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Microbial Growth Chapter 6
(6.16.16)
(In microbiology growth is defined as an increase in cell number:
“The bacterial population is
growing
in number.”)
Cell division in prokaryotes
Called _Binary Fission
____
See figure 6.1 for steps
Note that cell division in prokaryotes is much simpler than in eukaryotes.
Cell division in
eukaryotes (mitosis) must also involve accurate division of all the separate chromosomes.
Fts Proteins and Cell Division
Series of proteins found in prokaryotes that interact to form divisome
Some of these proteins include:
FtsZ:
(first step) forms a ring in the middle of a cell (once DNA replication is
over)
FtsA:
hydrolyzes ATP for energy
FtsI:
involved in new peptidoglycan synthesis
FtsK: involved in pulling apart DNA molecules
Figure 6.2a
Arrangement of divisome proteins
How are cell shapes determined?
NOT by arrangement of peptidoglycan
MreB protein
Forms actinlike filament
Different arrangements = different shapes
Coccusshaped bacteria lack gene for MreB
Spherical is “default”
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View Full Document Peptidoglycan Synthesis and Cell Division
Openings in existing wall created at FtsZ ring by autolysins
Precursors transported by bactopreno
l
Transpeptidation
Formation of peptide bond crosslinks
Target of penicillin
Population growth
“population” because we refer to the growth of a population of microorganisms, not the growth
of a single organism
Some definitions:
Growth rate: change in cell number per unit time
Generation time: time required for one round of cell division (a
generation), doubling time (depends on species/genetics and
environment)
 Prokaryotes typically faster than eukaryotes
Exponential growth – total cell number of population doubles each unit
time
See figure 6.6a for an example of exponential growth.
Note that the number of
cells in the population is doubling every 30 minutes.
The growth rate
continuously increases in exponential growth.
For example, in the 30 minute
span from 1 to 1.5 hours the cell population increased by 4.
In the 30 minute
span from 5 to 5.5 hours, the population increased by 1,024.
Also see figure 6.7b for a plot of exponential growth.
Note that from this graph
you can determine the generation time (time it takes to double).
The cell number
doubles when it changes from 3 x 10
7
to 6 x 10
7
.
How much time did it take for
the culture to go from 3 x 10
7
cells/ml to 6 x 10
7
?
That is the doubling time.
Calculations of growth
N=N
o
2
n
g=t/n
N= final number
N
o
= initial number
n= number of generations
t= hours or minutes of exponential
growth
g= generation time
Sample problem:
Escherichia coli
has a generation time of 20 minutes, it has been growing exponentially
for 3 hours, and this culture was initially started with 5
E. coli
cells.
How many generations have occurred in the 3 hours?
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This note was uploaded on 10/01/2008 for the course BIOL 2051 taught by Professor Brininstool during the Fall '07 term at LSU.
 Fall '07
 Brininstool
 Microbiology, Bacteria, Binary Fission

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