Transcript Microbiology_Ch_05_W2010 - Cal State LA

Chapter 5
Lecture Outline
Environmental Influences and
Control of Microbial Growth
Environmental Limits on
Microbial Growth
Temperature
 pH
 Osmolarity
 Oxygen
 Pressure

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-phile means “MUST have” and not “likes it”
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Changes in Temperature



Microbes cannot control their own temperature
Growth rate increases with temperature
Proteins denature if temperature too high

Microbial proteins adapted to temperature range:

Psychrophiles


Mesophiles


12°C–45°C
Thermophiles


Cold: below 20°C
40°C–80°C
Extreme thermophiles


Hyperthermophile
65°C–113°C
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Psychrophile Environment
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Example for a Psychrophile
Microorganism
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Halorubrum lacusprofundi
Extremophile
Haloarchaeon
Found in subzero temperatures in
5 M NaCl
Proteins more flexible and need
less energy to function
High content of unsaturated fatty
acids makes membrane more fluid
Model system for astrobiology
Want to know more about astrobiology?
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http://www.atomseek.com/Astronomy/Extraterrestrial_Life/Exobiology/Geobiology_and_Astrobiology_at_Caltech/JPL_L90130
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Thermophilic and
Hyperthermophilic Environments
Yellow Stone National Park: hot spring
Hydrothermal vent in deep ocean
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Example for a Hyperthermophile
Microroganism
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Thermus aquaticus
First source for DNA
polymerase used fro PCR
amplification of DNA
Stable enzymes due to
decreased glycine
content
Stabilizing DNA binding
proteins
More saturated fatty acids
in membrane
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Response to Temperature

Heat shock response




Occurs at high end of temperature
range
“Emergency” proteins produced
Help keep proteins from denaturing
Induced by many stressful conditions
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Response Analysis to Stress
Heat
High salt concentrations
Arid conditions
Cold shock response
Red: genes up in condition 1 only
Green: genes up in condition 2 only
Orange-yellow: no change in gene
expression
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Variations in Pressure

Barophiles
 Adapted


to high pressures
Up to 1,000 atm
Barotolerant organisms
 Grow
at high, but not very high
pressure

Barosensitive organisms
 Die

at high pressure
Most “typical” bacteria, all mammals
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Barophilic Environment

Example: Shewanella violacea

Either psychrophile or
hyperthermophile
High levels of polyunsaturated
fatty acids

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Changes in Water Activity and Salt
Concentration
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Water activity relates to water availability
Solutes raise osmolarity
High osmolarity reduces available water or water activity
Osmotic pressure can burst membranes

Low osmotic pressure outside cell
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

Mechanosensitive channels relieve stress
Release cell contents
High osmotic pressure outside cell
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Cells synthesize osmolytes to counter balance
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
Proline, glutamic acid
Increase internal osmolarity
Global response
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Halophiles


Archaea
Require high concentration of NaCl

2–4 M (= 10 - 20% NaCl)
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
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Intracellular salt level is NOT high
Pump out salt



sea water: contains ~ 3.5% NaCl
Na+/K+ antiport
Live in salt seas
Often reddish pigments
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Changes in pH

Enzymes only work in narrow pH range
 Amino


pH levels alter concentration of H+
Bacteria regulate internal pH
 When

acids must have correct charges
environment is in similar pH range
Weak acids can pass through membranes
 Disrupt
cell pH homeostasis, kills cells
 Good food preservatives
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Classification of Organisms
Grouped by Optimal Growth pH
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pH Homeostasis
Acid added at a
constant rate
Base added at a
constant rate
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Changes in pH

Neutralophiles
 Grow
at pH 5–8
 Include bacteria in gut

Acidophiles
 Grow
Sulfolobulus acidocaldarius
60 – 95°C, pH 1-5
at pH 0–5
Some grow in stomach acid
 Some in sulfuric acid springs


Alkalophiles
 Grow

at pH 9–11
Found in soda lakes
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Sulfur Caldron acid spring
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pH Change can Trigger UpRegulation of Virulence factor
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Microbial Responses to Oxygen


Has microbe the
machinery that allows to
deal with oxygen radials?
Terminal electron
acceptor is oxygen.


Respiration
Terminal electron
acceptor is a an organic
endogenous compound

fermentation
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Oxygen as Electron Acceptor

Aerobes–O2 is ultimate electron acceptor
 Very
strong electron acceptor
 Can oxidize, damage proteins

Anaerobes
 Reactive


oxygen species (ROS) produced
Oxidize, damage proteins
Microaerophiles
 Can

tolerate low levels of O2
Catalase inactivates ROS
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Other Electron Acceptors

Anaerobes pass electrons to different
ultimate electron acceptors
 Anaerobic

respiration
Inorganic electron acceptors

Nitrate nitrite, thiosulfate
 Fermentation


Organic electron acceptors
Thrive in anaerobic environments
 Early
Earth, deep water, lower gut
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Oxygen-related Growth Zones
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Anaerobic Growth Technology
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Nutrient Deprivation, Starvation
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Lack of nutrients slows cell metabolism
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Accumulation of smallsignaling molecules
(e.g., cAMP)
Global change in gene expression
Stimulates stress responses
Daughter cells become smaller
Cells spread farther
Sporulation
Starving E. coli
Starving Pseudomonas
Oligotrophs



