Bacteria differ from viruses very much. First of all, they are bigger, second of all, they represent quite self-sufficient live organisms capable of self-reproducing if corresponding feeding is available. Penetrating to a human body, certain bacteria find food and suitable conditions for reproduction, and diseases are appeared this way.

1. WHAT IS BACTERIA?
Bacteriadifferfromvirusesverymuch.Firstof all,theyare bigger,secondof all,theyrepresentquite
self-sufficientlive organismscapable of self-reproducingif correspondingfeedingisavailable.
Penetratingtoahuman body, certainbacteriafindfoodandsuitable conditionsforreproduction,and
diseasesare appearedthisway.
Before the XXcentury,the doctors’fightagainstbacterial infectionshasnotdifferedfromfighting
againstinfectionvirus:all theireffortsweredirectedathelptoan organismto cope witha disease.
Fortunately,the possibilitiesof modernmedicineare significantlyincreased.Itwasdue tocreationof
several groupsof medicationsabletokill microbeswithoutanysignificantharmto an individual.You,
for sure,heardaboutthese medications:antibiotics(Penicillin,Tetracycline,Gentamycin),
sulfanilamides(Streptocide,Aethazolum, Biseptol) andetc.
Readingthese words,the readersmaythinkthatbacterial infectionsare treatedmucheasier,comparing
to infectionvirus.Butunfortunately,thisisnotlike this.Firstof all,because bacteriashow incredible
adaptabilityandasthe doctors discovernew medications,new speciesof knownbacteriarefractoryto
these antibioticsare appeared(orprobablythe drugsaffectbacteriafora short periodof time ornot
veryeffectively.)Secondof all,the same bacterial diseases,forexample,pneumoniaormeningitis,may
be causedby hundredsdifferentmicrobesandthe doctors,sometimes,are notable toanswera
question:“Whatisthe reason?”and, accordingly,prescribethe correctantibiotic.
The worldof bacteriaisdiverse,aswell asthe diseasescausedbybacteriaare variousandnumerous.
Bacteriadifferfromeachotherinthe sizes,structure,reproductiveabilities.The conditionssuitable for
theirnormal existingare various.Some bacteriaare round,theyare namedcocci (staphylococcus,
pneumococcus,streptococcus,meningococcus,gonococcus,)othersare oblong,theyare namedrods
(dysentericbacillus,pertussisandcolonbacillus).Bacteriahave outgrowth,flagellum,andcilium.In
contrast to viruses,bacteriaare notcharacterizedbyselective lesionof certainhumanbodyparts.
However,eachmicrobe hasown“preferences.”So,dysentericbacillusisdevelopedinthe large
intestine,pertussisagentisdevelopedinthe epitheliumcellsof the respiratorytracts,meningococcus
agentis developedinthe arachnoidmembrane.Staphylococcusmaycause aninflammatoryprocess
anywhere onthe skin,inbones,inlungs,andinintestines,andetc.
The word bacteriaisthe plural of bacterium.Grammaticallythe headline shouldjustsay“Whatare
bacteria?”The incorrectusage has beenincludedinthe headlinetoremindreadersthatitiswrong –
and hopefullyhelpcorrectanincreasinglycommonmistakeinthe Englishlanguage.
Bacteria are tiny living beings (microorganisms)
theyare neitherplantsnoranimals –theybelongtoa group all bythemselves.Bacteriaare tinysingle-
cell microorganisms,usuallyafewmicrometersinlengththatnormallyexisttogetherinmillions.

2. A gram of soil typicallycontainsabout40 millionbacterial cells.A milliliterof freshwaterusuallyholds
aboutone millionbacterial cells.
PlanetEarthis estimatedtoholdatleast5 nonillionbacteria.Scientistssaythatmuchof Earth’s biomass
ismade upof bacteria.
5 nonillion=5,000,000,000,000,000,000,000,000,000,000 (or 5×1030)
(Nonillion=30 zerosin USA English.InBritishEnglishitequals54zeros.Thistextusesthe American
meaning)
Bacteria come in three main shapes:
1) Spherical (like a ball)
These are usuallythe simplestones.Bacteriashapedlike thisare calledcocci (singularcoccus).
2) Rod shaped
These are knownas bacilli (singularbacillus).
Some of the rod-shapedbacteriaare curved;these are knownasvibrio.
3) Spiral
These knownare as spirilla(singularspirillus).
If theircoil is verytighttheyare knownas spirochetes.
There are manyvariationswithineachshape group.
