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Chapter 4:
Dynamics of
Prokaryotic
Growth
Important Point:
Each Species is Unique
 Bacteria are incredibly diverse, but...
 Each bacterial species can grow in only a limited
set of environments.
 Each bacterial species can grow only if
presented with the right nutrients/conditions.
 In addition, bacteria produce characteristic byproducts (e.g., waste products).
 We can take advantage of these growth
characteristics to identify bacteria phenotypically.
 To do these identifications we first have to get
organisms in Pure Culture.
 Unfortunately, only about 1% of microorganisms
currently can be grown in pure culture.
Pure-Culture Basics
 Sterile = completely free of microbes.
 Aseptic Technique = procedures that minimize
unintentional introduction of microorganisms to
media (cultures) or from cultures to surrounding
environment.
 Solid media is usually employed to obtain pure
cultures.
 Agar is usually employed to make solid media.
 Agar melts at 95°C and solidifies below 45°C.
 Colony = pile of cells descended from single cell (or
clump of cells).
 Petri Dish = container to which agar is added to
obtain pure culture.
 Agar Plate (plate) = agar-containing petri dish.
(mostly) Isolated Colonies
Streak-Plate Method
Storing Pure Cultures
 Stored pure cultures are often called “Stock
Cultures”
 Stock cultures often are stored as/using:
 Frozen in glycerol solution
 Lyophilized = freeze drying
 On agar slants
 As stabs
Binary Fission
This is how most
bacteria undergo
cell division (how
they replicate).
The interval,
division to division,
is called the
Generation or
Doubling Time.
Note that not all
daughter cells fully
separate after
division, e.g.
streptococci, etc.
Environmental Factors
Optimum Growth Temperature
Growth
temperature
optimum.
Temperature Ranges
Max due to
enzyme
denaturation.
Min due to
enzyme &
membrane
fluidity
problems.
Psychotrophs
Important for
food
spoilage.
Mesophiles
Most human
pathogens are
mesophiles.
I.e., organisms adapted
to growth at body
temperature.
Thermophiles
Important source of heatstable enzymes (e.g.,
Taq polymerase or
laundry detergent
enzymes).
Oxygen Requirements: The Shake Tube
Oxygen Requirements: The Shake Tube
Note maximum growth
nearer to surface
(where oxygen is
plentiful; this is not
shown well in image).
Aerotolerant Anaerobe!
Don’t worry about
enzyme names. Just
recall “O2 (product)
detoxification”.
Medically Important Examples
Pseudomonas spp.
are obligate aerobes.
E.g., Clostridium spp.
such as C. botulinum.
Enterics such as Escherichia coli are
facultative anaerobes
Water Availability
Plasmolysis
Food preservation: jams, jellies, bacon, anchovies, etc.
Terms for Nutrient Needs
 Heterotrophs = require organic carbon (e.g.,
glucose).
 Autotrophs convert CO2 to organic carbon.
 Carbon fixation = conversion of CO2 to organic
carbon.
 Nitrogen fixation = conversion of N2 to non-gaseous
form (i.e., ammonia).
 Growth factors = small organic molecules (e.g.,
vitamins, amino acids) that must be provided for
growth (some bacteria require no “exogenous” “growth
factors”).
 E.g., Neisseria spp. can require 40 growth factors to
grow. We would describe such a bacterium as
fastidious.
 E. coli requires no growth factors. We would describe
such a bacterium as non-fastidious.
Energy & Carbon Source Types
“Chemoheterotroph” is
good enough for now.
“Chemoautotroph”
is good enough for
now.
Chemoheterotrophs differ in the number (and types) of organic
compounds they can use. Some Pseudomonas species can utilize 80
different compounds. Other bacteria are limited to as little as only a
single organic compound type.
Culture Media Types
Peptone = predigested protein
Culture Media Types
Note that, confusingly, many media are both
selective and differential, e.g., MacConkey agar.
Enrichment Culture
Means of isolating rare
organisms with specific
characteristics from
heterogeneous
populations.
Direct Microscopic Count
Direct Microscopic Count
Requires relatively high
bacterial densities.
Usually can’t distinguish
living cells from dead cells.
Viable Counts: Plate Counts
Viable Counts: Plate Counts
Note the
enumeration
of colonyforming
units
(CFUs).
Quantifies
number of
cells (CFUs)
capable of
replicating.
Serial Dilutions
Note
Serial
Dilution.
Most Probable Number (MPN)
These are gas-filled
tubes, an indication
of bacterial growth
(fermentation).
Looking for
sufficient dilution
that ~half of tubes
show growth.
Reciprocal of
that dilution 
bacterial
density.
Most Probable Number (MPN)
Useful particularly
when enumerating
organisms that
won’t grow on/in
agar media.
Durham tube.
Growth Curve
Growth Curve
Death rate = Birth
rate.
Constant per-capita death
rate (exponential).
Division at constant rate
(exponential).
Time of gearing up for
division following change in
culture conditions.
Phase of Prolonged Decline
Continuous Culture, Chemostat
Chemostats are a
means of keeping
a culture in log
phase indefinitely.
Biofilms
 Biofilms are polysaccharide-encased bacterial
communities attached to environmental surfaces.
 Biofilms include slippery rocks (in aquatic
environments), slime coating sink drains, yuck
yucking up what was once your clean toilet bowl,
tarter on your teeth, etc.
 “It is estimated that 65% of human bacterial
infections involve biofilms.”
 “Biofilms are particularly troublesome because
they protect organisms against harmful
chemicals such as disinfectants” and antibiotics.
 They can accumulate on non-sterile medical devices
kept in contact with patients over relatively long
periods, e.g., on catheters.
Chapter 6 Notes
 Don’t worry too much about the
details of Glycolysis, Cellular
Respiration, or Photosynthesis
onward.
 These topics are covered on pp.
144-151 and pp. 156-163.
 Note, however, that we will cover
Glycolysis and Cellular Respiration
in class at least from the
perspectives of the importance of
NAD+ regeneration.
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