Most microbes in nature
Efficiently absorb N2, PO4 from nutrient-poor
(low in organic material) environments
May commit suicide in high nutrient
environments
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Maintaining Microbial Diversity
through Nutrient Limitation
A transports
nitrogen poorly
but phosphate
efficiently
B transports
phosphate poorly
but nitrogen
efficiently
A and B have enough
phosphate but B has
still advantage of
better nitrogen uptake.
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Control of Microbial Growth
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Antimicrobial Growth Measures
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Sterilization
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Disinfection
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Killing or removal of DISEASE PRODUCING organisms (on nonanimated surfaces)
Antisepsis

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ALL living cells including spores, dormant forms, and viruses
eliminated
Killing or removal of DISEASE PRODUCING organisms on
animated surfaces
Sanitation

Reducing the microbial population to a SAFE LEVEL for the
public
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Control of Microbial Growth

Physical
 Temperature
 Cold
 Heat
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Pasteurization
Sterilzation
 Pressure
 Drying (lyophilization)
 Filtration
 Irradiation


Chemical
Biological
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Controlling Microbial Growth
Microbes die at logarithmic rate
 D-value = Decimal reduction time
 D-value = time to kill 90% of cells

2
D-values =
time to kill
99% of cells

Antimicrobial agents decrease D-value
 Kills
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cells faster
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Physical Measures to Control
Microbial Growth

Temperature
 Heat
 Pasteurization
 Sterilization
 Cold

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

Pressure
Drying (lyophilization)
Filtration
Irradiation
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Physical Agents: Pasteurization

Heating food to remove disease causing and
reduces spoilage microorganisms

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Low Temperature Long Time
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
Lead organisms are Mycobacterium tuberculosis and
Coxiella burnetti
63°C for 30 minutes
High Temperature Short Time (Flash
pasteurization)

72°C for 15 seconds

Pasteurization treatments do NOT kill all cells



Does not
sterilize
Pasteurized food spoils eventually
Leaves food tasting normal
UHT—Ultra-high temperature

150°C for 3 seconds

Used for creamers
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Sterilizes
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Physical Agents: Autoclave
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Moist heat more effective than dry heat
Autoclave = steam cooker
High temperature under pressure
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121°C, 15 psi (2 atm) for
20 minutes
Sterilizes

Kills all bacteria
 Kills endospores

Clostridium botulinum


Botulism
Bacillus anthracis

Anthrax
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Physical Agents: Dry Heat
2 – 3 hrs 160 – 170° C
 Sterilization
 Prevents corrosion
 Suited also for powders

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Physical Agents: Cold

Refrigeration (4 – 8°C)
 Slows
growth, does not kill all bacteria
 Not: microorganisms die slower too!
 Most pathogens are mesophilic


Exception: Listeria monocyogenes
Freezing
 Kills
some worms
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Physical Agents: Filtration
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0. 2 mm
Removes most bacteria
Does not remove cell wall
less bacteria
Does not remove viruses
Used for liquids and air
 May
remove solutes that
adhere to the filters
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Physical Agents: Irradiation


DNA damage
UV
 Only
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

Deinococcus radiodurans
for surface sterilization
X-rays
g-rays
Electron beams
Not suited for viruses and
prions
Would survive atomic bomb
Extensive DNA repair mechanisms
Used in bioremediation
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Chemical Agents
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Chemical Agents: Factors
Influencing Efficacy
Presence of organic matter (as less as
better)
 Composition of microbial load
 Chemical stability of the agent
 Surface tension (should be low)

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Chemical Agents: Disinfectants



Liquid
Gaseous
Kill microbes but destroys eukaryotic cells as
well


Cannot be used inside patients
Example: halogens
 Iodine,
chlorine
 Highly reactive
 Damage protein, lipids and DNA
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Chemical Structures and Microbial
Targets of Selected Disinfectants
Disruption of
membranes
Protein
denaturation
Proteins
Lipids
Proteins
Nucleic acids
Membranes
Protein
denaturation
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Protein
Rapid
penetration
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Chemical Agents

Antibiotics
 Will
be covered later
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Biological Agents

Probiotics
 “Live
bacteria ingested to the
benefit of health


Displace disease
organisms from tissues
Bacteriophages
 “Phages”
 Viruses
that
attack bacteria

Do not harm
eukaryotes
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Concept Quiz
Microbes that grow at temperatures between
40°C and 80°C are called
psychrophiles.
b. mesophiles.
c. thermophiles.
d. extreme thermophiles.
a.
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Concept Quiz
Bacteria cannot grow in solutions with very
high concentrations of sugar because
bacteria cannot digest pure sugar.
b. sugar raises the solution’s osmolarity.
c. sugar alters the solution’s pH.
a.
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Concept Quiz
Physical agents to prevent bacterial growth
include
pasteurization, freezing, phages.
b. irradiation, probiotics, filtration.
c. autoclaving, irradiation, freezing.
d. antibiotics, refrigeration, pasteurization.
a.
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