unit 5 microbial growth part a

7/28/2019 Unit 5 Microbial Growth Part A

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GENERAL MICROBIOLOGY GENERAL MICROBIOLOGY

Microbial Growth


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How do bacteria grow?

Since microorganisms are so small itis usually inconvenient to studyindividual cell.

follow changes in the total

population . Microbial growth involves an

increase in the number of cells.


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Growth of most microorganismsoccurs by the process of binaryfission (Asexual Reproduction).

MICROBIAL GROWTHMICROBIAL GROWTH

This means that the parent cellproduces exact copies of itself


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(Two cells arise from one)

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The required time for growth cycle is

highly variable and is dependent on cell


ype an grow con ons

eg. E. coli has a generation time of 17 min

under optimal conditionsMost bacteria slower than 20 minBacteria tends to grow faster than

yeast and mould.


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BINARY FISSIONBINARY FISSION


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Doubling time or generation timerefers to the period required for cells in amicrobial population to grow divide and

produce two cells for each one that

MICROBIAL GROWTH TERMSMICROBIAL GROWTH TERMS

.

Doubling time remains constant in a

given population until nutrients becomedepleted or toxic metabolic wasteaccumulate.


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MICROBIAL GROWTH TERMSMICROBIAL GROWTH TERMS

Growth Rate :change in cell number/cellpopulation (or mass) per unit time Growth rate is the doublin time

per hour

Generation Time :interval for one cell to become two(or doubling time)


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Microorganisms show acharacteristic growthpattern when inoculated


medium in a closed

system.


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There is usually a lag phase , thenexponential growth commences. As essential nutrients are depleted or

toxic products build up, growth


,the stationary phase . If incubation

continues, cells may begin to die (thedeath phase ).


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Phases of Growth

Immediately after inoculation of thecells into fresh medium, thepopulation remains temporarily

unchanged.

LAG PHASELAG PHASE

Adjustment period for organism toadopt to new surroundings. Repairany damage in cell and re-synthesisof essential cell constituents.


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Occurs when: old cells transferred to freshmedium

cells transferred from rich medium

LAG PHASELAG PHASE

Absent when: exponentially growing cellstransferred to fresh portion of

same media


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Phases of Growth

Although there is no apparent celldivision occurring, the cells maybe growing in volume or

LAG PHASELAG PHASE

proteins, RNA , etc., and

increasing in metabolic activity.


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Phases of Growth

The length of the lag phase isapparently dependent on a widevariety of factors including:

LAG PHASELAG PHASE

2.time necessary to recoverfrom physical damage orshock in the transfer ;


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Phases of Growth

3. time required for synthesis of essential coenzymes or divisionfactors;

LAG PHASELAG PHASE

. me requ re or syn es s onew (inducible) enzymes that

are necessary to metabolize thesubstrates present in the medium.


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Exponential (log) Phase :

The exponential phase of growth is apattern of balanced growth wherein all

the cells are dividing regularly by binary

LAG PHASELAG PHASE

,progression.

The cells divide at a constant ratedepending upon the composition of thegrowth medium and the conditions of

incubation.


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Exponential (log) Phase :

The exponential phase of growthis a pattern of balanced growth

LAG PHASELAG PHASE

regularly by binary fission, and

are growing by geometricprogression.


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The cells divide at a constantrate depending upon thecomposition of the growth

medium and the conditions of

EXPONENTIAL (LOG) PHASEEXPONENTIAL (LOG) PHASE

incubation.


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Exponential growth cannot occur indefinitelyOne (1) bacterium

weight one trillionth of a gram (1/1000000000000)

with a generation time of 20 minutes

EXPONENTIAL GROWTHEXPONENTIAL GROWTH

Growing exponentiallywould produce apopulation that weighted4,000 times that of theearth in 48 hours.


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Exponential growth cannot be continuedforever in a batch culture (e.g. a closedsystem such as a test tube or flask.Population growth becomes limited byone of three factors:

STATIONARY PHASESTATIONARY PHASE

1. Exhaustion of available nutrients ;2. Accumulation of inhibitory

metabolites or end products ;3. Exhaustion of space , in this case called

a lack of "biological space".


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The stationary phase, like the lagphase, is not necessarily a period of quiescence.

