Nutritional classification of microorganisms

Nutritional classification of microorganisms for MPM subject

1. Nutritional classification of
Microorganisms
By
Mr. K. VIJAY,
Assistant Professor,
Sacred Heart College,
Tirupattur District.

2. Themaindeterminantsofamicrobe’snutritionaltype
areitssourcesofcarbonandenergy.Inaprevious
section,microbesweredefinedasautotrophs,whose
primarycarbonsourceisinorganiccarbon(CO
2),and
heterotrophs,whicharedependentonorganiccarbon
compounds.
Intermsofenergysource,microbesthat
photosynthesizearegenerallyclassifiedas
phototrophs,andthosethatoxidizechemical
compoundsarechemotrophs.
Thetermsforcarbonandenergysourceareoften
mergedintoasinglewordforconvenience.The
categoriesdescribedherearemeanttodescribeonly
themajornutritionalgroupsanddonotincludeunusual
exceptions.

4. AutotrophsandTheirEnergySources
Autotrophsderiveenergyfromoneoftwopossible
nonlivingsources:sunlight(photoautotrophs)and
chemicalreactionsinvolvingsimpleinorganicchemicals
(chemoautotrophs).
Photoautotrophsarephotosynthetic;thatis,theycapture
theenergyoflightraysandtransformitintochemical
energythatcanbeusedincellmetabolism.
Becausephotosyntheticorganisms(algae,plants,some
bacteria)produceorganicmoleculesthatcanbeusedby
themselvesandheterotrophs,theyformthebasisfor
mostfoodwebs.Theirroleistoactasprimary
producersoforganicmatter

5. Asignificanttypeofbacteriacalledchemoautotrophs
haveanunusualnutritionaladaptationthatrequires
neithersunlightnororganicnutrients.
Some microbiologistsprefertocallthem
lithoautotrophs(rockfeeders)inreferencetotheirtotal
relianceoninorganicminerals.Thesebacteriaderive
energyindiverseandratheramazingways.
Inverysimpleterms,theyremoveelectronsfrom
inorganicsubstratessuchashydrogengas,hydrogen
sulfide,sulfur,orironandcombinethemwithcarbon
dioxide.

6. Thisreactionprovidessimpleorganicmoleculesanda
modestamountofenergytodrivethesynthetic
processesofthecell.
Chemoautotrophicbacteriaplayanimportantpartin
recyclinginorganicnutrients.
Foranexampleofchemoautotrophyanditsimportance
todeep-seacommunities.
Aninterestinggroupofchemoautotrophsare
methanogens,whichproducemethane(CH
4)from
hydrogengasandcarbondioxide.
4H
2+ CO
2→ CH
4+ 2H
2O

7. Methane,sometimescalled“swampgas,”isformedin
anaerobic,hydrogen-containingmicroenvironmentsof
soil,swamps,mud,andevenintheintestinesofsome
animals.
Manymethanogensarearchaeathatliveinextreme
habitatssuchasoceanventsandhotsprings,where
temperaturesreachupto125°C.
Methanecanbeharvestedandusedasaninexpensive
energysourceincertainindustries.

8. Biogasgeneratorsaredevicesprimedwithamixed
populationofmicrobes(includingmethanogens)and
fueledwithvariouswastematerialsthatcansupply
enoughmethanetodriveasteamgenerator.
Methanealsoplaysaroleasoneofthegreenhouse
gasesthatiscurrentlyanenvironmentalconcern.

9. Autotrophicbacteria-Phytosyntheticbacteria
Fewpurplesulphur(e.g.,Chromatium)bacteriapossess
pigments,suchas,purplepigment,thebacteriopurpurin,and
greenpigment,thebacterialchloroyhylletc.
Bacterioviridinoccurshigreensulphurbacteria,e.g.,
Chlorobium.Suchbacteriasynthesizetheircarbohydratefood
inpresenceofsunlightbyphotosynthesisandareknownas
chlorophyllbacteria.

10. Autotrophic bacteria -Chemosynthetic bacteria
These bacteria get their energy for food synthesis from
the oxidation of certain inorganic chemicals. Light
energy is not used.
The energy obtained from the chemical reactions is
exothermic. The Chemosynthetic bacteria are of the
following types:
(a)Sulphomonas(Sulphur bacteria):These bacteria
get their energy by oxidation of hydrogen sulphideinto
H
2SO
4, e.g., Thiobacillus, Beggiatoa.

11. (b)Hydromonas(Hydrogen bacteria):These convert
hydrogen into water, e.g., Bacillus pantotrophus.
(c) Ferromonas(Iron bacteria):These bacteria get
their energy by oxidation of ferrous compounds into
ferric forms,. e.g., Leptothrix.
(d) Methanomonas(Methane bacteria):These
bacteria get their energy by oxidation of methane into
water and carbon dioxide.
(e) Nitrosomonas(Nitrifying bacteria):These bacteria
get their energy by oxidation of ammonia and nitrogen
compounds like nitrites, nitrates. Nitrosomonasoxidises
NH
3to nitrites.
Nitrobacterconverts nitrites to nitrates.

