Chapter 4: Dynamics of Prokaryotic Growth

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Chapter 4Dynamics ofProkaryoticGrowth
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Important Point
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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
  by-products (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.

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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 95C and solidifies below 45C.
• 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.

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(mostly) Isolated Colonies
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Streak-Plate Method
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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

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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.
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Environmental Factors
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Optimum Growth Temperature
Growth temperature optimum.
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Temperature Ranges
Max due to enzyme denaturation.
Min due to enzyme membrane fluidity problems.
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Psychotrophs
Important for food spoilage.
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Mesophiles
Most human pathogens are mesophiles.
I.e., organisms adapted to growth at body
temperature.
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Thermophiles
Important source of heat-stable enzymes (e.g.,
Taq polymerase or laundry detergent enzymes).
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Oxygen Requirements The Shake Tube
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Oxygen Requirements The Shake Tube
Aerotolerant Anaerobe!
Note maximum growth nearer to surface (where
oxygen is plentiful this is not shown well in
image).
Dont worry about enzyme names. Just recall O2
(product) detoxification.
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Medically Important Examples
Pseudomonas spp. are obligate aerobes.
E.g., Clostridium spp. such as C. botulinum.
Enterics such as Escherichia coli are facultative
anaerobes
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Water Availability
Plasmolysis
Food preservation jams, jellies, bacon,
anchovies, etc.
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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.

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Energy Carbon Source Types
Chemoautotroph is good enough for now.
Chemoheterotroph 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.
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Culture Media Types
Peptone predigested protein
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Culture Media Types
Note that, confusingly, many media are both
selective and differential, e.g., MacConkey agar.
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Enrichment Culture
Means of isolating rare organisms with specific
characteristics from heterogeneous populations.
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Direct Microscopic Count
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Direct Microscopic Count
Requires relatively high bacterial densities.
Usually cant distinguish living cells from dead
cells.
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Viable Counts Plate Counts
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Viable Counts Plate Counts
Quantifies number of cells (CFUs) capable of
replicating.
Note the enumeration of colony-forming units
(CFUs).
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Serial Dilutions
Note Serial Dilution.
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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.
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Most Probable Number (MPN)
Useful particularly when enumerating organisms
that wont grow on/in agar media.
Durham tube.
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Growth Curve
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Growth Curve
Constant per-capita death rate (exponential).
Death rate Birth rate.
Division at constant rate (exponential).
Time of gearing up for division following change
in culture conditions.
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Phase of Prolonged Decline
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Continuous Culture, Chemostat
Chemostats are a means of keeping a culture in
log phase indefinitely.
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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.

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Chapter 6 Notes

• Dont 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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