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Chapter 6
Microbial Nutrition and
Growth
Microbiology
FUNDAMENTALS
A Clinical Approach
Fourth Edition
Marjorie Kelly Cowan
Heidi Smith
Jennifer Lusk
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Learning Outcomes Section 6.1
1. List the essential nutrients of a bacterial cell.
2. Differentiate between macronutrients and micronutrients.
3. List and define four different terms that describe an organism’s
sources of carbon and energy.
4. Define saprobe and parasite, and explain why these terms can be an
oversimplification.
5. Compare and contrast the processes of diffusion and osmosis.
6. Identify the effects of isotonic, hypotonic, and hypertonic conditions
on a cell.
7. Name two types of passive transport and one type of active transport.
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2
Microbial Nutrition – Review of Terms
Essential nutrient
• any substance that must be provided to an organism
Macronutrients
• required in relatively large quantities and play principal
roles in cell structure and metabolism
Micronutrients
• present in much smaller amounts and are involved in
enzyme function and maintenance of protein structure
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3
Categorizing Nutrients According to Their Carbon
Content - Review of Terms
Inorganic nutrients
• an atom or simple molecule that contains a combination of
atoms other than C and H
Organic nutrients
• contain carbon and hydrogen atoms and are usually the
products of living things
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4
Table 6.1
5
What Microbes Eat – Review of Terms
Heterotroph: an organism that must obtain its carbon in an
organic form
Autotroph: an organism that uses inorganic CO2 as its
carbon source
Phototroph: microbe that photosynthesizes
Chemotroph: microbe that gets its energy from chemical
compounds
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6
Table 6.2
7
Table 6.3
8
How Microbes Eat: Transport Mechanisms – Review of Terms
Transport of necessary nutrients occurs across the
cytoplasmic membrane, even in organisms with cell walls
Diffusion
• atoms or molecules move in a gradient from an area of
higher density or concentration to an area of lower
density or concentration
Osmosis
• the diffusion of water through a selectively, or
differentially, permeable membrane
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9
Osmosis
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10
Cell Responses to Osmosis
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11
Transport Processes in Cells
Passive
Active
Examples
Description
Energy Requirements
Simple
diffusion
A fundamental property of
atoms and molecules that
exist in a state of random
motion
None. Substances move
on a gradient from higher
concentration to lower
concentration.
Facilitated
diffusion
Molecule binds to a
specific receptor in
membrane and is carried
to other side. Moleculespecific. Goes both
directions. Rate of
transport is limited by the
number of binding sites on
transport proteins.
None. Substances
move on a gradient
from higher
concentration to
lower
concentration.
Carriermediated
active
transport
Atoms or molecules are
pumped into or out of the
cell by specialized
receptors.
Driven by ATP
or the proton
motive force
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12
Endocytosis: Eating and Drinking by Cells – Review of
Terms
Endocytosis
• cell encloses the substance in its membrane
• simultaneously forms a vacuole and engulfs the substance
• Phagocytosis
• accomplished by amoebas and white blood cells
• ingest whole cells or large solid matter
• Pinocytosis
• ingestion of liquids such as oils or molecules in solution
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13
Concept Check
Which of the following terms describes an organism that
derives its energy and carbon from organic molecules?
A. Photoautotroph
B. Chemoheterotroph
C. Lithoautotroph
D. Chemoautotroph
E. Photoheterotroph
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14
Learning Outcomes Section 6.2
8. List and define five terms used to express the
temperature-related growth capabilities of microbes.
9. Summarize three ways in which microorganisms function
in the presence of differing oxygen conditions.
10. Identify three important environmental factors (other than
temperature and oxygen) with which microorganisms
must cope.
11. List and describe the five types of associations microbes
can have with their hosts.
12. Discuss characteristics of biofilms that differentiate them
from planktonic bacteria.