12. HeterotrophsandTheirEnergySources
Themajorityofheterotrophicmicroorganismsare
chemoheterotrophsthatderivebothcarbonandenergy
fromorganiccompounds.Processingtheseorganic
moleculesbyrespirationorfermentationreleases
energyintheformofATP.
Anexampleofchemoheterotrophyisaerobicrespiration,
theprincipalenergyyieldingreactioninanimals,most
protozoaandfungi,andaerobicbacteria.Itcanbe
simplyrepresentedbytheequation:
Glucose[(CH2O)n]+O
2→CO
2+H
2O+Energy(ATP)

13. Chemoheterotrophicmicroorganismsbelongtooneof
twomaincategoriesthatdifferinhowtheyobtaintheir
organicnutrients:Saprobes arefree-living
microorganismsthatfeedprimarilyonorganicdetritus
fromdeadorganisms,andparasitesordinarilyderive
nutrientsfromthecellsortissuesofahost.

14. SaprobicMicroorganisms–
Saprobesoccupyanicheasdecomposersofplantlitter,
animalmatter,anddeadmicrobes.
Ifnotfortheworkofdecomposers,theearthwould
graduallyfillupwithorganicmaterial,andthenutrientsit
containswouldnotberecycled.
Mostsaprobes,notablybacteriaandfungi,havearigid
cellwallandcannotengulflargeparticlesoffood.To
compensate,theyreleaseenzymestotheextracellular
environmentanddigestthefoodparticlesintosmaller
moleculesthatcanpassfreelyintothecell.

15. Obligatesaprobesexiststrictlyonorganicmatterinsoil
andwaterandareunabletoadapttothebodyofalive
host.
Thisgroupincludesmanyfree-livingprotozoa,fungi,and
bacteria.
Apparently,therearefewerofthesestrictspeciesthan
wasoncethought,andmanysupposedlynonpathogenic
saprobescaninfectasusceptiblehost.
Whenasaprobeinfectsahost,itisconsidereda
facultativeparasite.Suchaninfectionusuallyoccurs
whenthehostiscompromised,andthemicrobeis
consideredanopportunisticpathogen.

16. Forexample,althoughitsnaturalhabitatissoiland
water,Pseudomonasaeruginosafrequentlycauses
infectionsinhospitalizedpatients.
TheyeastCryptococcusneoformanscausesasevere
lungandbraininfectioninAIDSpatients,yetitsnatural
habitatisthesoil.

17. Parasitic Microorganisms
Parasitesliveinoronthebodyofahost,whichthey
usuallyharmtosomedegree.Parasitesinclinedto
causedamagetotissues(disease)orevendeathare
calledpathogens.
Parasitesrangefromvirusestohelminthworms,and
theycanliveonthebody(ectoparasites),intheorgans
andtissues(endoparasites),orevenwithincells
(intracellularparasites,themostextremetype).

18. Althoughthereareseveraldegreesofparasitism,the
moresuccessfulparasitesgenerallyhavenofataleffects
andeventuallyevolvetoalessharmfulrelationshipwith
theirhost.
Obligateparasites(forexample,theleprosybacillusand
thesyphilisspirochete)areunabletogrowoutsideofa
livinghost.
Parasitesthatarelessstrictcanbeculturedartificiallyif
providedwiththecorrectnutrientsandenvironmental
conditions.

19. BacteriasuchasStreptococcuspyogenes(thecauseof
strepthroat)andStaphylococcusaureuscangrowon
artificialmediaassaprobes.
Obligateintracellularparasitismisanextremebut
relativelycommonmodeoflife.
Microorganismsthatspendallorpartoftheirlifecycle
insideahostcellincludetheviruses,afewbacteria
(rickettsias,chlamydias),andcertainprotozoa
(apicomplexa).
Contrarytowhatonemightthink,theinsideofacellis
notcompletelywithouthazards,andmicrobesmust
overcomesomedifficultchallenges.

20. Obligateintracellularparasitismisanextremebut
relativelycommonmodeoflife.
Microorganismsthatspendallorpartoftheirlifecycle
insideahostcellincludetheviruses,afewbacteria
(rickettsias,chlamydias),andcertainprotozoa
(apicomplexa).
Contrarytowhatonemightthink,theinsideofacellis
notcompletelywithouthazards,andmicrobesmust
overcomesomedifficultchallengestoinfectothercells.

21. Intracellularparasitesobtaindifferentsubstancesfrom
thehostcell,dependingonthegroup.
Virusesarethemostextreme,parasitizingthehost’s
geneticandmetabolicmachinery.
Rickettsiasareprimarilyenergyparasites,andthe
malariaprotozoanisahemoglobinparasite.