Nutrition in Fungi_for Microbiology and Mycology

Fungi

1. NUTRITION IN FUNGI

2. Nutritional requirements in Fungi
➢Fungiareheterotrophicinnutrition
➢Theyarechlorophylldeficientorganisms,hencecannot
manufacturecarbohydrates.
➢Withsimplestructuralorganization,theymostlydependenton
deadorlivingorganicmatterfortheirenergyrequirements
➢AllfungiareCHEMOHETEROTROPHIC (chemo-
organotrophic)-synthesizingtheorganiccompoundstheyneed
forgrowthandenergyfrompre-existingorganicsourcesin
theirenvironment,usingtheenergyfromchemicalreactions

3. •Sincetheirprotoplasmisprotectedbyarigidwall,fungimust
obtaintheirnutrientsbytheprocessofabsorption
•Smallmolecules(e.g.simplesugars,aminoacids)insolutioncan
beabsorbeddirectlyacrossthefungalwallandplasma
membrane
•Larger,morecomplexmolecules(e.g.polymerssuchas
polysaccharidesandproteins)mustbefirstbrokendowninto
smallermolecules,whichcanthenbeabsorbed
•Thisdegradationtakesplaceoutsidethefungalcellorhypha
andisachievedbyenzymeswhichareeitherreleasedthroughor
areboundtothefungalwall
•Becausetheseenzymesactoutsidethecelltheyarecalled
Extracellularenzymes

4. Essential Elements
➢Theseelementswhichfungirequireasfoodaretermedthe
essentialelements
➢Someofthese,thefungineedinextremelysmalltrace
amounts(Microelements)andtheothersincomparatively
largeramounts(macroelements)
➢Theconstituentelementsoftheorganicandinorganic
substanceswhichfungimakeuseofareC,O,H,N,P,K,Mg,
S,P,Mn,Cu,Mo,Fe,ZnandCalcium
➢Themacroelementsarebodybuildersandprovideenergyfor
metabolicprocesses

5. Sources of Macro Elements
➢Theorganicsubstancesusuallyutilizedbyfungiareveryvariedinnature
➢Thecarbohydratesareneededforbuildingupthebodyandalsoasasourceofenergy
➢Yeastsuseacetatesassourcesofcarbonbutformostfungithechiefsourcesofcarbon
arethecarbohydrates(simplesugars)
➢Glucoseissuitableforalmostallfungiandnextinpreferencearethefructoseand
Sucrose
➢Thepolysaccharides,starchandcelluloseareutilisedbyafewerfungiwhichcan
synthesizetheappropriatehydrolyticenzymes
➢Lesscommonlyusedarethehexosesugarsandsomepentoses
➢Mannitolisequivalenttoglucoseformanyfungi
➢Maltosewhichoccursinnatureasabyproductofstarchhydrolysisisutilizedbymany
fungi
➢Basidiomycetesincludemostofthelignin-utilizingfungi
➢Somefungiareabletomakegoodgrowthonfatsastheonlysourceofcarbon
➢Lipids,someorganicacidsandhigheralcoholsareutilizedbysomefungiasasole
energysourceofgrowth

6. ➢Fungirequirenitrogenthroughbothorganicandinorganicmaterials
➢Innature,fungidecomposeproteinsandpeptideoranaminoacidtoobtain
theirsupplyofnitrogen
➢ThemembersofSaprolegniaceaeandBlastocladialesgrowonlywithorganic
nitrogensuchasaminoacid
➢In pure cultures amino acids, peptides, or peptones gelatin, casein and egg
albumin can serve as sources of organic nitrogen for building up protoplasm
➢Urea is also considered as a utilisable nitrogen source for some fungi
➢Many fungi, however, obtain nitrogen from inorganic sources
➢A number of fungi are known which use both nitrate and ammonium salts
(Example: Absidia sp., Mucor hiemalis, Lenzites trabea and Marasmius sp.)
➢Fewer fungi are able to utilize nitrate salts
➢Organicsourcesofnitrogencanalsoserveassourcesofcarbon
➢Soil inhabiting Rhodotorula and yeast-like Pullularia pullans fix atmospheric
nitrogen

7. ➢Hydrogenandoxygenaresuppliedintheformofwaterwhichis
themajorconstituentoffungusmyceliumformingabout85-
90%oftheentireweight
➢Thechiefamongtheinorganicnutrientswhichthefungirequire
infairlylargeamountsfortheirmineralnutritionaresulphur,
phosphorus,potassiumandmacronutrientsthefungiobtain
fromsimpleinorganicsaltsorsourcessuchassuIphatesfor
sulphur,andphosphatesforphosphorus
➢Somefungiarereportedtorequireonlyminutetracesofiron,
zinc,copper,manganeseandcobaltandmolybdenuminanionic
forms

