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Exam 1 is Tuesday Sept 15th 40 MC questions Same room and time as lecture You must have student ID and pencils Do not bring a scantron

Office hours from now until exam: Tues Sept 8th 10:30-11:30 Wed Sept 9th 8:00-9:00 and 1:30-2:30 Thurs Sept 10th 8:00-9:00 and 10:30-11:30 Mon Sept 14th 8:00-9:00 and 1:30-2:30 Tues Sept 15th 8:00-9:00

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Bacterial Cell SurfaceStructures

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Pili & Fimbriae Bacteria may have 1, both, or neither

Fimbriae: Non-motile extensions that help bacteria attach tosurfaces and to other bacteria (Neisseria, biofilms)

Shorter than flagella, may have 100s per cell

Pili: aka- conjugation pili

Hollow, non-motile tubes made of protein called pilin

that connect some cells. Longer than fimbriae, shorter than flagella; mayhave 1-10 per cell

Used to move DNA from 1 cell to another by

conjugation

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E. coli

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capsule/slime layer/glycocalyx

Sticky polysaccharideor polypepetide layersurrounding cell

Protects cell from:phagocytosis

desiccation Help cells attach to

objects such as teeth

S. mutans

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S. pneumoniae

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Cell Motility

Flagella Long, helical protein filaments

Attached at ends, or over whole cell

- Flagella rotate to propel cellProton passage drives

rotation

- Clockwise orcounterclockwise

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Bacterial flagella rotate;Eukaryotic flagella- whip-like motion

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http://video.google.com/videopl

http://video.google.com/videoplay?docid=5599433730120943955&q=motile+bacteria&total=8&start=0&num=10&so=0&type=search&plindex=1http://video.google.com/videoplay?docid=5599433730120943955&q=motile+bacteria&total=8&start=0&num=10&so=0&type=search&plindex=1

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Arrangement of Flagella

Monotrichous- single flagellum at 1 end

Lophotrichous- several flagella at 1 or bothends

Peritrichous- several flagella all around cell

Amphitrichous- 1 on each end

peritrichousmonotrichous

lophotrichous

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monotrichouslophotrichous

amphitrichous

peritrichous

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Structure of the flagella

3 parts:1. Basal body

2. Hook3. Filament

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Gram-negative Bacterium Gram-positive Bacterium

cytoplasmicmembrane

peptidoglycan

outermembrane

L ring

P ring

MS ring

C ring

MS ring

C ring

Basal Body Imbedded within cell envelope

Made of 2 or 4 protein rings connected by acentral rod C ring- in G+ & G- MS ring- in G+ & G- P ring- in G- only L ring- in G- only

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C ring- In cytoplasm. Attached to innersurface of cytoplasmic membrane

MS ring- In cytoplasmic membrane. Endof central rod is attached to MS ring.

P ring- In peptidoglycan layer

L ring- In LPS layer

Gram-negative Bacterium Gram-positive Bacterium

cytoplasmicmembrane

peptidoglycan

outermembrane

L ring

P ring

MS ring

C ring

MS ring

C ring

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k

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Hook

Curved structure

made of protein;connects filament tobasal body

Filament

Long, rigid, helical

structures made ofprotein called flagellin

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Prokaryotes such as filamentouscyanobacteria, Myxococcus, Cytophaga&

Flavobacteriummove by gliding motilityinstead of flagella.

Gliding can occur from slime secretion that

moves cell along solid surface.

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cyanobacterium Oscillatoria

Flavobacterium

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Motile bacteria can respond to chemical &

physical gradients in environment by moving

toward or away from the signal molecule.

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Directed movements toward or away from achemical or physical signal are known as

taxes.Chemotaxis directed movement oforganisms in response to chemical signals.

Phototaxis directed movement oforganisms in response to light.

Aerotaxis directed movement of organisms

in response to oxygen.Osmotaxis - directed movement oforganisms in response to ionic strength.