Bacteriamorphology.Image byVojtěchDostál
Bacteria are found everywhere
Bacteriacan be foundin:
 Soil
 Radioactive waste
 Water
 Plants
 Animals
 Deepinthe earth’scrust
 Organicmaterial
 Arctic ice
 Glaciers
 Hot springs

3.  The stratosphere (between6to30 milesupinthe atmosphere)
 Oceandepths – theyhave beenfounddeepinoceancanyonsandtrenchesover32,800 feet
(10,000 meters) deep.Theylive intotal darknessbythermal ventsatincredible pressure.They
make theirownfoodby oxidizingsulfurthatoozesfromdeepinsidethe earth.
Scientistswhospecialize inbacteria –bacteriologists –say bacteriaare foundabsolutelyeverywhere
exceptforplacesthathumanshave sterilized.Eventhe mostunlikelyplaceswheretemperaturesmay
be extreme,orwhere there maybe a highconcentrationof toxicchemicals,have bacteria.These
bacteriaare knownasextremophiles(anextremophileisanyorganismadaptedtolivinginconditionsof
extreme temperature,pressure,or/andchemical concentrations) andcansurvive where noother
organismcan.
Bacteria cells
A bacterial cell differssomewhatfromthe cell of aplantor animal.Bacterial cellshave nonucleusand
otherorganelles(sub-unitswithinacell withaspecificfunction) boundbyamembrane,exceptfor
ribosomes.Bacteriahave pili,flagellaanda cell capsule (mostof them),unlikeanimal orplantcells.An
organismwithoutanucleusiscalledaprokaryote.
A diagramof a bacterial cell.
A bacterial cell includes:
 Basal body – thisanchors the base of the flagellum, allowingitto rotate.
 Capsule – a layeron the outside of the cell wall.Some bacteriadon’thave acapsule.
 Cell wall –a thinlayer(membrane)outsidethe plasmamembrane,andwithinthe capsule.
 DNA (Deoxyribonucleicacid) – containsall the geneticinstructionsused inthe developmentand
functioningof the bacterium.Itisinside the cytoplasm.
 Cytoplasm– a gelatinoussubstanceinside the plasmamembrane.Geneticmaterialand
ribosomeslie inside.
 Flagellum–thisisusedformovement;topropel the cell.Some bacterial cellshave more than
one.
 Pili (singular:pilus)–these spikesallowthe cell tosticktosurfacesand transfergeneticmaterial
to othercells.A studyrevealedthatpili are involvedincausingtraveler’sdiarrhea.
 Plasmamembrane –it generatesenergyandtransportschemicals.Substancescanpassthrough
the membrane (permeable).Itislocatedwithinthe cell wall.
 Ribosomes –thisiswhere proteinismade (synthesized).Ribosomesare small organellesmade
up of RNA-richgranules.
The origins and evolution of bacteria
Modernbacteria’sancestors – single-celledmicroorganisms –appearedonearthabout 4 billionyears
ago. Scientistssaytheywere the firstlifeformsonEarth.For the following3billionyearsall lifeforms

4. on Earth were microscopicinsize,andincludedtwodominantones:1.Bacteria,and2. Archaea
(classifiedasbacteria,butgeneticallyandmetabolicallydifferentfromall otherknownbacteria).
There are fossilsof bacteria.However,becausetheirformandstructure (morphology) are not
distinctive itisvirtuallyimpossible todate them, makingitextremelyhardtostudythe processof
bacterial evolutionwithanydegree of accuracy.However,withthe helpof gene sequences,itisnow
possible toknowthatbacteriadivergedfromtheiroriginal archaeal/eukaryoticancestry(Eukaryotic=
pertainingtoaneukaryotice;asingle-celledormulticellularorganismwhosecellscontainadistinct
membrane-boundnucleus).
Archaeais bacteria’smostrecentcommonancestor – it wasmost likelyhyperthermophile,anorganism
that thrivedinextremelyhotenvironments,approximately2.5– 3.2 billionyearsago.Bacteriawere also
involvedinthe divergence of archaeaandeukaryotes.Eukaryotescame fromaveryearlybacteriawhich
had an endosymbioticassociation(whenanorganismliveswithinthe bodyorcellsof anotherorganism)
withthe predecessorsof eukaryotescells,whichwereprobablyrelatedtothe Archaea.Biologistssay
that some algae probablyoriginatedfromlaterendosymbioticrelationships.
Put simply
bacteriawere the firstorganismstoappearon earth,about4 billionyearsago.Ouroldestknownfossils
are of bacteria-likeorganisms.