During the stationary phase there is


while others grow).


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Bacteria that produce secondarymetabolites , such as antibiotics, doso during the stationary phase of thegrowth cycle


metabolites produced after the activestage of growth.

Endospore producing organismsproduced endospores


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If incubation continues afterthe population reachesstationary phase, a death

hase follows in which the

DEATH PHASEDEATH PHASE

viable cell population declines.


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(Note, if counting by turbidimetricmeasurements or microscopic counts, thedeath phase cannot be observed.).

During the death phase, the number of viable cells decreases geometrically

DEATH PHASEDEATH PHASE

exponen a y , essen a y e reverse ogrowth during the log phase.


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BACTERIAL METABOLISM


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Carbon metabolism in bacteria iseither: Heterotrophic: organic carbon

compounds are used as carbon


sources. All animals, most bacteria and

fungi are heterotrophic. Heterotrophic bacteria include

parasitic types.


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Autotrophic: cellular carbon isobtained by fixing carbondioxide.

E . hototro hic c anobacteria


green sulfur-bacteria and somepurple bacteria, but also manychemolithotrophic species, such asnitrifying or sulfur-oxidisingbacteria.


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MICROBIAL METABOLISMMICROBIAL METABOLISM

Chemo organotrophsobtain their energy from theoxidation of organiccompounds

All cells need carbon and energy sources

obtain their energy from theoxidation of inorganiccompounds

Photoautotrophscontain pigments thatallow them to use lightas an energy source


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Energy metabolism of bacteria is eitherbased on:

Phototrophy : use of light throughphotosynthesis, or


Chemotrophy: use of chemical

substances for energy, The chemical substances are mostly

oxidised at the expense of oxygen or

alternative electron


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Chemotropes are further subdivided:

Lithotrophs: use inorganic electrondonors (eg. hydrogen, carbon monoxide,ammonia, ferrous iron and otherreduced metal ions, and several reduced


su ur compoun s.

Organotrophs: use organic compounds

as electron donors. Most lithotrophic organisms are

autotrophic, whereas organotrophic

organisms are heterotrophic.


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Chemotrophic organisms use therespective electron donors for:

energy conservation (byaerobic/anaerobic respiration or


biosynthetic reactions (e.g. carbondioxide fixation),

Phototrophic organisms use theirelectron donors only for biosynthetic

purposes


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Aerobic organisms use oxygen asthe electron acceptor in the electrontransport chain.


inorganic compounds such asnitrate, sulfate or carbon dioxide aselectron acceptors in the electrontransport chain.


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In both aerobic phototrophyand chemolithotrophy,oxygen is used as a terminal


anaerobic conditionsinorganic compounds areused instead .


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In the absence of possible electronacceptors chemotrophs carry outfermentation , where the electrons

taken from the reduced substrates


are rans erre o ox seintermediates to generate reduced

fermentation products (e.g. lactate,ethanol, hydrogen, butyric acid). These organisms do not utilize the

electron trans ort chain.


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Facultative anaerobes canswitch between fermentation anddifferent terminal electron

acceptors depending on the


environmental conditions inwhich they find themselves.


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Combining their nutritionalpatterns, all organisms in naturecan be placed into one of four

se arate rou s:


1. photoautotrophs,

2. photoheterotrophs ,3. chemoautotrophs, and4. chemoheterotrophs .


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Nutritional TypeNutritional Type EnergyEnergy

SourceSource

CarbonCarbon

SourceSourceExamplesExamples

Photoautotrophs Light CO2

Cyanobacteria,some Purple andGreen Bacteria


Photoheterotrophs Lightcompounds

Green Bacteria

Chemoautotrophs orLithotrophs(Lithoautotrophs)

Inorganic

compounds,e.g. H 2, NH3,NO2, H2S

CO2

A few Bacteriaand many

Archaea

Chemoheterotrophsor Heterotrophs

Organiccompounds

Organiccompounds

Most Bacteria,some Archaea


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1. Photoautotrophs use light as anenergy source and carbon dioxide astheir main carbon source.Photoautotrophs transform carbon


and oxygen goes throughphotosynthesis .

They include photosynthetic bacteria (greensulfur bacteria, purple sulfur bacteria, andcyanobacteria), algae, and green plants.