D t ti f h t i

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Attractant

Neither attractant nor repellent Repellent

Initial insertion of capillary

Demonstration of chemotaxis

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Phototrophic bacterium Rhodospirillummoving toward light

0 hr

2 hr

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Attractants cause counterclockwiserotation

Flagella bundle together Push cell forward

Run

Repellents cause clockwise rotation Flagella fly apart

Tumble = change of direction

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Runs + tumbles cause random walkReceptors detect attractant

concentrations Sugars, amino acids

Attractant concentration increasesand prolongs run Net movement of bacteria towardattractants

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Chapter 4Bacterial Culture, Growth, andDevelopment

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Microbial Nutrition All life requires:

Electron flow, to drive all life processes Drives ions into, out of cells

Used to create ATP

Energy, to moveelectrons

Materials, tomake cellparts

Nutrients- CHONPS

Electron flow requires:

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Electron flow requires: Source of electrons

Lithotrophs-Inorganic molecules are electron donors

(iron) Organotrophs-

Organic molecules are electron donors(glucose)

Ultimate electron acceptor

Inorganic molecules (nitrate or oxygen)Respiration

Organic molecules (pyruvate)

Fermentation

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Source of energy

Phototrophs Light energy excites electrons Excited molecules are electron donors

Chemotrophs Chemicals are electron donors Oxidation of chemical

Oxidation = donation of electrons

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Nutrients

Macronutrients

Major elements in cell macromolecules

C, H, O, N, P, S

Ions necessary for protein functionMg2+, Ca2+, Fe2+, K+

Micronutrients

trace elements (Co, Cu, Zn, etc) growth factors (organic compounds)necessary for enzyme function

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Carbon- large amount needed by cells toform organic compounds (amino acids,fatty acids, sugars, & nitrogenase bases)to carry out cellular functions.

Autotrophs- prokaryotes that can make

all cellular structures from CO2.

Heterotrophs- must obtain carbon fromorganic compounds. (most prokaryotes)

Nitrogen needed by cells for amino acids

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Nitrogen- needed by cells for amino acids,nitrogen bases, & several other cellconstituents.

Nitrogen-fixing prokaryotes- capable ofusing atmospheric nitrogen gas.

Most prokaryotes obtain nitrogen fromcompounds such as ammonia & nitrate.

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Energy sources:Chemoorganotrophs

-energy from oxidation(removing electrons) oforganic compounds

Chemolithotrophs

energy from oxidationof inorganic compounds.Only in prokaryotes.Advantage?

Phototrophs - containpigments that allowthem to use light as anenergy source.

Advantage?

Carbon sources:Heterotrophs - carbon

source is organic carboncompounds

Autotrophs - carbonsource is carbon dioxide

These terms can becombined to morecompletely describe anorganism.

Example-photoautotroph obtainsenergy from light &carbon from carbon

dioxide.

N t i t U t k

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Nutrient Uptake Passive diffusion

Some substances pass freelythrough membranes O2, CO2

Follows gradient of material Facilitated diffusion Transporters pass material

into/out of cell Follows gradient of material

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Nutrient UptakeActive Transport

ABC Transporters Use ATP energy to pass

material into cell

Transport material againstgradient

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Symport and Antiport

Gradient of one molecule transportsanother

Transports material against its gradient

Symport: Gradient

of pumps in

same direction

Antiport: Gradient

of pumps in

opposite direction

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Phosphotransferase

System (PTS)Uses ATP energy to pass

material into cell

glucose enters cell and is phosphorylated. As

a result, gradient of pushes more glucose

inside.

(glucose-6-phosphate) cannot pass out of cell.

Nutrient Upt ke Active Tr nsp rt

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Phosphotransferase

System (PTS)Uses ATP energy to pass

material into cell

Modifies material as itenters cell

glucose enters cell and is phosphorylated. As

a result, gradient of pushes more glucose

inside.

(glucose-6-phosphate) cannot pass out of cell.