On the next page
we lookat a shorthistoryof bacteriology,how bacteriafeedthemselvesandwhatkindsof
environmentsbacteriainhabit.Onthe final page we discusshow bacteriareproduce andthe effectsof
bacteria
Bacteriaare microscopicsingle-celledorganismsthatthrive indiverseenvironments.Theycanlive
withinsoil,inthe oceanandinside the humangut.Humans’relationshipwithbacteriaiscomplex.
Sometimestheylendahelpinghand,bycurdlingmilkintoyogurt,orhelpingwithourdigestion.Atother
timestheyare destructive,causingdiseaseslikepneumoniaandMRSA.
Structure
Basedon the relative complexityof theircells,all livingorganismsare broadlyclassifiedaseither
prokaryotesoreukaryotes.
Bacteriaare prokaryotes.The entire organismconsistsof asingle cell withasimple internal structure.
Unlike eukaryoticDNA,whichisneatlypackedintoacellularcompartmentcalledthe nucleus,bacterial
DNA floatsfree,ina twistedthread-like masscalledthe nucleoid.
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5. Bacterial cellsalsocontainseparate,circularpiecesof DNA calledplasmids.Bacterialackmembrane-
boundorganelles,specializedcellularstructuresthatare designedtoexecutearange of cellular
functionsfromenergyproductiontothe transportof proteins.However,bothbacterial andeukaryotic
cellscontainribosomes.These spherical unitsare where proteinsare assembledfromindividual amino
acids,usingthe informationencodedinastrandof messengerRNA.
On the outside,bacterial cellsare generallysurroundedbytwoprotectivecoverings:anoutercell wall
and an innercell membrane.However,certainbacteria,like the mycoplasmasdonothave a cell wall at
all.Some bacteriamayevenhave a third,outermost,protective layercalledthe capsule.Lastly,bacterial
surfacescan be coveredbywhip-like extensions:flagellaorpili.Accordingtothe authorsof “Mims
Medical Microbiology,5thEd” (Saunders,2013), longflagellaaidinmotilitywhile shortpilihelpbacteria
to attach to hostsurfaces.
Classification
A fewdifferentcriteriaare usedtoclassifybacteria.Theycan be distinguishedbythe nature of theircell
walls,bytheirshape,orby differencesintheirgeneticmakeup.
The Gram stainisa testusedto identifybacteriabythe compositionof theircellwalls.Itisnamedfor
Hans ChristianGram,whodevelopedthe technique in1884. Bacteriaare firststainedwithapurple dye
calledcrystal violet,whichspecificallybindstopeptidoglycan,acomplex structure of aminoacidsand
sugars foundinthe cell wall.Thisisfollowedbyaseriesof stepsthatultimately remove anyunboundor
looselyboundcrystal violet.
Thenthe cellsare stainedwitha secondred-coloreddye calledsafranin.Gram-positive bacteriastain
purple because theircell wallsare richinpeptidoglycan.Onthe otherhand,Gram-negative bacteria
whose cellswallshave twolayerstake onared coloring.The outerlayerof lipidsdoesnotbindstrongly
to crystal violetandthe dye iseasilywashedawayduringthe stainingprocess.Forexample,
Streptococcuspneumoniae,whichcausespneumonia,isa Gram-positive bacterium, while Escherichia
coli (E.coli) andVibriocholerae,whichcausescholera,are Gram-negativebacteria.
There are three basicbacterial shapes,accordingto“MimsMedical Microbiology.”Roundbacteriaare
referredtoas cocci (singular:coccus);cylindrical,capsule-shapedbacteriaasbacilli (singular:bacillus);
and spiral bacteriaare aptlycalledspirilla(singular:spirillum).Cocci canalso associate withone another
indifferentconfigurations:combinationsof twoordiplococcus;a linearchainorstreptococcus;and a
clusteror staphylococcus.The shapesandconfigurationsof bacteriaare oftenreflectedintheirnames.
For example,the milk-curdlingLactobacillusacidophilusare bacilli,andpneumonia-causing
Streptococcuspneumoniaeare achain of cocci.
The classificationcriteriamentionedthusfarare basedonphysiologicalpropertiesandmorphology.
However,classificationof bacteriabasedontheirevolutionaryrelationshipstoone another,thatisto
say,drawinga sort of familytree of all bacterial species,isarelativelynew development.Thistype of
phylogeneticclassificationbecame possible withthe adventof nucleotide sequencingtechnology(the
abilitytoreadthe order of nucleotidesinDNA orRNA).Since ribosomesare presentinall living

6. organisms,one canlookat similaritiesanddifferencesinthe RNA sequencesthatencode certain
ribosomal proteinsanddeterminethe degreeof relatednessof differentorganisms.