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2. Photoheterotrophs use light as anenergy source but cannot convertcarbon dioxide into energy. Insteadthey use organic compounds as acarbon source.


They include the green nonsulfur

bacteria and the purple nonsulfurbacteria.


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3.Chemolithoautotrophs useinorganic compounds such ashydrogen sulfide, sulfur, ammonia,nitrites, hydrogen gas, or iron as anener source and carbon dioxide as


their main carbon source.

They include sulphur bacteria, the ironbacteria, the nitrifying bacteria, thehydrogen bacteria, and the methanebacteria .


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MEDIA TYPESDefined Media/Synthetic media

A defined medium is one in which the exactchemical composition is known .

A defined medium that just has enough ingredients tosupport growth is called a minimal medium .

The number of ingredients in a minimal medium varies depending on the microorganism.

E. coli for instance needs only a simple minimalmedium. Minimal medium can only be prepare formicroorganisms with known nutritionalrequirements .

For example Glucose Salt Agar (GSA)


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Minimal medium typically contains: a carbon source for bacterial growth, which

may be a sugar such as glucose, or a lessenergy-rich source like succinate

MEDIA TYPES

var ous sa s, w c may vary amongbacteria species and growing conditions;these generally provide essential elementssuch as magnesium, nitrogen, phosphorus,and sulfur to allow the bacteria tosynthesize protein and nucleic acid


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Complex Media

A complex medium is one in which the exact chemicalcomposition is not known. It is made from extracts of naturalmaterials like beef, blood, casein, yeast and soybeans.

Contain all the elements that most bacteria need forgrowth and are non-selective , so they are used for the

MEDIA TYPES

general cultivation and maintenance of bacteria kept inlaboratory culture collections.

The most common complex media used is nutrient agar.

Complex media are easy to prepare and can support the growth of most microorganisms.

Eg. Glucose Yeast Peptone Agar, Nutrient Agar, Plate Count Agar


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Hektoen enteric agar (HE)

which is selective for Gram-negative bacteria

Mannitol salt agar (MSA)

which is selective for Gram-

MEDIA TYPES

for mannitol usage

Terrific Broth (TB) is usedwith glycerol in cultivatingrecombinant strains of Escherichia coli.

Mannitol Salt Agar (MSA) selects for Staphy lococcus


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Selective Differential Media

Allow growth of only the desired microbes andalso distinguish among selected organismsaccording to the appearance of isolated colonies Eosin Methylene Blue (EMB) is selective for Gram-negative

bacteria and differential for lactose fermentation

-

MEDIA TYPES

and differential for lactose fermentation

MacConkey Agar differentiatelactose fermenting andnonfermenting

Eosin-methylene blue (EMB)selective for gram-negativebacteria and differentiate betweenthe colonies of lactose fermenting

and nonfermenting.


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Enrichment Culture An enrichment culture is used to encourage

the growth of a particular microorganism,usually in low concentration, from a mixed

culture.

MEDIA TYPES

Isolation of nitrogen-fixing bacteria using medialacking nitrates

Isolation of halophiles using high salt concentration

Isolation of thermophiles using high temperatures


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NUTRITIONAL REQUIREMENTS

Nitrogen Needed for Protein and nucleic acid synthesis .

Obtained from decomposition of proteins or fromNH 4 + or NH 3 ; a few bacteria are capable of nitrogen (N

2) fixation .

Sulfur Needed to synthesize sulfur-containing amino

acids and certain vitamins . Depending on the organism, sulfates, hydrogen

sulfide, or sulfur-containing amino acids may beused as a sulfur source.


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Phosphorus Needed to synthesize phospholipids, DNA, RNA,

and ATP . Phosphate ions are the primary source


race e emen s Trace elements are elements required in very

minute amounts , like potassium, magnesium,

calcium, and iron They usually function ascofactors in enzyme reactions.

Cofactors usually function as electron donors or electronacceptors during enzyme reactions.


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Growth factors Growth factors are organic compounds

such as amino acids, purines,pyrimidines, and vitamins that a cell


synthesize itself .

Organisms having complex nutritionalrequirements and needing many growthfactors are said to be FASTIDIOUS .

unit 5 microbial growth part a

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