Nutrient UptakeActive Transport

Culturing Bacteria

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Culturing Bacteria Culture media-all materials necessary for

growth Varies for different bacterial species

Electron source

Energy source If not phototrophic

Carbon source

If not autotrophic Nitrogen source

If not N2

-fixer

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Obtaining Pure Cultures

Dilution streaking

Streak cells on plate

All cells in colony derivefrom single cell

Genetically identical

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Dilution in liquid culture

Reduces number ofcells in each tube

Spread liquid on plate

to see single colonies

Counting Bacteria

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Counting BacteriaTotal Counts/Direct counts

Petroff-Hauser counting chamber viewed under microscope & cells in grids

are counted

Counts cells directly

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Can be done electronically using CoulterCounter

Cant tell if cells are alive or dead Can use special stains to distinguish living

cells

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Spectrophotometer/Turbidity measurements

Measures optical density

indirect but rapid a suspension of cells looks turbid

(cloudy); cells scatter light passing

through suspension more cells, more turbid, more light is scattered

cant tell if cells are alive or dead

light

bulbPhotodetector

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For turbidity measurements to besubstituted for direct counting methods a

standard curve must be made. Once a standard curve is made for a specific

organism growing in a specific culture

medium, it can be used for future cultures ofthe same organism in the same medium toestimate cell numbers.

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Viable counts

In many cases, you dont want to count dead

cells, so viable count methods let you countonly live cells.

Counts only cells able to reproduce

Form colonies Requires time to form colonies

(overnight)

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C i f b i i l i

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Concentration of bacteria in a sample isunknown.

Before spread plates or pour plates are done,dilution of sample is necessary.

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Why study microbial growth?

to understand science of microbial growth practical situations which call for control of

microbial growth:

Food industry, health care industry, etc

Wh 1 ll di id t f 2 ll

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When 1 cell divides to form 2 cells, onegeneration has occurred.

Generation time- time for # of cells in aculture to double.

Many bacteria have generation time of 1-3

hours. Some as little as 10 minutes, somecan be days.

Generation time is affected by nutritional &

genetic factors. Under ideal conditions, one generation in

Escherichia colitakes 20 minutes.

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Also called doubling time because witheach generation the cell population doubles

Generation time in lab is usually shorterthan in nature. Why?

constant ideal conditions for labcultures; natural populations rarely haveideal conditions

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http://video.google.com/videoplay?do

exponential growth-

http://video.google.com/videoplay?docid=-9201923798446864025&q=bacteria+growth&total=148&start=0&num=10&so=0&type=search&plindex=0http://video.google.com/videoplay?docid=-9201923798446864025&q=bacteria+growth&total=148&start=0&num=10&so=0&type=search&plindex=0

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p gcharacteristic type of growthpattern of microbial populations

where the number of cells doublesover a regular time interval

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Graphical determination of generation time

Number of cells/ml is plotted vs time on

semi-log paper Semi-log paper- linear scale on X-axis &

logarithmic scale on Y-axis

Generation time is found by determining thetime it takes the # of cells to double

Each cycle on the Y-axis

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yrepresents a power of 10Example:

bottom 1 might represent 106cells/ml, then next 1 wouldrepresent 107

Or bottom 1 might represent0.001 and next 1 wouldrepresent 0.01Depends on the data you

haveImportant to label the axesCan plot # of cells or opticaldensity/absorbanceturbidit

Use the following

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X-axis- time

Y-axis- # of cells

Use the followingdata to plot

growthcurves andcalculategeneration timegraphically

absorbance Ti

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Cells/ml Time

1.5 x 106 0

1.5 x 106 1

1.5 x 106 2

2.0 x 106 3

4.5 x 106 4

1.3 x 107 5

4.5 x 107 6

2.2 x 108 7

1.0 x 109 8

2.8 x 109 9

4.5 x 109 10

5.5 x 109 11

6.2 x 109 12

7.0 x 109 13

8.0 x 109 14

absorbance Time

.003 0

.003 1

.004 2

.008 3

.014 4

.033 5

.085 6

.180 7

.410 8

1.20 9

3.00 10

5.00 11

8.00 12

9.00 13

9.00 14

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Generation time

is ~ 30 minutes

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The Growth Cycle

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The Growth CyclePopulations of

microorganismsshow a

characteristic

growth patternwhen inoculated

into a fresh

culture medium

Log scale necessary to show wide range of concentrations

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Exponential growth phase

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Exponential growth phase Also called logarithmic (or log) phase

Increase in cells is geometric 1 cell will become 2, then 4, then 8, then 16, etc.