In hisessay,“HowWe Do, Don’tand ShouldLookat Bacteriaand Bacteriology,”includedin“The
Prokaryotes,3rdEd, Vol.1” (Springer,2006) Carl Woese notesthatsequencingribosomal RNA (rRNA)
allowedforthe developmentof a“clearconceptof a bacterium”byestablishingphylogenetic
relationshipsbetweenbacterial species.UsingearlysequencingtechnologydevelopedbyFrederick
Sangerin the mid-1960s, Woese begantocharacterize bacterial rRNA anddiscoveredasecondgroupof
prokaryoticorganismscalledarchaea.Until then,the onlyknownmembersof thisgroup,the
methanogens,hadbeenmistakenlyidentifiedasbacteria.Intheir1977 paper publishedinPNAS,
authorsWoese andGeorge Fox state that methanogensbore “nophylogeneticresemblance”to
bacteria.
Reproduction
Most bacteriamultiplybyaprocesscalledbinaryfission.A single bacterialcell,the “parent,”makesa
copy of itsDNA and growslarge insize bydoublingitscellularcontent.The doubledcontentsare pushed
out to eitherendof the cell.Thenasmall fissure emergesatthe centerof the parent,eventually
splittingitintotwoidentical “daughter”cells.Some bacterial speciessuchascyanobacteriaand
firmicutesreproduceviabudding.Duringbudding,the daughtercell growsasan offshootof the parent.
It starts off as a small nub,growsuntil itis the same size asits parent,andsplitsoff.
The DNA foundinparentsandoffspringafterbinaryfissionorbuddingisexactlythe same.Therefore
bacterial cellstryto introduce some variationintotheirgeneticmaterial byintegratingadditional DNA
intotheirgenome.Thisisknownashorizontal gene transfer,andthe resultinggeneticvariationensures
that bacteriacan adapt and survive astheirenvironmentchanges.There are three waysbywhichthis
occurs: transformation,transductionandconjugation.
Duringtransformation,bacterial cellsintegrate shortfragmentsof DNA fromtheirsurrounding
environment.Accordingtothe authorsof “Mims Medical Microbiology,”these fragmentsmaybe
releasedbynearbybacteriathathave ruptured.Onthe otherhand,transductionoccurswhenbacteria
are infectedbyspecial virusesknownasbacteriophagesthatcan carry bacterial DNA.
Conjugationrequiresphysical contactbetweentwobacteria.Geneticmaterial,usuallyaduplicated
plasmid, will transferfromadonorto a recipient.Thisplasmidcopytravelsoutthroughaphysical
extensioncalledthe pilusandentersthe recipientbacterialcell.Donorbacteriacontainasequence of
DNA calledthe F-factorthat enablespilusformation.Conjugationcanaidinthe spreadof antibiotic
resistance genes.
Bacteria in human health and disease
Bacteriacan be beneficial aswell asdetrimental tohumanhealth.Commensalbacteria,whichshare
space and resourceswithinourbodies,tendtobe helpful. Ina2012 article inthe journal Nature,titled
“LearningAboutWhoWe Are,”DavidA. Relman,amicrobiologistatStanfordUniversity,statesthat

7. there are about 10 timesmore microbial cellsthanhumancellsinthe humanbody.The highest
numbersof microbial speciesare foundinthe gut.
The human gut isa comfortable settingforbacteria,withplentyof nutrientsavailable fortheir
sustenance.Ina2014 reviewarticle,“Analyzingthe HumanMicrobiome:A ‘How To’ Guide for
Physicians,”inthe AmericanJournal of Gastroenterology,the authorsmentionthatgutbacteriaand
othermicroorganismsaidindigestion,stave off colonizationbyharmful pathogens,andhelpinthe
developmentof the immune system.Moreover,the disruptionof gutbacteriahasbeenlinkedtocertain
disease conditions.Forinstance,patientswithCrohn’sdisease have increasedantibodiesagainsttheir
gut bacteriaand theirT-cellsare quite aggressive towardbacterialantigens,accordingtothe authorsof
“Gut Flora inHealthand Disease,”publishedinThe Lancetjournal in2003.
Otherbacteriacan cause infections.Forexample,Streptococcuspneumoniae causespneumonia.
Several bacteriarangingfromgroupA Streptococcus,Clostridium,Escherichiacoli andStaphylococcus
aureuscan cause a rare butsevere softtissue infectioncallednecrotizingfasciitissometimescalled
“flesh-eatingbacteria.”Accordingtothe CentersforDisease Control,thisinfectionaffectsthe tissues
surroundingmuscles,nerves,fat,andbloodvesselsbutitcan be treated,especiallywhencaughtearly.
