Chapter 6
Microbial
Nutrition and
Growth
Growth Requirements
• Microbial growth
– Increase in a population of microbes
• Result of microbial growth is discrete colony
– An aggregation of cells arising from single parent
cell
• Reproduction results in growth
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Growth Requirements
• Organisms use a variety of nutrients for
their energy needs and to build organic
molecules and cellular structures
• Most common nutrients contain
necessary elements such as carbon,
oxygen, nitrogen, and hydrogen
• Microbes obtain nutrients from variety of
sources
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Growth Requirements
• Associations
– Organisms live in association with different species
– Antagonistic relationships
– Synergistic relationships
– Symbiotic relationships
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Growth Requirements
• Biofilms
– Complex relationships among numerous
microorganisms
– Develop an extracellular matrix
– Adheres cells to one another
– Allows attachment to a substrate
– Sequesters nutrients
– May protect individuals in the biofilm
– Form on surfaces often as a result of quorum
sensing
– Many microorganisms more harmful as part of a
biofilm
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Figure 6.17 Binary fission events-overview
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Growth of Microbial Populations
ANIMATION Binary Fission
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Figure 6.18 Comparison of arithmetic and logarithmic growth-overview
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Growth of Microbial Populations
• Generation Time
– Time required for a bacterial cell to grow
and divide
– Dependent on chemical and physical
conditions
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Figure 6.19 Two growth curves of logarithmic growth-overview
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Number of live cells (log)
Figure 6.20 Typical microbial growth curve
Stationary phase
Log
(exponential)
phase
Death
(decline)
phase
Lag phase
Time
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Figure 6.21 Schematic of chemostat
Fresh medium with
a limiting amount
of a nutrient
Flow-rate
regulator
Sterile air
of other
gas
Culture
vessel
Culture
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Overflow
tube
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Growth of Microbial Populations
• Measuring Microbial Reproduction
– Direct methods
– Serial dilution and viable plate counts
– Membrane filtration
– Most probable number
– Microscopic counts
– Electronic counters
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Figure 6.22 Estimating microbial population size-overview
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Figure 6.23 Use of membrane filtration to estimate microbial population-overview
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Figure 6.24 The most probable number (MPN) method for estimating microbial numbers
1.0 ml
Undiluted
1.0 ml
1:10
1:100
Inoculate 1.0 ml into
each of 5 tubes
Phenol red, pH
color indicator,
added
Incubate
Results
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1 tube positive
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Figure 6.25 The use of a cell counter for estimating microbial numbers-overview
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Growth of Microbial Populations
• Measuring Microbial Growth
– Indirect methods
– Metabolic activity
– Dry weight
– Turbidity
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Figure 6.26 Spectrophotometry-overview
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Growth of Microbial Populations
• Measuring Microbial Reproduction
– Genetic methods
– Isolate DNA sequences of unculturable
prokaryotes
– Used to estimate the number of these
microbes
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Case Study–Can a trip to the dentist be life threatening?
•
•
•
•
•
•
Details of the case
Why do we get our teeth cleaned?
Why does Betty feel so bad?
What has happened?
Will the biofilm return?
How did they figure out Betty had septicemia?
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