Shortest generation time time it takes for

number of cells in a culture to double

Stationary phase

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Stat onary phase key nutrient will run out or toxic waste

product will build up Most cells survive but stop dividing

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Batch culture vs continuous culture/chemostat

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Batch culture vs continuous culture/chemostat

Batch culture-

Constant volume of culture medium; closedsystem- nothing added or removed; commonlyused in lab

What happens to medium when organisms are

growing in it? How does it change over time? continually altered by metabolic activities of

organisms growing in it; nutrients depleted;

wastes build up

Continuous culture-F h di t tl dd d d di

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Fresh medium constantly added, used mediumconstantly removed, nutrient concentration stays

same

Continuous culture-F h di t tl dd d d di

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Fresh medium constantly added, used mediumconstantly removed, nutrient concentration stays

sameChemostat- continuous culture device; allows cellpopulations to remain in exponential growth for longperiods

In last column of namefield on back of scantron

Last, First blank

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field on back of scantron,bubble in your sectionnumber.

Leave the next to lastcolumn in name fieldblank.

Section Lab time Letter to

bubble in

1 7:40 A

2 9:10 B

3 10:40 C

4 12:10 D

5 1:40 E

6 3:00 F

7 4:30 G

Do not touch

LSU ID#

lab section

ll ff

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Cell Differentiation

Cells respond to changing environment Endospores

Form inside (endo) mother cell

Dormant survival structure formed by some

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Dormant survival structure formed by somespecies of Gram + rod-shaped bacteria

during harsh conditions. Ex. Bacillus& Clostridium

Resistant to heat, radiation, drying, acids,

etc. Can survive indefinitely.

endospore

Vegetative cell

Sporosarcina

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Sporulation- formation

of an endospore whenenviromental conditionsare not favorable.

Germination- formationof a vegetative cellfrom an endosporewhen conditions arefavorable.

sporulation

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vegetative growth

nutrient starvation

sporulation

sporangium

is degraded

free endosporesporangium with

endospore

germination

Endospore intracellular location

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Terminal Subterminal Central

Endospore intracellular location

Endosporeinside cell

Structure of endospores

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p Core- center of endospore. Contains cell wall,

CM, cytoplasm & nucleoid.

Cortex- surrounds core. Made of looselycross-linked peptidoglycan.

Spore coat- protein which covers cortex.

Exosporium- thin layer of protein whichcovers the spore coat

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Calciumdiplicolinic acid helps dehydrateendospore, stabilizes DNA & protects itfrom heat denaturation.

Small acid-soluble proteins protect DNAfrom UV radiation, desiccation, dry heat &

also serve as carbon & energy source duringgermination.

Cell Differentiation

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HeterocystsDifferent cells producedifferent nutrients

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M s s

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MyxosporesForm inside fruiting body

Multicellular structure

Actinomycetes form

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Actinomycetes formspores

Food runs out Produce aerial hyphae

Disseminates cells

Streptomyces

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Chapter 5Environmental Influences and

Control of Microbial Growth

Environmental factors that affect

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Environmental factors that affectmicrobial growth

Temperature

Pressure

Osmolarity pH

Oxygen

Temperature

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p Temperature is a major environmental

factor controlling microbial growth. cardinal temperatures- minimum, optimum,& maximum temperatures for an organism

minimum temperature - cellular processesslow; cytoplasmic membranes stiffen

maximum temperature- proteins start todenature

optimum temperature- organism growsbest; between min & max

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Microorganisms can be grouped by the

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g g p ytemperature ranges they require.