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15
Cardinal Temperatures
• Minimum temperature
• the lowest temperature that permits
a microbe’s continued growth and
metabolism - below this
temperature, its activities stop
• Maximum temperature
• the highest temperature at which
growth and metabolism can proceed
before proteins are denatured
• Optimum temperature
• an intermediate between the
minimum and the maximum that
promotes the fastest rate of growth
and metabolism
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16
Psychrophiles
• optimum temperature
below 15°C
• capable of growth at 0°C
• obligate with respect to
cold and cannot grow
above 20°C
Psychrotolerant
• grow slowly in the cold but
have an optimum
temperature between
15°C and 30°C
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17
Figure 6.5
18
Mesophiles
• majority of medically significant microorganisms
• grow at intermediate temperatures between 20°C and
40°C
• human pathogens have optimal temperatures between
30°C and 40°C
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19
Thermoduric Microbes
• can survive short exposure to high temperatures but are
normally mesophiles
• common contaminants of heated or pasteurized foods
• Examples are heat-resistant endospore formers such as
Bacillus and Clostridium
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20
Thermophiles
• grow optimally at temperatures greater than 45°C
• live in soil and water associated with volcanic activity,
compost piles, and in habitats directly exposed to the sun
• vary in heat requirements with a range of growth of 45°C
to 80°C
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21
UnFigure 6.13
22
Gases
O2 and CO2 - atmospheric gases that influence microbial growth
• O2
• has the greatest impact on microbial growth
• an important respiratory gas
• a powerful oxidizing agent
Three categories of microbes
1. those that use oxygen and detoxify it
2. those that can neither use oxygen nor detoxify it
3. those that do not use oxygen but can detoxify it
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23
How Microbes Process Oxygen
As oxygen enters cellular reactions, it is transformed into
several toxic products
• Singlet oxygen (O)
• Hydrogen peroxide
(H2O2)
• an extremely reactive
molecule
• build up can damage and
destroy a cell by the
oxidation of membrane lipids
• Superoxide ion (O2
–)
• toxic to cells and used as a
disinfectant
• Hydroxyl radical (OH–)
• highly reactive
• highly reactive
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24
How Microbes Protect Themselves Against Damage from
Oxygen By-products
Most cells have developed enzymes that scavenge and
neutralize reactive oxygen by-products
• Two-step process requires two enzymes:
Superoxide
dismutase
Step 1. 2O 2  2H  
 H 2 O 2 (hydrogen peroxide)  O 2
Step 2.
Catalase
2H 2 O 2 
 2H 2O  O 2
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25
Oxygen Usage and Tolerance Patterns in Microbes (1)
Aerobes
• can use gaseous oxygen in their metabolism
• possess the enzymes needed to process
toxic oxygen products
• an organism that cannot grow without
oxygen is an obligate aerobe
Microaerophiles
• are harmed by normal atmospheric
concentrations of oxygen
• but require a small amount of it in
metabolism
Facultative anaerobes
• do not require oxygen for metabolism
• but use it when it is present
(Top) Source: CDC/Laura Rose & Janice Haney Carr (Aerobess); (Bottom) Heather Davies/Science Source (Microaerophiles)a
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26
Oxygen Usage and Tolerance Patterns in Microbes (3)
Anaerobes
• lack the metabolic enzyme systems for using
oxygen in respiration
• Obligate anaerobes also lack the enzymes
for processing toxic oxygen and die in its
presence
Aerotolerant anaerobes
• do not utilize oxygen
• but can survive and grow to a limited extent in
its presence
• not harmed by oxygen, mainly because they
possess alternate mechanisms for breaking
down peroxides and superoxide
(Top) Source: CDC/Janice Carr (Anaerobes); (Bottom) Janice Haney Carr/CDC (Aerotolerant anaerobes)
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27
Figure 6.6
28
Carbon Dioxide
Capnophiles
• organisms that grow
best at a higher CO2
tension than is
normally present in
the atmosphere
• growing specimens
in clinical settings
require higher CO2
tension
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29
pH
• the degree of acidity or alkalinity of a solution
• expressed by the pH scale – 0 - 14
• 7.0 is the pH of pure water
• pH value decreases - the acidity increases
• pH value increases - the alkalinity increases
The majority of organisms live or grow in habitats between
pH 6 and 8
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30
pH Extremes
Acidophiles
Alkalinophiles
• organisms that thrive in
acidic environments
• organisms that thrive in
alkaline conditions
• Euglena mutabilis
• Natronomonas
• grows in acid pools between
pH 0 and 1
• Thermoplasma
• lives in coal piles at a pH of 1
or 2
• live in hot pools and soils up
to pH 12
• Proteus
• can create alkaline
conditions to neutralize urine
and colonize and infect the
urinary system
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31
Osmotic Pressure
Osmophiles
• live in habitats with high solute
concentration
Halophiles: prefer high concentration of
salt
• Obligate halophiles
• grow optimally at solutions of 25% NaCl but
require at least 9% NaCl
• Facultative halophiles
• remarkably resistant to salt
