11thenvironmental Factors of Fungal Growth

8/16/2019 11thenvironmental Factors of Fungal Growth

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The major environmentalefects are:

Temperature

Optimal pHOxygen requirementWater availability

Light


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Fungi can be divided into groups accordingto temperature requirements or optimalgro!th"

#" $sychrophile %cold&loving'

&optimum gro!th not more than #()*and maximum gro!th +,)*

&environment : polar and alpine region & Clasdosporium herbarum,

Thamnidium elegans


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+" -esophiles&most ungi is mesophilic

&optimum in the room temperature !ith range%#,&.,)*'& Aspergillus favus, Penicillium chrysogenum

/" Thermophiles %heat&loving'&optimum& .,)*&0,)*

&*an gro! at temperatures that !oulddenature 1ey proteins in most organisms%typically 0,)*'2up to and including thetemperature o !ater boiling at sea level"

&Thermomyces lanuginosus, Chaetomium thermophile


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There are a range o chemical actorscontribute to temperature tolerance in ungi

The ability to gro! in the more extreme

environment involves adaptation o !holemicroorganisms

The temperature limits set by the 3rstcellular component or process thatbrea1do!n"


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The lo!er temperature limits are set by theollo!ing actors:

#" reduced rate o chemical reaction at lo!temperature

+" The increased o viscosity o cellular !aterat sub4ero temperatures

/"5xcessive concentration o cellular ionsleading to protein inactivation


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6obinson%+,,#' states that 7the lo!ergro!th temperature o psycrophiles is3xed2not by the cellular properties ocellular macromolecules2 but instead by thephysical properties o aqueous solventsystems inside and outside o the cell 8"


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• From studies on bacteria2 yeast and3lamentous ungi2 changes in temperature

lead to changes in atty acid composition othe membrane lipids"• To ensure that membrane 9uidity is optimal

or the unctioning o membrane transporter

and en4ymes & term o homeoviscousadaptation.


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5xamples o homeoviscous adaptation"

%i'The atty acids and membranephospholipids o certain psychrophilic yeast

and 3lamentous ungi are more unsaturatedthan in mesophiles and degree o

unsaturation increased at lo!ertemperature"

%;aturated atty acids are less 9uid thanunsaturated atty acid at any given

temperature'• 5g:& Monographella nivalis %sno! mold'


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%ii'High concentration o disaccharide

trehalose oten occur in psychrophilic andpsychrotrophic ungi in response to lo!temperatures

&Trehalose acts as general stress protectant%in cytosol' !hereby it stabili4ed membraneduring dehydration"

&


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%iii' The en4ymes and ribosomal components

o thermophilic yeast be more heat stablethan those o mesophiles"

& the heat stability is conerred by increasedbonding bet!een the amino acids near the

en4yme active site"&the heat stabili4ing actors %in cytosol' also

contribute to the thermostability oen4ymes"


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◦ pH range: The gro!th o the majority o bacteria

usually over pH range .",&="0

pH range classi3cations include: >cidophile %pH ? 0".'

&coal reuse tips2 acidic mines !astes

& Acontium velatum


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@eutrophile %pH 0". & ="0'

-ost human pathogens areneutrophiles2 !hich have optimal pH A"

>l1aliphile %pH A", & ##"0' ;oda la1es and al1aline springs

Vibrio cholerae, Chladosporium


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• The ungi that have gro! at extremes o pH

are ound to have an internal2cytosolic pH oabout pH A"

• BtCs suggest that ungal cytosol has strongbufering capacity" 5ven !hen external cellular

pH is changed by several units2 the cytosolicpH changes at most ,"+ & ,"/ units"• This could be achieved by several !ays:&


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a'


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•


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◦ There are many degrees o oxygenrequirement among microorganisms2described as:

aerobes

obligate aerobes

acultative aerobes

microaerophiles anaerobes

obligate anaerobes


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• Aerobes & microorganism that can utili4emolecular oxygen as its 3nal electron acceptor2e"g as in cellular %aerobic' respiration"

• Obligate aerobes & organisms that

are able to gro! in the presence oatmospheric oxygen concentrations

gro!th is reduced i partial pressure ooxygen is lo!ered"

use O+ as a 3nal electron acceptor

cannot erment i no oxygen"

Armillaria mellea


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Facultative aerobes & microorganismthat gro! in aerobic conditions but alsocan gro! in the absence o oxygen byermenting sugars"

5nergy yield rom ermentation muchlo!er than aerobic ermentation" Mucor hiemalis, Aspergillus umigatus

Microaerophiles & microorganisms !hich

are unable to gro! !hen oxygenconcentrations reach those ound in air%+,G' but nevertheless !hose gro!threquires the presence o some oxygen


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•

Anaerobes & microorganism that need notutili4e molecular oxygen as a 3nal electronacceptor 2 in order to produce >T$"

• Obligate anaerobes & microorganismthat is 1illed by exposure to oxygen"

• Live as part o an intimate and complex

microbial community2 or consortium inanimalCs oregut %rumen'"

• -embers o *hytridiomycota"


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The

physiologyo oxygentolerance


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• The existence o strictly anaerobic organismssuch as rumen chytrids and ciliated proto4oaindicates that oxygen can be toxic E it 1ills

these organism !hen they are exposed toeven a lo! level o oxygen"

• ;everal highly reactive orms o oxygen such

as superoxide anion2 hydrogen peroxide andhydroxyl radical are produced inadvertently!hen oxygen reacts !ith some cellularconstituents such as 9avoprotein and

quinones"

• These reactive oxygen species !oulddamaged cellular components"