Antibiotic-resistantstrainsof Staphlyococcusaureusbacteria(purple) have becomethe mostcommon
cause of skininfectionsseeninhospital emergencydepartments.
Antibiotic resistance
Antibioticsare typically usedtotreatbacterial infections.Howeverinrecentyears,the improperor
unnecessaryuse of antibioticshaspromotedthe spreadof several strainsof antibiotic-resistant
bacteria.
Antibioticresistance isaphenomenonwhere infectiousbacteriaare no longersusceptible topreviously
effectiveantibiotics.Accordingtothe CDC,each yearinthe UnitedStates,atleast2 millionpeople are
infectedwithantibioticresistantbacteria,leadingtothe deathof at least23,000 each year.“Pretty
much anyinfectionyoucanthinkof now hasbeenidentifiedasbeingassociatedwithsomelevel of
resistance,”saidDr.ChristopherCrnich,aninfectiousdisease physicianandhospital epidemiologistat
the Universityof WisconsinHospitalsandMadisonVeteransAffairsHospital.“There’sveryfew
infectionsthatwe nowtreatwhere infectionscausedbyresistantbacteriaisnota clinical concern.”
One of the more notoriousantibioticresistantbacterialstrainsismethicillin-resistantStaphylococcus
aureus(MRSA),whichresistsmethicillinandotherantibioticsusedtotreatStaphylococcusinfections.It
spreadsprimarilythroughskincontact.MRSA infectionsoccurinhealthcare settingssuchas hospitals
and nursinghomes,where itcanleadtopneumoniaorbloodstreaminfections.MRSA alsospreadsin
the community,especiallyinsituationswherethere isalotof skincontact or the use of shared
equipment;forexample,amongathletes,intattooparlors,orinday care facilitiesandschools.
Community-acquiredMRSA mostoftencausesskininfections.

8. An importantfacetof combatingantibioticresistance istobe careful abouttheiruse.“It’ssoimportant
for usto use antibioticsintelligently,”CrnichtoldLiveScience.“Youonlywanttouse an antibioticwhen
youhave a clearcut bacterial infection.”
A short history of bacteriology
Some people hadsuggestedthousandsof yearsagothatsomethingtoosmall forthe nakedeye tosee
may be the cause of disease.Overthe hundredsof yearsthatfollowedvarioustheories weregiven.It
was notuntil 1676 that bacteriawere properlyidentifiedasmicroorganisms.Below isashortsynopsisof
some of the mostfamousscientists/microbiologistsinhistory:
Marcus Terentius Varro
a prolificauthor.He suggestedthatdisease maybe causedbyminisculeanimalsthatfloatedinthe air.
He isadmiredbymany scientiststodayforhisanticipationof microbiology(the studyof microorganisms
and theireffectsonotherlivingorganisms) andepidemiology(thestudyof the causes,distribution,and
control of disease inpopulations).He believedmarshyplacesshouldbe avoidedduringbuildingwork
because theymightcontaininsectstoosmall forthe eye tosee that enteredthe bodythroughthe
mouthand nostrilsandcause diseases.
Hippocrates
a physician,consideredone of the mostoutstandingfiguresinthe historyof medicine.He wasthe first
physiciantoseparate medicinefromsuperstition.He saiddiseasewasnota punishmentmetedoutby
gods,but rathera resultof lifestyle,dietandenvironmentalfactors.However,Hippocrates’theorieson
diseasesbeinganimbalance of the fourhumorspresentinthe humanbody,causedbymiasmas –
vaporsfrom rottingvegetablesorbodies,pollutedriversandmarshyplaces – were slightlywiderof the
mark than we knowabouttoday.
Jacobo Forli and Alexandro Benedetti (Italian c. 14th/15th century)
theysaidit wasnot possible togetill justbybreathinginthe air.Theysaidparticlesthatfloatedinthe
air may cause disease if theywere breathedin.
Nevertheless,the MiasmaTheoryperseveredforalongtime,rightfromthe firstcenturythroughto
about1500, whenthe Germ Theorystartedto develop:
Antonie van Leeuwenhoek(Dutch 1632-1723)
he handcraftedsingle-lensmicroscopeshimself,withwhichhe saw whathe calledanimalculesin1676
(tobe calledbacteria162 yearslater).Ina seriesof letterstothe Royal Society(England) he published
hisfindings.He iscommonlyknownasthe fatherof microbiologyandconsideredtobe the first
microbiologist.
