04Nutrition and Growth of Bacteria.docx
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04NutritionandGrowthofBacteria
NutritionandGrowthofBacteria(page1)
(Thischapterhas6pages)
©2011KennethTodar,PhD
NutritionalRequirementsofCells
Everyorganismmustfindinitsenvironmentallofthesubstancesrequiredforenergygenerationandcellularbiosynthesis.Thechemicalsandelementsofthisenvironmentthatareutilizedforbacterialgrowtharereferredtoasnutrientsornutritionalrequirements.Manybacteriacanbegrownthelaboratoryinculturemediawhicharedesignedtoprovidealltheessentialnutrientsinsolutionforbacterialgrowth.Bacteriathataresymbiontsorobligateintracellularparasitesofothercells,usuallyeucaryoticcells,are(notunexpectedly)difficulttogrowoutsideoftheirnaturalhostcells.Whetherthemicrobeisamutualistorparasite,thehostcellmustultimatelyprovidethenutritionalrequirementsofitsresident.
Manybacteriacanbeidentifiedintheenvironmentbyinspectionorusinggenetictechniques,butattemptstoisolateandgrowtheminartificialculturehasbeenunsuccessful.This,inpart,isthebasisoftheestimatethatwemayknowlessthanonepercentofallprocaryotesthatexist.
TheMajorElements
Atanelementarylevel,thenutritionalrequirementsofabacteriumsuchasE.coliarerevealedbythecell'selementalcomposition,whichconsistsofC,H,O,N,S.P,K,Mg,Fe,Ca,Mn,andtracesofZn,Co,Cu,andMo.Theseelementsarefoundintheformofwater,inorganicions,smallmolecules,andmacromoleculeswhichserveeitherastructuralorfunctionalroleinthecells.ThegeneralphysiologicalfunctionsoftheelementsareoutlinedinTable1.
Table1.Majorelements,theirsourcesandfunctionsinbacterialcells.
Element
%ofdryweight
Source
Function
Carbon
50
organiccompoundsorCO2
Mainconstituentofcellularmaterial
Oxygen
20
H2O,organiccompounds,CO2,andO2
Constituentofcellmaterialandcellwater;O2iselectronacceptorinaerobicrespiration
Nitrogen
14
NH3,NO3,organiccompounds,N2
Constituentofaminoacids,nucleicacidsnucleotides,andcoenzymes
Hydrogen
8
H2O,organiccompounds,H2
Mainconstituentoforganiccompoundsandcellwater
Phosphorus
3
inorganicphosphates(PO4)
Constituentofnucleicacids,nucleotides,phospholipids,LPS,teichoicacids
Sulfur
1
SO4,H2S,So,organicsulfurcompounds
Constituentofcysteine,methionine,glutathione,severalcoenzymes
Potassium
1
Potassiumsalts
Maincellularinorganiccationandcofactorforcertainenzymes
Magnesium
0.5
Magnesiumsalts
Inorganiccellularcation,cofactorforcertainenzymaticreactions
Calcium
0.5
Calciumsalts
Inorganiccellularcation,cofactorforcertainenzymesandacomponentofendospores
Iron
0.2
Ironsalts
Componentofcytochromesandcertainnonhemeiron-proteinsandacofactorforsomeenzymaticreactions
TraceElements
Table1ignorestheoccurrenceoftraceelementsinbacterialnutrition.Traceelementsaremetalionsrequiredbycertaincellsinsuchsmallamountsthatitisdifficulttodetect(measure)them,anditisnotnecessarytoaddthemtoculturemediaasnutrients.Traceelementsarerequiredinsuchsmallamountsthattheyarepresentas"contaminants"ofthewaterorothermediacomponents.Asmetalions,thetraceelementsusuallyactascofactorsforessentialenzymaticreactionsinthecell.Oneorganism'straceelementmaybeanother'srequiredelementandvice-versa,buttheusualcationsthatqualifyastraceelementsinbacterialnutritionareMn,Co,Zn,Cu,andMo.
CarbonandEnergySourcesforBacterialGrowth
Inordertogrowinnatureorinthelaboratory,abacteriummusthaveanenergysource,asourceofcarbonandotherrequirednutrients,andapermissiverangeofphysicalconditionssuchasO2concentration,temperature,andpH.Sometimesbacteriaarereferredtoasindividualsorgroupsbasedontheirpatternsofgrowthundervariouschemical(nutritional)orphysicalconditions.Forexample,phototrophsareorganismsthatuselightasanenergysource;anaerobesareorganismsthatgrowwithoutoxygen;thermophilesareorganismsthatgrowathightemperatures.
Alllivingorganismsrequireasourceofenergy.Organismsthatuseradiantenergy(light)arecalledphototrophs.Organismsthatuse(oxidize)anorganicformofcarbonarecalledheterotrophsor(chemo)heterotrophs.Organismsthatoxidizeinorganiccompoundsarecalledlithotrophs.
Thecarbonrequirementsoforganismsmustbemetbyorganiccarbon(achemicalcompoundwithacarbon-hydrogenbond)orbyCO2.OrganismsthatuseorganiccarbonareheterotrophsandorganismsthatuseCO2asasolesourceofcarbonforgrowtharecalledautotrophs.
Thus,onthebasisofcarbonandenergysourcesforgrowthfourmajornutritionaltypesofprocaryotesmaybedefined(Table2).
