecreasedwater
concentration.
❖Thisisthoughttohelpinprotectingagainst
highheat.Thebacteriawilltakeonatough
coatingcomposedofcalciumanddipicolinic
acid,creatingadenseandimpregnablebarrier
tostabilizetheDNAwithinthecell.DNA
repairenzymesarealsostillactive,aidingin
theresistanceoftheendospore.

29. ✓Endosporeformation:
❖Thesearespecializedstructuresproducedforthecellstidingoverunfavourableconditionstothe
extentthattheyareheatresistantevenat80
oCfor10minutes(duringpasteurization).Theycan
withstanddraughtandcansurviveforyears(200years).Theycansurviveinradiationalsoand
canwithstandacidtreatments(conc.H2SO4).
❖Theirpresenceisverywidelydistributedamongvariousgroupsofbacteriaandalmostallthose
bacteriawhichshowendosporesaregrampositiveexceptoneArchebacterium.
❖Thesesporesareformedinbothaerobicandanaerobicforms.Sporeformationisobservedunder
conditionsofrestrictedgrowthstartingwithaccumulationofproteinrichcontentinspore
formingregion.Numerousmetabolicconversionsoccursduringsporeformationsometimesat
theexpenseofPHBAandaswellaspolysaccharideduringanaerobic.Duringfirsthourproteinof
specificnatureisformedthereservefoodgetsdepleted.Dipicolenicacidissynthesizedwhichis
notusuallyassociatedandaccumulated.These2diaminopimalicacidandCa
2+actsaschelate
andmakesupto10-15%ofdryweight.
❖Equaldivisionstartsfromperipheryoftheplasmamembrane.Twocellsarespecificallyformed,
onesmallandotherlarge.Assoonasitoccurs,thelargecellstartsengulfingthesmalleroneso
thatthesporebecomesembeddedintheoriginalcell.Itisatthisstagethatsporecoatislaid
down.SporecoatbecomesdoublewalledstructureswithDPAaccumulatedincortexregion.
Outersporeenvelopeisformedbymothercellandisformedofpolysaccharidewhichmay
remainassuchoradditionallyaexosporiummaybelaidinB.ceriuswhichisalsoformedof
mothercell.Thisexosporiumremainsasloose,discretestructureinmaturespore.Asmatureone
isgettinginvestingbycorticalregionmuchofthewaterislost.Thisstateisreachedin7-8hours
whichresultsincompletionofendosporeformation.

30. ❑Sexualreproduction:Thefollowingpointshighlightthemethodsofsexual
Reproduction(ParaSexuality)inBacteria,i.e.,Conjugation,TransformationandTransduction.
➢Conjugation:ItwasfirstdiscoveredinEscherichiacolibyLederbergandTatum(1946).They
foundthattwodifferenttypesofauxotroph(nutritionalmutants)growntogetheronminimal
mediumproducedanoccasionalprototroph(wildtype).
❖Cellcontactwasrequiredforthischange.Anderson(1957)observedconjugationbetweentwo
suchbacteriaunderelectronmicroscope.Conjugationwaslaterreportedinanumberofother
bacteria.Bacteriashowingconjugationaredimorphic,i.e.,theyhavetwotypesofcells,male
(F
+)ordonorandfemale(F-)orrecipient.
❖Themaleordonorcellpossesses1-4sexpilionthesurfaceandfertilityfactor(transferfactor,sex
factor)initsplasmid.Fertilityfactorcontainsgenesforproducingsexpiliandothercharacters
neededforgenetransfer.
❖Sexpiliare1-4narrowprotoplasmicoutgrowths.Bothsexpiliandfertilityfactorareabsentin
femaleorrecipientcells.
❖Ifthesetwotypesofcellshappentocomenearer,apilesofmalecellestablishesaprotoplasmic
bridgeorconjugationtubewiththefemalecell.Ittakes6-8minutes.Geneexchangecanoccur
bytwomethods;
✓SterileMaleMethod(F
+xF
–→F
–becomesF
+):Theplasmidhavingfertilityfactorreplicates.
Acopyofitgetstransferredtotherecipientcellthroughtheconjugationtube.Therecipientcell
alsobecomesdonor.Thephenomenonofreversibilityofsexiscalledsexduction.

