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Commercial biotechnology
Learning objectives:
• To be able to explain the advantage of
using microorganisms for industrial
processes.
• To be able to describe the screening
procedures carried out to identify the
most suitable microorganisms for a
particular process.
Microbes are particularly useful for
industrial purposes because
• They have fast growth rates.
• They have simple nutritional requirements and can
often be fed on cheap or even waste substrates such
as molasses, whey, wood pulp, etc.
• They can be grown indoors and their growth does not
depend on seasons, climate, latitude, etc.
• They are often tolerant of a wide range of
temperatures and pH.
• There are fewer ethical problems, when compared to
animals.
• Prokaryotes can be more easily genetically modified
than eukaryotic cells, since they don't have a
nucleus. Genes from other species can easily be
inserted into the bacterial DNA to produce a range of
gene products by fermentation, or the microbe can
be altered to produce far more of the product than
normal.
Screening
• This is selecting a suitable species and
strain of bacteria for a particular job.
• This involves testing every bacterium
you can find to see if it makes the
product you want in the right quantities
and at the right speed.
• This can account for most of the cost
of development as it can take years.
Extracellular enzymes (ones that are
secreted by the microorganism) have three
main advantages over those that are
intracellular:
a. The enzyme is already outside the cell, so
the cells do not need to be broken open.
b. Only a limited number of enzymes are
secreted, so isolation is much easier.
c. Extracellular enzymes are less likely to be
broken down by heat/chemicals (more
robust).
Screening can be used to detect the
presence of extracellular enzymes:
a. Amylases are detected by plating on
agar containing starch. After incubating,
iodine is added, so that the microbes
that break down the starch have clear
zones around them.
b. Proteases are detected by plating on
agar containing casein (makes the
plates look cloudy). The microbes that
break down the casein have clear
zones surrounding them.
Antibiotic production can be detected by
plating the microbes with a test
organism such as Staphylococcus
aureus. The presence of areas in which
the test organism doesn’t grow
indicates the presence of antibiotics.
Substances produced by microorganisms are
classified into two groups:
• Primary metabolites – produced during the
growth of the organism (normal growth
products). These include amino acids,
nucleotides, acids, ethanol and enzymes:
– i. Acetobacter sp. – production of ethanoic
acid.
– ii. Aspergillus niger – production of
pectinases.
– iii. Bacillus subtilis – production of
proteases (tenderising meat).
• Secondary metabolites – chemicals that are
not directly involved in normal growth, e.g.
antibiotics. These are produced after the
main growth period is completed or under
extreme or unusual conditions
• Microorganisms make some enzymes
continually, whilst others maybe made
only when needed
• For example, some microorganisms
may only make a particular antibiotic or
enzymes in overcrowded conditions to
kill competing microbes.
• Primary and secondary metabolites
must be harvested at different stages of
cell growth, so it is important to be able
to make a distinction between them
In order to maximise production of a
particular metabolite, different methods
are used:
The first method is Continuous Process:
– the nutrients are continually inputted
into the fermentation vessel, and the
material is continually removed and
processed.
– This may be more economical, as it
doesn’t have to be shut down on a
regular basis.
• This method maximises primary
metabolite production as the microbes
are keep in the exponential phase.
Continuous Fermenters
• This takes place in an open or flow-through
fermenter.
• The culture is continuously run off to make
the product, while nutrients are continuously
added at the same rate.
• The rate is set to match the growth rate so
the number of cells in the fermenter stays
constant.
• This is very efficient, since the microbesbare
kept at their exponential growth phase.
Batch process –
– raw materials and microbes are
placed together in a container vessel.
– The microbes are then allowed to
grow to their maximum population
size, then the fermenter is emptied
and the products are extracted and
purified.
• This method maximises secondary
metabolite production as the microbes
are allowed to enter the stationary
phase
Batch Fermenters
• The fermenter is sterilised using high pressure
steam to kill any other microbes that may infect the
batch.
• In batch fermentation the cells show a typical growth
curve pattern. If left long enough the nutrients will be
used up and the cells will die.
• This would be waste time and so products are
drained off at the end of the stationary phase.
• Once the product has reached its maximum
concentration, the fermentation is stopped and the
medium is run off.
• The fermenter is sterilised and a new batch is
started.
Advantages and disadvantages:
CONTINUOUS
• Faster production rate
• Automated so cheaper
to run
• Less labour intensive
due to automation
• More continuity of
product
• Continuous supply
• Can use smaller vessel
• Difficult to get right
• Fermenter only suitable
for one process
• High initial cost of
complex equipment
• Hard to achieve
constant sterility
• If contaminated more is
lost/wasted
Advantages and disadvantages:
BATCH
• Simple to set up
• Only one batch lost if
contaminated
• Can be sterilised
between batches
• For fed batch process
nutrients can be added
at intervals to prolong
the stationary phase
• Fermenters are versatile
and can be used for
many processes
• Time lost between batches
• Time to get going – lag
phase – slow production
• Need to maintain
consistency
• Need to be sterilised
• Nutrient wasted if not all
used up
• Amount of product limited
by initial amount
• Labour intensive due to
start/stop cycle
• Large vessels needed to be
cost effective
Fermenter requirements:
• Strong
• Smooth
• Non corrosive
• Easily sterilised (metal)
• Non reactive
Fermentation may be:
• Surface or submerged
• Aerobic or anaerobic