growth of microbes-
TRANSCRIPT
Growth of Microbes-why should we know this?
• Control of growth is important for • infection control
• growth of industrial and biotech organisms
• Controlling food infections
Why Bacteria?
• Reproduce rapidly
• Can produce complex molecules (e.g.enzymes)
• Genetic code similar to us
• Presence of plasmids
• Less ethical concerns
Shapes of bacteria
Binary Fission
• Bacteria divide by Binary Fission.• This is a form of asexual reproduction.• Under ideal conditions it can take place every 20 minutes!• In this way huge numbers of bacteria can be produced very rapidly.
Generation Time• Time required for cell to divide/for population to double• Average for bacteria is 1-3 hours• E. coli generation time = 20 min
• 20 generations (7 hours), 1 cell becomes 1 million cells!
Bacterial Doubling Time
• Escherichia coli 20 minutes
• Mycobacterium tuberculosis 18 hours
• Mycobacterium leprae 14 days
Fig. 7.14a
Plotting growth on graphs
Factors Regulating Growth
• Nutrients
• Environmental conditions: temperature, pH, osmotic pressure
• Generation time
Environmental Factors Influencing Growth• Temperature
• O2
• pH
• Osmotic Pressure
• Others: radiation, atmospheric pressure
How to see their growth?Turbidity
Standard Growth Curve
Growth curve for Bacteria
Log
arit
hm
ic S
cale
Time
Lag phase Log Phase Stationary
Phase
Death Phase
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The Lag Phase
•After inoculation there is normally a brief
period of adaptation by the cells to the
new conditions.
•Bacteria are producing the enzymes
necessary to digest the nutrients.
•The rate of growth begins to increase
towards the end of this phase.
Return to graph
The Log (Logarithmic / Exponential)
phase
• There is a rapid period of growth during this
phase due to the fact that:
• Bacteria have developed the necessary
enzymes and there are plenty of nutrients.
• There are few waste products being
produced.
• The rate of cell division is currently at its
maximum with the number of bacteria
doubling as often as every 20 minutes.
Return to graph
The Stationary Phase
• The rate of growth levels off during this
period.
• This is because:
• The nutrients are becoming used up.
• The amount of waste produced by the bacteria themselves is increasing.
• The rate at which new cells are produced is equal to the rate at which other cells
are dying.
Return to graph
The Death (Decline) Phase
During this phase more bacteria are
dying than are being produced. This is
because:
• Very few nutrients are left.
• Many bacteria are poisoned by the
waste produced by such large numbers
•Thus the rate of growth is falling.
Return to graph
In unfavourable conditions many bacteria can
form endospores
These are highly resistant to drought high
temperature and other environmental
hazards.
Endospore Formation
Batch and Continuous Flow
food processing
A bioreactor is a vessel in which
biological reactions take place
Bio-processing (Food processing and Antibiotic
production)
• Modern bio-processing methods involve the use of bacteria and fungi to produce a wide range of products.
• These include dairy products e.g. yoghurts and cheeses, artificial sweeteners, flavourings, vitamins and alcohol products such as wines and beers, and antibiotics
There are two main methods of food processing:
• Batch food processing
• Continuous flow food processing
Batch processing
• In batch food processing a fixed amount of sterile nutrient is added to the micro-organisms in the bioreactor.
• The micro-organisms go through the stages of a typical growth curve
• i.e The Lag, Log, Stationary and Death stages
• The reaction may be stopped before the death stage as very little product will be formed at this stage.
• At the end of production the bioreactor is cleared out. The product is separated from the rest of the solution and is purified.
• The bioreactor is cleaned and re-sterilised.
• The process can then be repeated.
Time (days)
Lag phaseLog Phase Stationary
Phase
Death Phase
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In Batch Processing most of the product is formed during the
stages highlighted below
Nutrients and
micro-
organisms
added here
Gas out here
Oxygen (if required)
in here
Stirrer
Sparger
Bioreactor for Batch Food Processing
Product is released
at the end of the
process
E.g: Penicillin produced using batch fermentation in a bioreactor
(Penicillin is a secondary metabolite i.e it is produced when growth slows down)
Continuous flow food processing
• In continuous flow food processing nutrients are continuously fed into the bioreactor.
• At the same time the culture medium (containing some micro-organisms) is continually withdrawn.
• In this method of food processing micro-organisms are maintained in the Log phase of growth and the process can continue uninterrupted for weeks, even months.
• In continuous flow bioreactors factors such as temperature, pH, rate of stirring, concentration of nutrients, oxygen and waste products are constantly monitored in order to maintain growth in the Log phase and therefore produce the maximum yield.
Time (months)
Lag phase Log Phase
Nu
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acte
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In Continuous Flow Processing most of the product is formed
during the stage highlighted below
Nutrients fed in
continuously Gas out here
Oxygen
in here
Stirrer
Sparger
Product (and
culture medium)
flows out
continuously
Bioreactor for Continuous Flow Food
Processing
Product
Enzymes in food production
• Protease from bacteria softens gluten, making rolling of biscuit easier
• Pectinase breaks down clumps of plant cells, makes fruit juices from cloudy to clear
• Lipase and Proteases in biological washing powders can remove stain from fatty food/grease and from blood (working at low temperature, and clothes do not shrink)
• Lipase from fungi helps make chocolate flow to cover biscuits and sweets
• Lactose free milk using Lactase enzyme
Haber process of producing ammonia without using enzymes requires - 750 degrees C Temperature- - 30 times of atmospheric pressure
- Nitrogen fixing bacteria can perform this process at 25 degrees C and at atmospheric pressure because of enzymes it contains
- Majority of enzymes used commercially are obtained from microbes (usually fungi and bacteria). These microbes can be grown under carefully controlled conditions in a bioreactor (=fermentor)
Video on Enzymes
Enzymes – speed up biological reactions