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Prokaryotic Growth
I. What is growth?
A. Population growth:
B. Cellular growth:
C. What happens during growth?
D. Generally cells make all their constituents until they have
twice as much and then they divide.
II. How do prokaryotes grow?
A. By a process called ____________ fission.
B. The time required for a population of cells to double is:
C. E. coli doubles every 20 min. Some take days to double.
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III. Population growth can be quantified because:
A. Population growth is _____________________.
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1 cell >> 2 cells >> 4 cells >> 8 cells >> etc.
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On a logarithmic scale cells # follows a
_______________ line.
IV.
Population growth can be studied through growth curve analysis:
A.
One way to do this is by growing cells in a a closed system:
which is called ______________ culture.
This is done by:
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V.
The growth phases in closed system:
A.
Lag Phase:
B.
Exponential phase:
C.
Stationary phase:
D.
Death phase:
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VI. Growth curve analysis is a classic approach to investigating
physiological response of strains to a particular culture
condition:
A. Example: determine temperature optimum of a new strain.
VII. Here is how to quantify certain parameters of a growth curve:
A. There is a direct relation between number of cells
initially, and number of cells after a period of exponential
growth.
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N=N02n
(N=final cell number, N0= initial cell number, n=
number of generations or doublings)
Example: You start out with 50 cells, and you want
to end up with about 50,000.
How many doubling times should you allow?
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VIII.Calculating generation time g (doubling time):
A. Calculation is only done in the exponential part of the
growth curve.
B. From the previous example, if it took 3 hours to grow
from 50 cells to 50,000 what would be the doubling time
or generation time?
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Enumerating Prokaryotic Growth
What are common ways that microbiologists measure growth?
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Total Cell Counts:
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Use a microscope to obtain the cell counts
Calculate a cell density
Some problems with the method:
can’t count dilute samples
cells might be too small to count
cells might swim around
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Viable Count:
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If you are interested in only the living bacteria, viable
counts would be useful
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Viable =
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To determine the viable cell count:
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Often called:
The bacterium that made a colony is referred to as:
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If samples are to concentrated with bacteria what can you
do?
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E. coli can get up to 3-5 x 109 cells/ml
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0.1 ml is usually used for spread plating.
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That is 108 cells! That’s too much, will form a lawn
of cells.
The solution is:
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Example:
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Indirect measurement of cell numbers using absorbance:
1) Rapid method for estimating cell numbers.
2) Bacterial suspensions look cloudy.
3) Shine a light through and it scatters due to the turbidity of
the culture.
4) The spectrophotometer generates an optical density
number.
5) 540, 600, 660 nm are typical wavelengths use for the OD
measurements.
Spectrophotometer
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OD measurement vs.microbial growth
A. When you monitor growth vs. time:
B. The data can be used to:
C. Good value to compare physiological characteristics of two
strains.
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Pluses and minuses of various enumeration methods.
Enumeration
method
Direct counts
Viable counts
Indirect counts
Pluses
Minuses