lecture 24 microbial ecology

8/17/2019 Lecture 24 Microbial Ecology

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What is Microbial Ecology?

What is “Microbial”?

What is “Ecology”?

– the study of the interactions between organisms

and their environment

– of or referring to a minute life form; a

microorganism, especially a bacterium that

causes disease !ot in technical use

Microbial ecology " #he study of interactions between

microorganisms and their environment $chemical, physical, and

biological environment%&


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More terms

' (ommunity) an area where organisms can

interact with each other and the nonliving

environment; often called an ecosystem

' Ecological niche) the role an organism

plays within a particular ecosystem

' Microenvironments) small environments

within a larger ecosystem relevant to

microbes


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!utrient a*uistion

' +rimary producers) autotrophs produce which convert(- into organic materials $these includephotoautotrophs and chemilithotrophs.o/idi0e inorganicchemicals for E&; serve as food for consumers anddecomposers

' (onsumer1heterotrophs) utili0e organic cmpds and relyon primary producers; food chain involves primaryconsumers $herbivores& secondary consumers$carnivores that eat herbivores& and tertiary consumers$carnivores that eat other carnivores

' 2ecomposers) digest the remains of primary producersand all consumers; bacteria and fungi are involved in theprocess of minerili0ation $the complete brea3down oforganic molecules into inorganic molecules&


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4iving styles of Microorganisms


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#he term “microbial ecology” really wasn5t incommon

use until the late 6789s

' Why?

Microbial ecology has its roots in microbiology,rather than ecology

The history of the field is largely a transitionfrom laboratory pure cultures to studying

organisms in nature…


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Microbial communities1 Microbial

mat

' #hic3, dense, highlyorgani0ed structureof distinct layers

' :reen $top layercyanobacteria&

' +in3 layer $sulfurbacteria&

' lac3 layer on the

bottom $sulfatereducers


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!utrient (ycling) (!= and +' 2efinition) (Element Cycling, Nutrient Cycling)> the physical movement and chemical transformation ofmaterial by biochemical activities throughout theatmosphere, hydrosphere, and lithosphere(,


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' !utrient cycles and energy flow are

related

'( cycling is most directly related to energyflow

' (- C


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@ood (hain Energetics Dautotrophs) (-→org (

higher plants $


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Elemental (ycling) definitions

' Dssimilatory processes) builds biomass constituents

' 2issimilatory process) reduction coupled to nrg>yieldingo/idation

' Minerali0ation) (onversion from organic to inorganicstate

' /idation) loss of electrons; releases energy

' Beduction) gain of electrons; re*uires energy input

' Bedo/ couple) coupling of o/idation and reduction #he

net difference in the o/idation and reduction half>reactions provides energy for cell function


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The Carbon Cycle

1. ‘Fast’ Cycle – decades or less

a. reservoirs: atmosphere, surface oceans, biota, soils

b. transfers: photosynthesis, respiration, fossil fuel burning

c. Biological processes dominate

2. ‘lo!’ Cycle – millenia

a. reservoirs: deep oceans, sediments, fossil fuels

b. transfers: sediment burial, volcanoes

c. "eological processes dominate


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#he (arbon (ycle1 main types of

processes)

' 6& dissolution and precipitation

' -& physical>chemical e/change of carbon

between environmental compartments

' F& assimilation and dissimilation

Gphotosynthesis, respiration, trophic

transferH

' & conversions between methane and (-


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and bacteria


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!itrogen has numerous o/idation states and is involved

in comple/ chemical pathways, some manners of microbial

energy production, and the cycling of other elements


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Iey nitrogen conversions

' !itrogen fi/ation > (onversion of dinitrogen gas to ammonium' !itrification > (onversion of ammonium to nitrate > aerobic bacteria; different

species responsible for - specific steps in the process' 2issimilatory nitrate reduction – Anaerobic conversion of nitrate to nitrite;

bacteria !itrate used as electron acceptor to drive energy production @irststep in denitrification

' 2enitrification > Multistep reduction of nitrate to gaseous dinitrogen+erformed by nitrate reductase en0yme system > different bacteria mayperform different steps !umerous intermediates !itrate used as electronacceptor to drive energy production

' !itrogen incorporation > Jpta3e of nitrate or ammonium and incorporationinto protein and other cellular constituents +lants, animals and

microorganisms > different organisms prefer nitrate or ammonium Jse ofnitrate is called assimilatory nitrate reduction

' Minerali0ation 1 Dmmonification > Belease of ammonium from organicnitrogen or nitrate > performed by fungi, bacteria


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Dmmonification – the conversion of organic nitrogen $proteins,

amino sugars, nucleic acids, chitin& to ammonium $!<

C&

heterotrophic bacteria and fungi – Kdecomposers5generic e*uation)


