Prof. Robert Gunsalus
office hours, 10-11 MWF
3610C Mol. Sci. Bld.
Prof. Peter Bradley
office hours, Mon 4-5, Fri 3-4
2610B Mol. Sci. Bld.
Today:
Cell Growth & Effect of Environmental Factors
Brock, chapter 6 & p 103-110
Friday
The Cell Envelope & Cell Surface Structures
Brock, p 64-81, 389-390
Today’s Overview:
1. How cells grow in continuous culture.
2. Effect of environmental factors on cell growth.
Batch cell culture
Growth of Microorganisms
Batch cell culture
vs
Continuous cell culture
Characteristics of cell growth in Batch Culture:
The system is "closed"
no addition of new material
no removal of waste material
no removal of cells
The cell density increases until….
….something becomes limiting!
A typical batch culture growth curve
cell density increases at the maximum rate!
Cell growth in Continuous Culture
“Continuous Culture” - system is "open"
- continual addition of nutrients
- continual removal of cells
- continual removal of waste materials
As a result, cell density remains constant!
Examples of microbial growth in Nature
in Continuous Culture
- bacteria in a stream or river
- bacteria in human intestines
- stomachs of cows, goats, horse, etc.
How to do this in the laboratory?
A
chemostat
device
Rate of inflow is equal to the rate of outflow!
the medium addition rate = vessel dilution rate
Thus…under nutrient limiting conditions, the
rate of nutrient addition controls the cell growth rate!
Cells are growing slower because they
lack sufficient carbon or some other
essential nutrient they need to grow fast!
And….under nutrient excess conditions, the
rate of nutrient addition controls the cell yield
(i.e., number of cells per ml.)!
Addition rate
Cell dt
(doubling time)
1000 ml/hr
2000
3000
500
200
100
1 per hr
2 per hr
3 per hr
0.5 ( 2 hrs)
0.2 ( 5 hrs)
0.1 (10 hrs)
Dilution rate controls growth rate!
1000 ml
volume
Batch Culture
vs
Continuous Culture
system is "closed"
system is "open"
no addition of materials
constant additions
no removal of materials
constant removal
cell growth rate is maximum
cell growth is limited
cell density changes
once at equilibrium, cell
density remains constant!
nutrients are depleted
nutrient levels stay constant
waste products accumulate
waste products are constant
How can a chemostat be used experimentally?
number of ribosomes in batch culture?
are maximized for protein synthesis in exponential phase
For E. coli growing in a
Chemostat at different rates
# of
ribosomes
per cell
20000
15000
10000
5000
0
0.5
1
1.5
2
Cell doublings per hour
Conditions for Cell Growth
Effect of environmental
conditions on cell growth
Temperature
pH
Oxygen
Osmolarity
What is the permissible
temperature range
for cell growth?
Consider E. coli cells
We can determine this
Experimentally..
37 C
25 C
1. Grow cultures at
different temperatures
2. Calculate growth rates
3. Plot vs temperature
10o
37o
42o
Algal growth in snow
-5o
15o
20o
Ice core
Brock figure 6.18
p. 153
photosynthetic microbes
Arial photograph of a large boiling spring in Yellowstone Park
Effect of environmental
conditions on cell growth
Temperature
pH
Osmolarity
Oxygen
Microbial growth of E. coli at pH 7.0
pH 2
Acidophiles
pH 7
pH 11
Neutral
Alkaliphiles
A Unifying Feature of Bacteria:
- the internal cytoplasmic pH is always about 7.0
- acidophiles and alkaliphiles have strategies
to maintain internal cell pH.
- counter balance entry of protons by
proton pumping and by uptake of K +
- buffer ability can also be controlled by
synthesis of glutamate or polyamines.
.
Effect of environmental
conditions on cell growth
Temperature
pH
Osmolarity
Oxygen
Know these terms:
aerobes - anaerobes - facultative - microaerobes - aerotolerant
The End