I. Microbial growth II. Environmental effects on microbial growth

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I. Microbial growthII. Environmental effects on
microbial growth
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I. Microbial growth

• A. Exponential growth and how to calculate it
• B. Growth curve of bacteria in culture
• C. Measuring cell growth
• D. Continuous culture

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I. Microbial growth

• A. Exponential growth and how to calculate it

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Exponential growth
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Text Fig. 7.16
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Generation time

• Generation time (g) (or Doubling time) -- the
  time required for a population of cells to
  ___________. Or the time required for one cell
  to become ______.

For this example, g ___________
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Estimating generation times
___ hr
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Estimating generation times (cont.)
___ hr
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Calculating generation times (g)
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Notice the simple geometric progression of the
number 2
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Calculating generation times (cont.)

• Because of this geometric progression, there is a
  direct, predictable relationship between the
  number of cells in a culture ________ and the
  number there ___________ a period of exponential
  growth
• Nf
• Where Nf is the ________ cell number
• Ni is the_________ number of cells
• n is the _______________________

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Calculating generation times (cont.)

• Nf (Ni)2n
• So, if we start with 20 Salmonella cells in a
  potato salad sitting on your warm kitchen
  counter, with a 30 minute generation time, how
  many cells will there be after 8 hours? To get
  the of generations (n), divide 8 hours by 30
  minutes to get 16
• Nf (20)2 ___
• Nf (20)(_______) 1,310,720 cells

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• A single bacterium with a generation time of 20
  minutes would, growing exponentially for 48
  hours, produce a population weighing approx. 4000
  times the weight of the earth!
• (And a single bacterium weighs approx.
  one-trillionth of a gram)

• Why havent bacteria, then, grown to fill the
  entire earth? Why arent we knee deep in them?
• Answer eventually something _________ their
  __________.
• Such as?
• --lack of __________, build up of ___________,
  environmental conditions, predation, etc.

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The Bacterial Growth Curve
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_____ phase -- period after inoculation of a
culture before growth begins. Exponential phase
-- period of exponential growth _______________
phase -- period in which growth ceases Death
phase -- period in which cells die off
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Growth curve animations
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How do we measure growth?

• Total cells count (or direct microscopic counts
  or just _________ ___________)
• Viable counts (also called ___________
  ____________ or colony counts)
• Measurements of cell mass and _____________

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a.k.a direct counts, total cells counts
Text Fig. 7.16
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Viable count
Sample pipetted onto agar surface
Sample spread evenly over surface
Incubation
_______ plate method
Typical results
_________ plate method
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Viable counts using ___________ ___________
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Measurements of cell mass and turbidity

• 1. Measuring ________ __________ centrifuge
  organisms and _________ them (usually dried).
• Cell mass is proportional to cell number
• 2. Measuring ________________ measure
  cloudiness of a cell suspension by light
  scattering.
• Turbidity is proportional to cell number, also
  

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Measurement of turbidity using a
____________________
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Typical growth curve data (obtained in Klett
units) for two organisms growing at different
growth rates
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Cell number or dry weight and turbidity are
___________________

• In other words, once you know one, you can figure
  out the other if you know their relationship

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Chemostat -- a device for continuous culture
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Effect of environmental factors on microorganisms

• 1) Important to distinguish between effects on
  _____________ (whether the cells survive) and
  effects on ____________ (including reproduction).
• 2) Important factors
• _____________
• _____________
• _________ availability
• oxygen

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Effect of temperature on growth rate

• Each microorganism has a minimum, maximum, and
  ___________
• Organisms can be classified by temperature

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Effect of temperature on growth rate
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Boulder Spring, a boiling spring in Yellowstone
National Park
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Growth of thermophilic cyanobacteria in Grand
Prismatic Spring, Yellowstone
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Photomicrograph of a bacterial _________________
which developed on a microscope slide immersed in
a boiling spring
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RESEARCHERS DISCOVER EVIDENCE OF MICROSCOPIC
LIFE AT THE SOUTH POLE

• July 6, 2000
• In a finding that may extend the known limits
  of life on Earth, researchers have discovered
  evidence that microbes may be able to survive the
  heavy doses of ultraviolet radiation and the
  extreme cold and darkness of the South Pole.
• The team's findings, published in Applied and
  Environmental Microbiology, the journal of the
  American Society for Microbiology, indicate that
  a population of active bacteria, some of which
  have DNA sequences that align closely with
  species in the genus Deinococcus, exists at the
  South Pole in the austral summer. A similar
  species lives elsewhere in Antarctica, but the
  discovery of microbes at the Pole may mean that
  the bacteria have become uniquely adapted to the
  extreme conditions there, including a scarcity of
  liquid water.
• A species in the genus Deinococcus was first
  discovered in cans of irradiated meat in the
  1950's, and is able to withstand extreme dryness
  and large doses of radiation. It is possible
  that the related bacteria from the South Pole may
  also possess these characteristics.
• "While we expected to find some bacteria in
  the South Pole snow, we were surprised that they
  were metabolically active and synthesizing DNA
  and protein at local ambient temperatures of
  -12 to -17 Celsius (10.4 to 1.4 degrees
  Fahrenheit)," said Edward J. Carpenter, of the
  State University of New York at Stony Brook.

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Effects of pH
________________
Cytoplasmic pH
_______________
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Effects of salt (sodium ion concentration) on
_________ ___________ of various microorganisms
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Toxic forms of oxygen
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Enzymes acting on toxic oxygen species
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Method for testing a microbial culture for the
presence of ____________