ChristianGottfriedEhrenberg(German1795-1876)

9. one of the most famousandprolificscientistsduringthe nineteenthcentury,introducedthe term
bacteriumin1838.
Louis Pasteur (French– 1822 – 1895)
a remarkable chemistwhobecame famous formanybreakthroughsinthe causesandpreventionsof
disease.He createdthe firstvaccine forrabies.Pasteurdemonstratedin1859 that the fermentation
processiscausedby the growthof microorganisms,andnotspontaneousgeneration.He andRobert
Koch,saidthat diseaseswere causedbygerms(The GermTheory).
Robert Koch (German– 1843-1910)
a brilliantphysician/researcherwhowasawardedthe Nobel Prizein1905 afterhe provedThe Germ
Theory.
Paul Ehrlich (German– 1854-1915)
a scientistwhobecame aworldauthorityinimmunology.He inventedthe termchemotherapy.He
developedthe firstantibiotic(Salvarsan) andusedittocure syphilis.He wasawardedthe Nobel Prize in
1908 for hisresearchonimmunology.He pioneeredthe use of stainstodetectbacteria.
Carl Woese (American– 1928-)
currentlyprofessorof microbiologyatthe Universityof IllinoisatUrbana-Champaign.Hiswork
recognizedthatarchaeaevolvedalongaseparate line frombacteria.
Metabolism – How do bacteria feed themselves?
Bacteriafeedthemselvesinavarietyof ways.
Heterotrophicbacteria (or just heterotrophs)
Heterotrophicbacteriaeatotherorganisms.
Most of themare saprobes,theyabsorbdeadorganicmaterial,suchasdecomposingflesh.Someof
these parasiticbacteriakill theirhost,while othershelpthem.
Autotrophic bacteria (or just autotrophs)
Autotrophicbacteriamake theirownfood.
This could be done by photosynthesis
theyuse sunlight,C02,and waterto make theirfood.Bacteriathat use sunlightto synthesize theirfood
are calledphotoautotrophs.These includethe cyanobacteriawhichprobablyplayedavital role in
creatingthe Earth’s oxygenatmosphere.Otherphotoautotraphsdonotproduce oxygen,suchas
heliobacteria,purplenon-sulfurbacteria, purplesulfurbacteria,andgreensulfurbacteria.

10. Others do it by chemosynthesis
theyuse C02, water,andsuch chemicalsasammoniato synthesize theirfood.We call themnitrogen
fixers.Theyare commonlyinlegumerootsandoceanvents.Examplesof legumesare alfalfa,clover,
peas,beans,lentils,andpeanuts.Thesebacteriaare knownaschemoautotrophs.Otherchemicalsused
for nutritionare nitrogen,sulfur,phosphorous,vitamins,andsuchmetallicelementsassodium,
potassium,calcium,magnesium, manganese,iron,zinc,andcobalt.
What kinds of environments dobacteriainhabit?
Aerobes(aerobicbacteria)
these can growonlyin the presence of oxygen.Some typesmaycause seriousproblemstopeople’s
infrastructure astheycan cause corrosion,fouling,problemswithwaterclarity,andbadsmells.
Anaerobes(anaerobicbacteria)
these can onlygrowif there isno oxygenpresent.Inhumans,theyare mostcommonlyfoundinthe
gastrointestinal tract.Theyalsocause gas gangrene,tetanus,andbotulism.Mostdental infectionsare
causedby thistype of bacterium.
Facultative anaerobes (facultative anaerobicbacteria)
these thrive inenvironmentswithorwithoutoxygen.However,whengivenbothoptions,theypreferto
use oxygenforrespiration.Mostcommonlyfoundinsoil,water,vegetationandsome normal floraof
humansand animals.Anexampleof afacultative anaerobicbacteriumissalmonella.
Mesophile (mesophilicbacteria)
these thrive inmoderate temperatures.Examplesinclude Listeriamonocytogenes,Pesudomonas
maltophilia,Thiobacillusnovellus,Staphylococcusaureus,Streptococcuspyrogenes,Streptococcus
pneumoniae,Escherichiacoli,andClostridiumkluyveri.Humanbacterial infectionsare mainlycausedby
mesophilicbacteria–thisis because the bodyof a humanis moderate (37 Celsius).The humanintestinal
floracontainsmanybeneficialmesophilicbacteria,suchasdietaryLactobacillusacidophilus.
Extremophiles(extremophilicbacteria)
these thrive inconditionsconsideredtooextreme formostlife forms,includingmankind.There are
several differenttypesof extremophilicbacteria,dependingonwhatkindof extremestheycantolerate:
 Thermophiles(thermophilicbacteria) –these thrive intemperaturesabove 55Celsius,andcan
tolerate upto 75-80 Celsius.Theytake longertodestroyinboilingwaterthanotherbacteria.
