Medical Microbiology

GeneralCharacteristicsofFungi 351

Metabolism

Allfungiarecarbonheterotrophs,whichmeanstheyaredependentonexo-

genousnutrientsubstratesassourcesoforganiccarbon,andwithafewex-

ceptions,fungiareobligateaerobes.Manyspeciesarecapableofmaintaining

metabolicactivityinthemostbasicofnutrientmediums.Theknownmeta-

bolictypesoffungiincludethermophilic,psychrophilic,acidophilic,andha-

lophilicspecies.Themetaboliccapabilitiesoffungiareexploitedinthefood

industry(e.g.,intheproductionofbread,wine,beer,cheese,orsingle-cell

proteins)andinthepharmaceuticalindustry(e.g.,intheproductionofanti-

bioticsubstances,enzymes,citricacid,etc.).Themetabolicactivityoffungi

canalsobeadamagingfactor.Fungalinfestationcandestroyfoods,wooden

structures,textiles,etc.Fungialsocausenumerousplantdiseases,inpartic-

ulardiseasesofcrops.

ReproductioninFungi

Asexualreproduction.Thiscategoryincludesthevegetativepropagationof

hyphaeandyeastsaswellasvegetativefructification,i.e.,formationofasex-

ualspores.

&Hyphaeelongateinazonejustshortofthetipinwhichthecellwallis

particularlyelastic.Thisapicalgrowthprocesscanalsoincludeformationof

swellingsthatdevelopintolateralhyphae,whichcaninturnalsobranchout.

&Yeastsreproducebybudding.Thisprocessbeginswithanoutgrowthon

themothercellwallthatdevelopsintoadaughtercellorblastoconidium.The

isthmusbetweenthetwoisfinallycutoffbyformationofaseptum.Some

yeastspropagateinboththeyeastandhyphaforms(Fig.6. 2 ,p.362).

&Vegetativefructification.Atypeofpropagativeform,theasexualspores,

isformedinthisprocess.Thesestructuresshowconsiderableresistanceto

exogenousnoxaeandhelpfungispreadinthenaturalenvironment.Asexual

sporescomeinanumberofmorphologicaltypes:conidia,sporangiospores,

arthrospores,andblastospores.Theseformsrarelydevelopduringthepara-

siticstagesinhosts,buttheyareobservedincultures.Themorphologyofthe

asexualsporesoffungiisanimportantidentificationcharacteristic.

Sexualfructification.Sexualreproductioninfungiperfecti(eumycetes)fol-

lowsessentiallythesamepatternsasinthehighereukaryotes.Thenucleiof

twohaploidpartnersfusetoformadiploidzygote.Thediploidnucleusthen

undergoesmeiosistoformthehaploidnuclei,finallyresultinginthehaploid

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Kayser, Medical Microbiology © 2005 Thieme