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Nitrification – the o/idation of ammonia $!<F& to

nitrite $!-

>& and nitrate $!F

>&

#wo steps, two organisms $autotrophic& !<

F o/idi0ers " !itroso> $Nitrosomonas, Nitrosolobus,

Nitrosospira&

!-

> o/idi0ers " !itro – $Nitrobacter , Nitrospira, Nitrospina

Nitrococcus&+hylogenetically, fairly narrow group of bacteria


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Denitrification – the reduction of nitrate to dinitrogen gas

and nitrous o/ide

Dnaerobic process – !F

> is used as terminal electron

acceptorMany denitrifiers are facultative anaerobes – aerobes that

are capable of anaerobic metabolism when - is

unavailable

Nit ifi ti E t Si ifi


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Nitrification, Ecosystem Significance:

converts relatively immobile form $!<F1!<

C& to very mobile

form $!F

>&; provides substrate for denitrification

:lobal1Begional =ignificance) !itrification is lea3y,

producing both !- $a maAor greenhouse gas – 679 times

more potent than (-& and ! $contributes to acid rain&

Dentirification Ecosystem significance

converts available !F> to inert gases – unavailable forplant upta3e (an form basis for !F> bioremediation

:lobal significance) maAor source of !- $potent

greenhouse gas&


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Environmental aspects of

nitrogen cycle' !itrogen fertili0er application, livestoc3 farm

drainage, and human sewage system lea3age

contribute to nitrate contamination of surface

and waters $blue baby syndrome&' !/ gas formation contributes to greenhouse

effect

' 2enitrification 1 ammonium volatili0ation can

deplete agricultural fields of natural nitrogen

stores


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Plant: microbe symbiosis

N2 fixation


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The Sulfur Cycle

' = is the 69th most abundant element in theEarth5s crust

' = ma3es up about 6L of microbial biomass dry

weight' = is re*uired for amino acid synthesis, vitamins,

hormones, coen0ymes, connective tissues, plantlipids,

' = is not usually a limiting nutrient' = is intensively cycled through the biosphere

' =ome important similarities to ! cycle


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Why is = so intensely cycled)

=ulfur has a wide range of o/idation states)

=-> inorganic sulfides, organic mercaptans

=9 elemental sulfur

=-F-> thiosulfate

=E-> sulfate

arious forms of = have o/idation states that vary by a total of N

electrons

$+ is not vigorously cycled; it does not have many differentbiologically relevant o/idation states&


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+hosphorous cycling

' iologically important nutrient

' (ycle is largely geochemically driven

' @ew o/idation states' Most + in the form of organic or inorganic

phosphate


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a!or contributor to global N2

fixation

' En0yme " nitrogenase

' nly bacteria produce nitrogenase

' !itrogenase is e/tremely o/ygen sensitive' MaAor !- fi/ers $symbiotic and free>living&

are aerobic $(yanobacteria, Bhi0obium,

radyrhi0obium&


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Symbiotic interactions bet"een

#lants an$ microorganisms

' (onsistent theme of root e/udate

importance

' (ontinuum between mutualism andparasitism

' E/tensive coevolutionary history

' (ritical importance for nutrient cycling, soilfertility and human economy

hi & $' t h i


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ycorrhi%ae &re$' on root hairs

&yello" an$ green'' Mycorrhi0ae are fungi

growing in symbioticrelationships with plantroots

' #hey help plants ta3eup phosphorous, whilethey gain nutrientsthrough rot secretions

' ONPL of vascularplants havemycorrhi0ae


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' 4egume plants secrete specific flavonoids, which are detected by

interaction with bacterial !od2 proteins When !od2 binds a

flavonoid it activates other nodulation genes =ome of the nod

genes code for en0ymes that ma3e !od factors, which are

recogni0ed by the plant #here are many different flavonoids and

!od factors and lots of variety in the host specificity between

plants and !hi"obia' the bacteria to move to the root #he bacteria enter the outer root

tissue and produce cyto3inins $plant hormones& which cause

division of plant cells to form nodules #he bacteria lose their

outer membranes and become irregular in shape > RbacteroidsR

!hi"obium continued


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(oot no$ule of #lants by

bacterial (hi%oium s#ecies


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Microorganisms and ruminants

' Dnother mutualistic relationship e/ists betweenmicroorganisms and the various herbivorescalled ruminants

' bacteria live in their rumen which proceeds theirtrue stomach facilitating brea3down of cellulose$the most abundant (>sources of food that mostanimals can not digest&

' Each m4 of rumen contains 6969

bacteria flora' #he plethora of gas produced is released when

the animal belches

( t t d i i bi l l


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(urrent trends in microbial ecology)

' space e/ploration – microbes in e/treme environments

$hot springs, thermal vents, lithosphere&

' (limatic change interactions with microbial

communities' molecular techni*ues – diversity of microorganisms

new methods to assess presence1abundanceof individual species in situ

' We can now culture S6L of all environmentalpro3aryotes

' 2oes microbial diversity matter?

' What roles do any specific cells play in a community?

lecture 24 microbial ecology

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