P h hil

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Psychrophiles

Cold: OC20C

Mesophiles

20C45C

Thermophiles40C80C

Extreme thermophiles

65C113C

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Psychrophiles-

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Psychrophiles found in constantly

cold environments

Example:Chlamydomonas-snow algae

pink snow algae

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pink snow algaeChlamydomonas

M l l d t ti f h hil

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Molecular adaptations of psychrophiles:

Membranes have high content ofunsaturated fatty acids - semi-fluid at lowtemperatures

Proteins are more flexible compared tomesophiles or thermophiles

Cryoprotectants can be used to preserve

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Cryoprotectants can be used to preservemicrobial cultures at low temps

10% DMSO (Dimethylsulfoxide) &10% glycerol are commonly used inlaboratories to preserve microbial cultures

for long time in freezers.

Mesophiles- midrange optimum

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Mesophiles midrange optimumtemperature

Found in warm-blooded animals & manyterrestrial & aquatic environments.

Examples- most organisms you are familiar

with such as Escherichia coli(found in thehuman intestine).

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Places thermophiles are found:

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soils subjected to full sunlight

fermenting materials (compost piles) hot springs

Thermus aquaticusis a common hot

spring thermophile. The heat stableDNA polymerase from this bacterium ismass produced and used in laboratories

to replicate DNA in a test tube.

Grand prismatic spring in Yellowstone

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http://video.google.com/videoplay?docid

Molecular adaptations of thermophiles:

http://video.google.com/videoplay?docid=6706395257721771028&ei=PvfXSKXuGoe8rALpt-HcAg&q=black+smoker+vents&vt=lf&hl=enhttp://video.google.com/videoplay?docid=6706395257721771028&ei=PvfXSKXuGoe8rALpt-HcAg&q=black+smoker+vents&vt=lf&hl=en

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Molecular adaptations of thermophiles:

Membranes have a high content of

saturated fatty acids stable &functional at high temperatures

Enzymes are heat stable- proteins are

more rigid compared to mesophiles orpsychrophiles

Heat shock response

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p

Occurs at high end of temperature range

Emergency proteins produced Help keep proteins from denaturing

Induced by many stressful conditions

Heat

High salt concentrations

Arid conditions

Pressure Barophiles

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Barophiles

Adapted to high pressures

Up to 1,000 atm

Barotolerant organisms

Grow at high, but not very highpressure

Barosensitive organisms

Die at high pressure Most typical bacteria, all mammals

Osmolarity

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Osmolarity

Water moves from areas of high waterconcentration to areas of lower water

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concentration to areas of lower waterconcentration.

Water moves from areas of low soluteconcentration to areas of high soluteconcentration.

The diffusion of water is called osmosis.

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In a hypotonic environment the cell wall ofmost prokaryotes prevents too much water

from entering cells even if equilibrium isnever reached.

Isotonic equal amount of solutes/wateron inside & outside of cells

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However, there is no physical barrier thatprevents cell from losing too much water if

cell is in hypertonic environment. Some cells can increase soluteconcentration in cell to prevent too muchwater loss by:

1. pumping inorganic ions (K+) into the cell;

2. making or concentrating an organic

solute (glycerol) in the cell

Osmophile- organism that grows in highsolute concentrations (hypertonic

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solute concentrations (hypertonicenvironments)

Halophiles-grow best in high salt habitats Vibriolives in ocean; % salt in ocean?

Extreme halophiles require high levels (15%

to 30%) of salts for growth. Halobacterium salinarium(requires 25%

salt)lives in very salty lakes

Halotolerant- can survive at higher saltconcentrations but grow best in absence of salt Staphylococcus

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Halobacterium

salinarium

End of exam 1 material!

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The rest of Ch 5 will be covered on exam 2.