31. Conjugationinbacterialcells
Conjugationin bacterial:A:Sexduction(Sterilemalemethod)B:FertileMaleMethod
B
A

32. ✓FertileMaleMethod(HfrxF
–→F
–remainsF
–):TheF
+plasmidorfertilityfactorofthe
donorcellgetsintegratedtobacterialchromosomeorDNA.Theattachableplasmidisknownas
episome.
❖Thepointatwhichplasmidgetsintegratedtobacterialchromosomediffersindifferentstrains.
Integrationispossiblebecausecertainnucleotidesequencespresentinbacterialchromosome
arecompatiblewithsequencesinplasmidDNA.
❖ThedonorcellhavingfertilityfactorintegratedtoitschromosomeiscalledHfr(highfrequency
ofrecombination),metamaleorsupermalebecauseithasarecombinationfrequencyof1000
timesmoreascomparedtonormalF
+.
❖Non-integrated F
+plasmids disintegrate in her cells.TheintegratedF
+
factor breaks the
bacterialchromosomeatoneendofitsattachment.Thebacterialchromosomenowundergoes
replication.
❖Acopyofthefreedendofbacterialchromosome(enddistaltoF
+factor,alsocalledzeroend)
passesintotherecipientcellthroughtheconjugationtube.Fertilityfactoristhelasttodoso.
❖Generallywholeofbacterialchromosomedoesnotpassintorecipientcell.F
+factorisveryrarely
transferredasconjugationismaintainedforabriefperiod.Onlyafewgenesaretransferred,one
insevenminutes,twoinnineminutes,threeintenminutes,fourinelevenminutes,etc..
❖Conjugationproducesanincompletelydiploid“zygote”knownasmerozygoteorpartialzygote.
Thenewgenesmayreplacethegenespresentintherecipientcells(thoseoftherecipientcells
disintegrate)orgetaddedtothem.

33. ➢Transformation:ItistheabsorptionofDNAsegmentfromthesurroundingmediumbya
livingbacterium.ThephenomenonwasdiscoveredbyGriffithin1928.Itsmechanismwas
workedoutbyAvery(1944).
❖Intransformation,abacteriumtakesinDNAfromitsenvironment,oftenDNAthat'sbeenshed
byotherbacteria.IftheDNAisintheformofacircularDNAcalledaplasmid,itcanbecopied
inthereceivingcellandpassedontoitsdescendants.
❖Receptivityfortransformationispresentforabriefperiodwhenthecellshavereachedtheend
periodofactivegrowth.Atthistimetheydevelopspecificreceptorsitesinthewall.NormallyE.
colidoesnotpickupforeignDNAbutitcandosointhepresenceofcalciumchloride.

34. ➢Transduction:Itisthetransferofforeigngenesbymeansofviruses.Transductionwasfirst
discoveredbyZinderandhisteacherLederberg(1952)inSalmonellatyphimurium.
❖Suchavirusisnevervirulent.Itpassesoverthegeneoftheprevioushosttothenewhost.
Transducingvirusesmaycarrythesamegenes(restrictedtransduction)ordifferentgenes
(generalizedtransduction)atdifferenttimes.
❖Thegeneticrecombinationinwhichgeneticmaterialistransferredbyphagevirusbetweentwo
bacteriaiscalledtransduction.Ithastwoforms:
✓Generalizedtransduction:Itoccursinlyticcycleofphagevirus.DNAofphagesvirusenter
intoE.colibacteria.ThisDNAreplicatesanddevelopsmanynewDNAand capsids.
❖TheDNAofbacteriaisbroken.SomepiecesofDNAalsoenterintocapsidofvirus.Bacteria
burstandreleasenewphageviruses.Nowthisphageentersintorecipientbacteriaandtransfer
DNAofdonorbacteriaintotheDNAofrecipientbacteria.
❖Bacterial endonucleasesenzymesdestroythephagevirus.Nowthesebacteriaincorporategenes
ofdonorbacteriaandreplicates.
✓Specializedtransduction:ItoccursinLysogeniccycleofphagevirus.InthiscycleviralDNA
incorporateintobacterialDNAasprophage.
❖Itremainspeacefullythere.Butsometime,itbecomeslytic.ItcomesoutofbacterialDNA.
SomepartofbacterialDNAremainattachwithit.
❖ViralDNAwithapieceofbacterialDNAreplicatesanddevelopsnewcapsids.Bacteriaburst.
Virusinfectsotherbacteriaandtransfergenesofdonor.

35. Transductionin bacterialcells