The bacteriaPyrolobusfumarii cantolerate temperaturesupto113 Celsius –it isclassedas a
hyperthermophile.

11.  Halophiles(halophilicbacteria) –these onlythrive in asaltyenvironment,suchassaltine lakes.
An example isHalobacteriacea.
 Acidophiles(acidophilicbacteria) –these onlythrive inacidicenvironments.Cyanidium
caldarium,andFerroplasmaspcan tolerate anenvironmentwithanacidityof pH 0.
 Alkaliphiles(alkiliphilicbacteria) –these onlythrive inalkalineenvironments.Natronobacterium,
BacillusfirmusOF4,andSpirulinasppcanall tolerate upto pH 10.5.
 Psychrophiles(psychrophilicbacteria) –these thrive atverylow temperatures,suchasin
glaciers.Anexample isPsychrobacter.
How bacteria reproduce
Bacteriamay reproduce usingthe followingmethods:
Binary fission
Thisis knownasan asexual formof reproduction;itdoesnotinvolve amale andfemale.The cell
continuesgrowingandgrowing, eventuallyanew cell wall growsthroughthe centerformingtwo
daughtercells,whicheventuallyseparate.Eachdaughtercell hasthe same geneticmaterial asthe
parentcell.
Bacterial recombination
The problemwithbinaryfissionisthateverydaughter cellisidentical tothe cell itcame from, as well as
all itssisters.Thismakesitharderfor bacteriato prevail,especiallyif we attackthemwithantibiotics.To
getaround this,bacteriause a processcalledrecombination.Bacterialrecombinationis achieved
through:
Conjugation
thissimplymeanspassingpiecesof genesfromone bacterial celltoanotherone whentheycome in
contact. A bacteriumconnectsitself toanotherthrougha tube structure calledpilus(there are lotsof
them,spikythings, plural:pilli),youcansee theminthe secondillustrationinthisarticle (scrollup).
Genesfromone bacterial cell gothroughthistube intothe othercell.
Transformation
some bacterial cellscangrab DNA formthe environmentaroundthem –oftenDNA fromdeadbacterial
cells.The bacterial cell bindsthe DNA andcarriesitacross the bacterial cell membrane.Putsimply,it
pullsthe DNA infrom outside throughitscell wall.
Transduction
bacteriagetinfectedbyvirusescalledbacteriophages.The bacteriophageinsertsitsgenome intothe
bacteriumwhenitattachesitself tothe bacterial cell.The genomeof thisvirus,enzymesand
componentsof the virusare replicatedandassembledinside the hostbacterium.The newlyformed
bacteriophagesthencause the rupture ordisintegrationof the bacterial cell wall,resultinginthe release

12. of the replicatedviruses.Sometimes,however,some of the bacterium’sDNA canbecome encasedin
the viral capsid(proteinshell thatsurroundsavirusparticle) insteadof the viral genome duringthe
assemblyprocess.Whenthisbacteriophage goesandinfectsanotherbacteriumitinjectsDNA
fragmentsfromitsprevioushost(the firstbacterium),whichthenbecomesinsertedintothe DNA of the
newbacterium.We call thisgeneralizedtransduction.
Put simply –transductioniswhenavirusgets intothe bacterium, picksupsome of itsDNA,and then
placesitin the nextbacteriumitgetsinto.
ResearchersatTexasA&MUniversity’sArtie McFerrinDepartmentof Chemical Engineeringsuggestthat
geneticmaterial isn’treallycapturedasmuchas itis simplyutilizedafterit’sinjectedintothe bacteria
by an invadingvirus.
Anotherformof transductionisspecializedtransduction.Fragmentsof the firstbacterium’sDNA
become incorporatedintothe viral genomeof the new bacteriophage.These DNA fragmentsare then
transferredtothe nextbacteriumthe bacteriophage infects.
Restingstage – spores
Thisis more a form of hibernationthanreproduction.Whenbacteriadonothave enough resourcesthey
can reproduce byformingspores,whichholdthe organism’sDNA material.
These sporesare alive butnotactive.Whenconditionsare appropriate the sporesbecomenew
bacteria.Sporescan remaindormantforcenturiesbefore becomingnew bacteria.The mainfunctionof
these sporesistosurvive throughperiodsof environmental stress.Theyare resistanttoultravioletand
gamma radiation,desiccation,starvation,chemicalsandextremesof temperature.Somebacteria
produce endospores(internal spores)while othersproduce exospores(releasedoutside)orcysts.The
spore containsenzymeswhichare involvedingermination.