• though they do not normally reside in high salt
environments
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32
Radiation
• phototrophs use visible light rays as an energy source
• nonphotosynthetic microbes tend to be damaged by the
toxic oxygen products produced by contact with light
• some microbial species produce yellow carotenoid
pigments to absorb and dismantle toxic oxygen
• ultraviolet and ionizing radiation can be used in microbial
control
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33
Pressure
Barophiles
• exist under pressures that range from a few times to over
1,000 times the pressure of the atmosphere
• these bacteria are strictly adapted to high pressures
• they will rupture when exposed to normal atmospheric
pressure
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34
Other Organisms
In all but the rarest instances, microbes live in shared
habitats:
• Associations
• between similar or dissimilar types of microbes
• with multicellular organisms, such as animals or plants
• Interactions
• can be beneficial, harmful, or have no particular effect
• can be obligatory or nonobligatory to the members
• often involve nutritional interactions
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35
Strong Partnerships: Symbioses
Symbiosis
• general term to denote a situation in which two organisms
live together in a close partnership
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36
Associations but Not Partnerships
Antagonism
• an association between free-living species that arises when
members of a community compete
Synergism:
• an interrelationship between two organisms that benefits them but
is not necessary for survival
• cooperate to produce a result that neither could do alone
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37
Steps in Biofilm Formation
Ellen Swogger and Garth James, Center for Biofilm Engineering, Montana State University
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38
Concept Check 2
Which of the following describes partnership
between microbes in which one organism is
benefited and one is harmed in some way?
A. Mutualism
B. Synergism
C. Commensalism
D. Parasitism
E. Antagonism
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39
Learning Outcomes Section 6.3
13. Summarize the steps of bacterial binary fission.
14. Define doubling time, and describe how it leads to
exponential growth.
15. Compare and contrast the four phases of growth in a
bacterial growth curve.
16. Identify one culture-based and one non-culture-based
method used for analyzing bacterial growth.
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40
The Study of Bacterial Growth
Binary fission
• one cell becomes two
• parent cell enlarges
• duplicates its
chromosome
• starts to pull its cell
envelope together to
the center of the cell
• cell wall eventually
forms a complete
septum
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41
Rate of Population Growth
Generation time/
doubling time
• the time required for
a complete fission
cycle
• from parent cell to
two daughter cells
• Generation
• increases the
population by a
factor of two
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42
Length of Generation Time
• a measure of the growth
rate of an organism
• average generation time
is 30 to 60 minutes
• shortest generation
times can be 10 to 12
minutes
• most pathogens have
relatively short
generation times
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43
The Mathematics of Population Growth
The size of a
population can be
calculated by the
following equation
Nt = (N)2n
•
Nt - total # of cells in the
population - t denotes “at
some point in time”
•
N - represents the starting
number of cells
•
exponent n - denotes the
generation number
•
2n - represents the number
of cells in that generation
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44
Mathematics of Population Growth
45
The Population Growth Curve
Growth curve
• a predicable pattern of a bacterial population growth in a
closed system
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46
Growth Curve in Bacterial Culture
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47
The Practical Importance of the Growth Curve
Important implications in controlling microbes in the
environment
• microbes in the exponential growth phase are more
vulnerable to antimicrobial agents and heat
• cells in the growth phase are more vulnerable to
conditions that disrupt cell metabolism and binary fission
• in general, actively growing cells are more vulnerable to
growth inhibition and destruction
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48
Analyzing Population Size Without Culturing: Turbidity
Turbidity/turbidometry
• clear nutrient solution becomes turbid, or cloudy, as
microbes grow in it
• the greater the turbidity, the larger the population size
Turbidity Measurements as
Indicators of Growth
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49
UnFigure 6.20
50
Analyzing Population Size Without Culturing
Counting
• Direct cell count
Direct Microscopic Count of Bacteria
• measured
microscopically
• Coulter counter
• electronically
scans a fluid as
it passes
through a tiny
pipette
Coulter Counter
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51
UnFigure 6.21
52
Concept Check 3
Put the steps of the bacterial growth curve in the
correct order.
A. Death phase
B. Lag phase
C. Exponential phase
D. Stationary phase
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