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Exam 2 material begins here Chapter 5 continued

pH

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pH- relative hydrogen ion concentration in

a solution Scale is from 0 to 14

7 is neutral, < 7 is acidic, > 7 is basic

Most bacteria grow at pH of 6-8 Bacteria can be found to exist at almost

any pH

Most cells internal pH remains near 7regardless of pH of their environment

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Sulfur oxidizing Bacteria

andArchaea

Iron oxidizing BacteriaAcetic acid Bacteria

Lactic acid Bacteria

Archaea extreme halophiles

cyanobacteria

Human intestinal flora

Most organisms have a pH range at which

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g p gthey can grow of 2-3 pH units.

Acidity or alkalinity of an environment cangreatly affect microbial growth

Weak acids can pass through membranes

Good food preservatives

Classification based on optimal pH

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Some organisms have evolved to grow best at

low or high pH, but most organisms growbest between pH 6 & 8 & are calledneutralophiles (neutrophiles).

A id hil b t t l H

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Acidophiles- grow best at low pH

Stability of CM is critical since increases inpH can cause lysis

Ex. Many fungi, Thiobacillusproduces

sulfuric acid, volcanic thermal soil archaeaPicrophilus oshimaegrows optimally at pH0.7

S lf l b h hili

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Sulfolobus- thermophilic

and acidophilic

Th H S l

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The pH Scale

0 7 14

Most bacteria and protozoa

Most fungi

Alkaliphiles- grow best at high pH found in soda lakes & high carbonate soil

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found in soda lakes & high carbonate soil Many species of Bacilluslive in very alkaline

soils Bacillus firmushas a pH range of 7.5-11. Proteases & lipases made by alkaliphiles are

mass produced & used in householddetergents.

AKA:

Alkalophiles

Alkalinophile,

Basophile

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cyanobacterium Spirulina- alkaliphile

Oxygen

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Microorganisms vary in their need or

tolerance of oxygen (O2) & can begrouped based on their requirements forO2.

oxic environment- O2 is present

anoxic environment- no O2 is present

Aerobes- use O2 to generate energy byrespiration

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respiration

Facultative aerobes use O2 in respirationbut can also grow in anoxic environments.Ex. Streptococcus

mutanson teethE. coliin large intestine

Obligate aerobe- use O2 in respiration &

require oxic environments for growth. Growat atmospheric O2 levels (21%).

Ex. Micrococcus luteus

Microaerophile- use O2 in respiration butl 1 %

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require low O2 concentrations, 2-10%,

(microoxic environments) to grow.Ex. Streptococcus pneumoniae

Anaerobes- cannot use O2 in respiration & maybe inhibited or killed by O

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be inhibited or killed by O2.

Aerotolerant anaerobes- do not use O2 togenerate energy but can survive in presenceof it. Ex. Streptococcus pyogenes

Obligate anaerobes- can only grow in anoxicenvironments; may die if even minute amountof O2 is present.

Ex. Clostridium sporogenes,Bacteroidesinlarge intestine

A reducing agent such as thioglycolate can beadded to a medium to test an organism's

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added to a medium to test an organism srequirement for O2.

Thioglycolate reacts with O2, reducing it towater.

In a culture medium, thioglycolate will convertall O2 to water; only top of

culture is exposed to O2 in the air.

The position of thebacteria withinth thi l l tO

blig

ate

Aerobes

naerob

es

Faculta

tive

erob

es

aerophiles

erotoleran

aerobe

s

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these thioglycolatebroth culturesreveals the O2requirements foreach of the

bacteria.

O Ae

An Fa A

e

Mic

roa

Aer

Ana

Special techniques are needed to growaerobic & anaerobic microorganisms in the

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aerobic & anaerobic microorganisms in thelaboratory.

Aerobes-

culture medium must be oxygenated byshaking or bubbling air into the medium.

Bottles or tubes can be

Anaerobes need O2 to be excluded.

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Bottles or tubes can be

filled completely withmedia & sealed with ascrew cap.

Reducing agents(thioglycolate) can beadded to convert all O2to water.

Anoxic jars with apalladium catalystconvert O2 to water.