Table2.Majornutritionaltypesofprocaryotes
NutritionalType
EnergySource
CarbonSource
Examples
Photoautotrophs
Light
CO2
Cyanobacteria,somePurpleandGreenBacteria
Photoheterotrophs
Light
Organiccompounds
SomePurpleandGreenBacteria
ChemoautotrophsorLithotrophs(Lithoautotrophs)
Inorganiccompounds,e.g.H2,NH3,NO2,H2S
CO2
AfewBacteriaandmanyArchaea
ChemoheterotrophsorHeterotrophs
Organiccompounds
Organiccompounds
MostBacteria,someArchaea
Almostalleucaryotesareeitherphotoautotrophic(e.g.plantsandalgae)orheterotrophic(e.g.animals,protozoa,fungi).Lithotrophyisuniquetoprocaryotesandphotoheterotrophy,commoninthePurpleandGreenBacteria,occursonlyinaveryfeweucaryoticalgae.PhototrophyhasnotbeenfoundintheArchaea,exceptfornonphotosyntheticlight-drivenATPsynthesisintheextremehalophiles.
GrowthFactors
Thissimplifiedschemeforuseofcarbon,eitherorganiccarbonorCO2,ignoresthepossibilitythatanorganism,whetheritisanautotrophoraheterotroph,mayrequiresmallamountsofcertainorganiccompoundsforgrowthbecausetheyareessentialsubstancesthattheorganismisunabletosynthesizefromavailablenutrients.Suchcompoundsarecalledgrowthfactors.
Growthfactorsarerequiredinsmallamountsbycellsbecausetheyfulfillspecificrolesinbiosynthesis.Theneedforagrowthfactorresultsfromeitherablockedormissingmetabolicpathwayinthecells.Growthfactorsareorganizedintothreecategories.
1.purinesandpyrimidines:
requiredforsynthesisofnucleicacids(DNAandRNA)
2.aminoacids:
requiredforthesynthesisofproteins
3.vitamins:
neededascoenzymesandfunctionalgroupsofcertainenzymes
Somebacteria(e.g.E.coli)donotrequireanygrowthfactors:
theycansynthesizeallessentialpurines,pyrimidines,aminoacidsandvitamins,startingwiththeircarbonsource,aspartoftheirownintermediarymetabolism.Certainotherbacteria(e.g.Lactobacillus)requirepurines,pyrimidines,vitaminsandseveralaminoacidsinordertogrow.Thesecompoundsmustbeaddedinadvancetoculturemediathatareusedtogrowthesebacteria.Thegrowthfactorsarenotmetabolizeddirectlyassourcesofcarbonorenergy,rathertheyareassimilatedbycellstofulfilltheirspecificroleinmetabolism.Mutantstrainsofbacteriathatrequiresomegrowthfactornotneededbythewildtype(parent)strainarereferredtoasauxotrophs.Thus,astrainofE.colithatrequirestheaminoacidtryptophaninordertogrowwouldbecalledatryptophanauxotrophandwouldbedesignatedE.colitrp-
Figure1.Cross-feedingbetweenStaphylococcusaureusandHaemophilusinfluenzaegrowingonbloodagar.©GloriaJ.DelisleandLewisTomalty,QueensUniversity,Kingston,Ontario,Canada.LicensedforusebyASMMicrobeLibraryhttp:
//www.microbelibrary.org.HaemophilusinfluenzaewasfirststreakedontothebloodagarplatefollowedbyacrossstreakwithStaphylococcusaureus. H.influenzaeisafastidiousbacteriumwhichrequiresbothheminandNADforgrowth.ThereissufficienthemininbloodforgrowthofHaemophilus,butthemediumisinsufficientinNAD.S.aureusproducesNADinexcessofitsownneedsandsecretesitintothemedium,whichsupportsthegrowthofHaemophilusassatellitecolonies.
SomevitaminsthatarefrequentlyrequiredbycertainbacteriaasgrowthfactorsarelistedinTable3.Thefunction(s)ofthesevitaminsinessentialenzymaticreactionsgivesacluewhy,ifthecellcannotmakethevitamin,itmustbeprovidedexogenouslyinorderforgrowthtooccur.
Table3.Commonvitaminsrequiredinthenutritionofcertainbacteria.
Vitamin
Coenzymeform
Function
p-Aminobenzoicacid(PABA)
-
Precursorforthebiosynthesisoffolicacid
Folicacid
Tetrahydrofolate
Transferofone-carbonunitsandrequiredforsynthesisofthymine,purinebases,serine,methionineandpantothenate
Biotin
Biotin
BiosyntheticreactionsthatrequireCO2fixation
Lipoicacid
Lipoamide
Transferofacylgroupsinoxidationofketoacids
Mercaptoethane-sulfonicacid
CoenzymeM
CH4productionbymethanogens
Nicotinicacid
NAD(nicotinamideadeninedinucleotide)andNADP
Electroncarrierindehydrogenationreactions
Pantothenicacid
CoenzymeAandtheAcylCarrierProtein(ACP)
Oxidationofketoacidsandacylgroupcarriersinmetabolism
Pyridoxine(B6)
Pyridoxalphosphate
Transamination,deamination,decarboxylationandracemationofaminoacids
Riboflavin(B2)
FMN(flavinmononucleotide)andFAD(flavinadeninedinucleotide)
Oxidoreductionreactions
Thiamine(B1)
Thiaminepyrophosphate(TPP)
Decarboxylationofketoacidsandtransaminasereactions
VitaminB12
Cobalaminecoupledtoadeninenucleoside
Transferofmethylgroups
VitaminK
Quinonesandnapthoquinones
Electrontransportprocesses
CultureMediafortheGrowthofBacteria
Foranybacte
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