8. ➢Fungiutilizethevitaminsorgrowthfactorsinminute amounts
➢The important fungal vitamins, which may function in enzyme
systems include thiamine (B1), biotin, pyredoxine (B6) and
riboflavin (B2)
➢A few fungi also need nicotinic acid and pantothenic acid
➢The vast majority, however, require thiamine (B1 )

9. Mechanism of Nutrition in Fungi
➢Thewholemyceliummayhavethepowertoabsorbthesenutrientsorthistask
maybeassignedtospecialportionsofthemycelium.
➢Insaprophyticfungithehyphae(Mucormucedo)orrhizodialhyphae(Rhizopus
stolonifer)comeinintimatecontactwithnutrientsinthesubstratumandabsorb
solublesmallermoleculessuchsugarsandaminoacids
➢Insolublecomplexsubstancessuchasproteins,lipidsetc.arefirstbrokeninto
solublemonomers(digested)bysecretingextra-cellularenzymesandthen
absorbed
➢Themyceliumoftheparasitesisrarelyectophyticbutfrequentlyitgrowsinside
thehost.Thehyphaeeitherramifyintheintercellularspacebetweenthehostcells
orpenetrateintothehostcells
➢Theintercellularhyphaeofsomehighlyspecialised(obligate)plantparasitesgive
outslenderlateraloutgrowths

10. •Onthebasisofmodeofnutritionfungiareclassifiedinto
fourgroups
➢Saprophytes
➢Parasites
➢Symbionts
➢Predaceous

11. Saprophytic Fungi
•Saprophyticfungiobtaintheirnutritionfromdeadorganicmatter
•Itmaybebothanimalorplantorigin
•Thevegetativephaseofthisfungidirectlyabsorbnutrition
requiredfortheirgrowth
•Somespeciesbearspecialstructuresforabsorptionofnutrition
calledrhizoids
•Thesefungimainlyproduceexoenzymesforreleaseofsimple
organicmatter
Theymaybeoftwotypes
➢Ectophyticsaprophytes-growonthesurfaceoforganicmatter
➢Endophyticsaprophytes-growinsidetheorganicmatter
Ex.Saprolegnia,Mucor,Rhizopus,Aspergillus,Penicillium,Agaricus
etc.

12. Parasitic fungi
➢Thesefungitakefoodfromotherlivingplantsandanimals
➢Thelivingorganismsonwhichfungigrowarecalledhost
➢Thegrowingfungiareharmfultothehostastheydevelopdiseaseconditionsin
theirhost
➢Suchrelationshipisknownasparasitism
•The parasitic fungi are of three types
➢Obligate parasites-essentially require living host, not able to live on dead organic
matter
Ex. Puccinia, Albugo
➢Facultative Saprophytes-These are parasites but can live on dead organic matter
when specific host is not available
Ex. Taphrina
➢Facultative parasites-These are usually saprophytes but under certain conditions
they parasitized living host
Ex. Fusarium, Phythium

13. •Onthebasisoflocationofparasiticfungiintheirhosttheyare
classifiedas
Ectoparasitic-liveonoutersurfaceofhost(Ex.Erysiphe)
Endoparasitic-growinsidethehosttissue(Ex.Fusarium)
➢Parasiticfungipossessspecializedabsortivestructurescalled
haustoria
➢Haustoriaarespecializedhyphalmidifications
➢Itmaybeintercellularorintracellularinlocation
➢Itssizeandshapevariesindifferentfungalgroups
➢Itmayberound,knoblike,clublikeorbranched
Ex.Erysiphae,Phytophthora,Albugo

14. Symbionts
➢Thesefungigrowonorwithlivingorganismsbutbothofthem
aremutuallybenefitted
Ex.LichenandMycorrhiza
➢Lichensaresymbioticassociationofalgaeandfungi
➢Mycorrhizaaresymbiticassociationoffungiandrootsof
higherplants
➢Itmaybeectorendomycorrizationinlocation

15. Predacious Fungi
➢Theseareanimalcapturingfungi
➢Thefungipossessspecialhyphaltrapscalledsnareswhich
capturesmallanimalslikeamoebaandnematodes
➢Thesefungiusuallyinhabitinthesoil
➢Theypossessrapidconstructinghyphaltrapsandpenetrating
haustoriatofatchnutritionfromtheirprey
➢Someofthemalsoproducestickysecretionsforcapturingtheir
prey
Ex.Arthrobotrys,Dactylaria