For obligate anaerobes that die if exposedto O2 media must be boiled a reducing

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to O2, media must be boiled, a reducingagent added, then sealed under an O

2

-freeH2 or N2 gas.

Work with these cultures must be done in

an anoxic environment that can be providedby anoxic glove boxes.

Toxic Forms of Oxygen Several toxic forms of oxygen or molecules that

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Several toxic forms of oxygen or molecules thatcontain oxygen can be formed in the cell during

normal cellular processes:Singlet oxygen 1O2 produced by peroxidases

Superoxide anion O2-

Hydrogen peroxide H2O2Hydroxyl radical -OH

generated duringthe reduction ofoxygen to water

Enzymes made by cells can neutralize toxicforms of oxygen.

Catalase, peroxidase, superoxide dismutase,

superoxide reductase

These reactions generate

reactive oxygen species

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reactive oxygen species

(toxic oxygen products)

These reactions

destroy ROS

Controlling Microbial GrowthPhysical AgentsTemperature

f

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Pasteurization- 63C for 30 minutes

Flash pasteurization- 72C for 15 seconds does NOT kill all cells reduces microbial load (# of viable

organisms) kills most pathogens; inhibits spoilagemicrobes

UHTUltra-high temperature 150C for 3 seconds Sterilizesall bacteria killed

creamer boxed milk

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Physical AgentsOther Methods

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Cold temperature

Refrigeration Freezing

Slows growth, does not kill all bacteria

Physical AgentsOther Methods

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Irradiation

Microwaves thermal effects Ultraviolet radiation DNA damage

X-rays

gamma rays

Ionizingradiation

nucleic acid andprotein damage

Ultraviolet radiation used to decontaminate surfaces & materials

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that do not absorb light (air & water)

Causes thymine dimers in DNA.UV hood air isblown outward

through a filter fromthe back and fromedges of the hood so

that the area insidethe hood remainssterile once the UVlight is turned off.

Ionizing radiation

Gamma rays & X rays

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Gamma rays & X-rays

penetrates solid or light-absorbingmaterials

widely used for sterilization &

decontamination(treatment of an objector surface to make it safe to handle) inmedical & food industries

Causes breaks in DNA; breaks hydrogenbonds & disulfide bridges in proteins

Physical AgentsOther MethodsFiltration

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Filter-device with pores too small for

microorganisms to fit through but largeenough for liquid or gas to pass through.

Physical AgentsOther MethodsFiltration

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Filter-device with pores too small for

microorganisms to fit through but largeenough for liquid or gas to pass through.

Filters remove microorganisms from air or

liquids that are heat sensitive. 2 types: depth & membrane

Depth filters fibrous sheets or mats made from a random

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array of overlapping paper, asbestos, or

borosilicate traps large particles from liquids & airExamples

HEPA filters Home air/heat system Vacuum cleaner UV hood Clean rooms and isolation rooms for

quarantine

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Membrane filters thin sheets of polymers (cellulose); contain

tiny holes of known size

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tiny holes of known size

Act like sieves, trap particles on membranesurface Antibiotics & other pharmaceuticals

Nucleation track (Nucleopore) filtersused for concentrating a liquid samplefor view on the scanning electronmicroscope.

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Chemical Agents Disinfectants

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Disinfectants

used to reduce microbial numbers onnonliving material

bleach (chlorine), ethanol

Antiseptics used to reduce microbial numbers on living

tissues

Betadyne (iodine), H2O2

Chemical AgentsAntibiotics

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naturally occurring antimicrobial substancesproduced by microorganisms

Many known but less than 1 % clinicallyuseful because of poor uptake or toxicity.

Selectively kills microbes

May not work on all species

Interferes with bacterial-specific enzymes Cell wall synthesis

Bacterial ribosome

Penicillin Many derivatives

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Blocks cell wallsynthesis

Growing bacteria lyse

Slow-growingbacteria takelonger to die

Biological Agents Probiotics

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Good bacteria Displace pathogens from tissues

Bacteriophage

Phage Viruses that infect bacteria Do not harmeukaryotes