An example of anendospore-formingbacteriumisClostridium,whichconsistsof about100 speciesthat
include commonfree-livingbacteriaaswell asimportanthumandiseasecausingbacteria,suchas
botulism(C.botulinim) andpseudomembranouscolitis(C.difficile).
The effectsofbacteria
Most people tendtoimagine negative thingswhenaskedaboutbacteria.Itisimportantto remember
that bacteriaare soubiquitous,andhave beenaroundsolong – since the beginningof lifeonearth,in
fact – thatwe wouldnothave existedwithoutthem.The airwe breathe – specificallythe oxygeninthe
air we breathe – was mostprobablycreatedmillionsof yearsagobythe activityof bacteria.
Nitrogenfixation
Bacteriaassimilate atmosphericnitrogenandthenreleaseitforplantuse whentheydie.Plantscannot
extractnitrogenfromthe air andplace it inthe soil – butplantsneednitrogeninsoil tolive –without
the bacteriadoingthiswouldnotbe able to carry out a vital partof theirmetabolism.The relationship

13. betweenplantandbacteriahasbecome soclose inthissense thatmanyplantseedshave a small
containerof bacteriathat will be usedwhenthe plantsprouts.
Humans needbacteria to survive
The human bodycontainshuge amountsof friendlybacteriathatare eitherneutral orhelpussomehow.
Bacteriain the digestivesystemare crucial forthe breakdownof certaintypesof nutrients,suchas
complex sugars,intoformsthe bodycan use.Friendlybacteriaalsoprotectusfromdangerousonesby
occupyingplacesinthe bodythe pathogenic(disease causing)bacteriawantattachto. Some friendly
bacteriaactuallycome to the rescue and attack the pathogens.
Bacteria and the ‘obesityepidemic’
Accordingto a studyreleasedbythe International &AmericanAssociationforDental Research,bacteria
may be a contributoryfactorin today’sobesityexplosion.
Effectof bacteriaas pathogensto humans(causesof diseases)
Some of the mostdeadlydiseasesanddevastatingepidemicsinhumanhistoryhave beencausedby
bacteria.
Smallpox andmalaria– notcausedby bacteria– have killedmore humansthanbacterial diseases.
However,the followingbacterial diseaseshave destroyedhundredsof millionsof humanlives:
 Cholera
 Diphtheria
 Dysentery
 Plague
 Pneumonia
 Tuberculosis
 Typhoid
 Typhus.
In the year1900 pneumonia,tuberculosisanddiarrheawere the three biggestkillersinthe USA.As
waterpurificationimproved,vaccinesandimmunizationprogramsevolved,andantibiotictreatment
became more advanced – the humandeathtoll in the USA frombacterial diseaseshasdropped
significantly(aswellasinthe rest of the developedworld).Indevelopingcountries,successrateshave
dependedonseveralfactors,suchasthe strategiesimplementedbylocal healthauthorities,and
whethercountriesenjoyedperiodsof peacetime (nowars).CountriessuchasMexico,Argentina,and
Uruguay, tomention buta few,have alsoseensignificantfallsinbacterial relateddeathsoverthe last
100 years.
Significance of bacteria in food technology

14. Lactic acid bacteria,suchas LactobacillusandLactococcus togetherwithyeastandmolds(fungi) have
beenusedforthe preparationof suchfoodsas cheese,soysauce,vinegar,yoghurtandpickles.Humans
have beenusingthese bacteriaforpreparingfermentedfoodsforthousandsof years.
Significance of bacteria in other technologies
Bacteriacan breakdownorganiccompoundsat remarkable speedandhelpusinour waste processing
and bioremediationactivities.Bacteriaare frequentlyusedforcleaningupoil spills.Theyare usefulin
clearinguptoxicwaste.
The pharmaceutical andchemical industriesuse bacteriain the productionof certainchemicals.They
are usedinthe molecularbiology,biochemistryandgeneticresearchbecausetheycangrow quicklyand
are relative easytomanipulate.Scientistscanuse bacteriato studythe functionsof genesandenzymes,
as well asbacterial metabolicpathways,andthentestouttheirresultsonmore complex organisms.
Such bacteriaas Bacillusthuringiensis(BT) canbe usedinagriculture insteadof pesticides,withoutthe
undesirableenvironmentalconsequencesthatpesticide use maycause.
ScientistsfromUniversityCollegeLondoncreatedanarsenicbiosensorfromlivingbacteria.
For more informationvisitusourwebsite:http://www.healthinfi.com