7. Growing Bacteria
It needs to be the right temperature
this is usually 25-45℃
The bacteria will need some nutrients
agar is often used in the lab
Everything needs to be at the right pH
this is about 7.4 (slightly alkaline) for most bacteria, but most fungi like it more acidic
There needs to be enough oxygen, but not too much
different bacteria require different amounts of oxygen
•Obligate aerobes only live where there is oxygen
•Facultative aerobes don’t mind either way, but grow better with oxygen
•Obligate anaerobes can not grow in the presence of oxygen, like Clostridium,
which cause gangrene
8. Bacteria Life Cycle
Time
PopulationSize
1 2 3 4 5
Lag
Little growth, cells take
up water, carry out
protein synthesis and
produce enzymes
Log
Rapid (exponential)
increase in population
size
Death
More cells die than are
produced
Stationary
Cells die at a similar
rate as they are
produced
9. Working Safely
Prevent contamination from the environment
by sterilising everything before starting and handle everything carefully using appropriate
equipment
Handle everything correctly
by flaming the mouth of the bottle, passing the innoculating loop through the flame, only
lifting the lid of the petri dish just enough, taping the lid to the petri dish in two places
Sterilise all equipment in an autoclave
this is a sealed container which is heated to 121℃ at a high pressure for 15 minutes, which
ensures all pathogens are destroyed. Commercially, radiation works just as well.
Prevent contamination to the environment
by sterilising the working area before and after working with disinfectant
10. Recording Growth
Total Count
Count every single cell, living or dead
Viable Count
Count the living cells only
Serial Dilution
10cm3, which
contains
4000 cells, in
a test tube
9cm3 distilled
water, and 1cm3
from the last test
tube, so there’s
400 cells
9cm3 distilled
water, and 1cm3
from the last test
tube, so now
there’s 40 cells
1cm from
the last
test tube
gives
four
colonies
Haemocytometer
A microscope slide that allows you to count red
blood cells. It’s only useful for giving a total
count.
Turbidimetry
A specialised colorimeter measures the turbidity
(cloudiness) of a mixture which lowers as the
size of a population increases
12. Fermenter Design
Culture
The fermenter requires
a pure culture , this
eliminates competition
giving maximum
efficiency
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Sterile
The fermenter vessel
should be sterile and
protected by filters
from potential
contamination
Aeration
The mixing device, and
sterile air moving in
increases aeration for
growth and improves
the contact with
nutrients
pH Control
It may be necessary to
control the acidity of
the mixture slightly to
maintain the optimum
pH for growth
Temperature
Control
The cooling jacket, and
cooling water and a
thermostatically
controlled system
provide the optimum
temperature for growth
13. Penicillin Production
Next
After 30 hours,
production begins.
Penicillin is secreted by
the fungus, but only
after the exponential
phase has ended, when
glucose is depleted.
This means it is a
secondary metabolite.
First
The Penicillium
notatum is added to the
fermenter and beings
to grow in optimum
conditions
Time
PopulationSize
1 2 3 4 5