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• >ll organism need certain mechanism orcoping !ith the toxic efect o oxygen in orderto gro! in the presence o oxygen"

• The mechanisms required certain en4ymessuch as superoxide dismutase and catalase"

#" ;uperoxide is convert to hydrogen peroxide

by en4ymes superoxide dismutase"


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+' Hydrogen peroxide is then converted toharmless !ater and oxygen by en4ymecatalase"

& Obligate anaerobes lac1 one or both o theseen4ymes"

&eg: Neocallimastix has superoxide dismutasebut not catalase so its inability to deal !ithH+O+ probably or its ailure to tolerate the

presence o oxygen"

+H+O+ +H+O DO+

catalase


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◦ Fungi need !ater or upta1e o nutrientand metabolic reactions"

◦ Water unavailability I lo! gro!th:

High extracellular osmotic pressuresremove !ater rom cells" This inhibitscell gro!th"

High solute solutions tend to inhibit

gro!th by most microorganisms capableo gro!ing at the typically lo! soluteconcentrations o most environments"


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◦

Organisms adapted to gro!th atrelatively high and very high saltconcentrations2 !hich are reerred to asacultative and extreme halophiles

◦ Fungi more resistant: -olds and yeasts tend to be much more

resistant to high or lo! osmoticpressures than are bacteria"

-olds2 but not bacteria2 tend to be thespoilers o ruits and grains"


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• Typically2 ungi are respond to lo! external!ater potentials by generate an even lo!erinternal osmotic potential2 so that the cell

remain turgid"• ;ometimes2 this is achieved by selective

upta1e and accumulation o JD by marineungi"

• Ho!ever2 high ionic level are potentiallydamaging to the cells"

• -arine ungi seem to ta1e up JD ions

primarily to prevent the more @aD ions romentering the cell"


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• *ommon method o balancing a high externalosmotic environment are:&

#" >ccumulation o sugars and sugar derivatives

that do not interere !ith cellular metabolicpath!ay"

• This osmotically active compound are termedcompatible solutes"

• 5g glycerol %compatible solute' in highlyxerophilic %drought&loving' yeast and3lamentous ungi"


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• !ater stress&tolerant and !ater stress&intolerant ungi

&


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• *ompatible solute in ungal spores

&spore !ith high solute content can germinateaster&lo!er humidity

%spore need to sustain high humidity togerminate'

& compatible solutes derived rom nutrient

storage reserved or rom nutrient ta1en up bythe cells

&eg #eauveria bassiana and Metarhi$iumanisopliae % insect&pathogenic ungi'


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+" *ommonly gro! as saprotroph on thesuraces o living or senescing plants leaves&termed phyllosphere

• 5g: Cladosporium, Alternaria, !ydo&ia,etc

&the presence o dar1 pigmented %melani4ed'hyphae and spores&ability to !ithstandperiodic !etting and drying

• $hyllosphere ungi are naturally and speciallyadapted to the 9uctuating moisture conditionin their habitat %1itchen K bathroom !alls'


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The response o the ungi to duration oexposure to light varies !ith the variationin the light intensity"

Light in the near&ultraviolet %@M' andvisible parts o spectrum %rom about /=,&A+, nm'has relatively little efect onvegetative gro!th o ungi"


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Light also act as trigger or the productiono asexual sporing structures or sexualreproductive structures in several ungi"e"g2toadstool and many


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'enetic dissection o blue light perception inNeurospora crassa

• N crassa being an important model

eu1aryotes• Bt have relatively small genome %about .,

megabases' 2 rapid gro!th andmanipulability2 ease o genetic manipulationby random and stable integration o oreign@> and an abundance o !ell&characteri4edmutants"


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• Bt also preerred model organism orinvestigating light perception because :

i" Bt perceives light only in bluePM range %involved e! genes in this response'

ii" Bt sho!s a pronounced Circadian rhythm&

a molecular cloc1 that has innate periodlength close to +. hours %can be reset byenvironmental light cues'


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• There is a strong interaction bet!een thecircadian cloc1 o Neurospora and theperception o light and subsequent

transduction path!ay"• The remar1able eature o blue&light response

in Ncrassa is that it involves only + proteincomponents and very short signalingcascade"

• There seem to be a dual light&perceptionsystem:


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• There seem to be a dual light&perceptionsystem:

i" Bnvolves W*PW*&+ proteins

ii" Bnvolves MBMB protein•


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#" W*PW*&+& Bnvolves the ungal blue light photoreceptor&

regulatory protein termed White *ollar #%W*&

#'& W* protein interact !ith @> to initiate

gene transcription&

>nother protein %W*&+' act as transcriptionactor and orm complex !ith W*& This W*PW*&+ complex is locali4ed in

nucleus and targets the light signal to the

promoter o the blue light&regulated genes"

W* # d W* + ild i bl


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&W* and W*&+ are !ildtype proteins unableto induced carotenoid synthesis in responseto blue light"

&this system is responsible or dar1&to&lighttransition"

+ MBMB i %+ bl li h h '


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+" MBMB protein %+nd blue light&photoreceptor'

&involved another mutant gene2termed vividthat causes a sustained expression o

carotenoid genes in light" &this MBMB protein is located at the cytoplasm

rather than the nucleus and bind to 9avin&type chromophore"

&it responses to diferent light intensities andmodulating the circadian cloc1"

&the MBMB protein enables Neurospora to

detect changes in light intensity and regulatethe production o carotenoid againstphotodamage"


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TH>@J; FO6 QO6

>TT5@TBO@

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11thenvironmental Factors of Fungal Growth

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