3. Investigating metabolism in microorganisms

Investigating metabolism in microorganisms
Environmental control of metabolism
(iii) Controlling metabolism
Links to prior/prerequisite knowledge
Unit 2: Metabolism and Survival (1a and 1b)
New content areas
 The definition of primary/secondary metabolites.
 Use of inducers or inhibitors to control metabolism in order to produce a
particular metabolite.
Background information
 Industrial microbiology originated with alcoholic fermentation processes
such as those used to make beer and wine. Subseque ntly, processes were
developed for the production of antibiotics, food additives, enzymes and
useful chemicals. All of these industrial processes are enhancements of the
metabolic reactions that microorganisms were already capable of carrying
out. Specific growth conditions, inducers or inhibitors are employed to
modify natural metabolic pathways to ensure the highest possible yield of
product is obtained.
 Many biotechnology products are made by growing microorganisms in
fermenters or bioreactors, for example penicillin (an antibiotic) and beer
are produced in large quantities in fermenters containing as much as
100,000 litres of culture medium.
 In this section we consider the microbial growth process as it occurs in an
industrial process in which a microbial metabolite is the desired product.
There are two basic types of microbial metabolites :
- primary: product is formed during the primary growth phase, for
example ethanol production
- secondary: product is formed during the stationary phase. Many
economically valuable microbial products are secondary metabolites
such as penicillin. The rest of this background information will focus on
secondary metabolites.
 Secondary metabolites are seemingly not essential for growth and
reproduction. Their formation is extremely dependent on growth
conditions, especially on the composition of the medium. Since many
enzymes may be involved in the production of secondary metabolites,
specific inducers or inhibitors may have to be identified to ensure
production of the required enzymes.
- Example for the effect of growth conditions: Citric acid is used
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widely in foods and beverages. It is produced industrially by
Aspergillus niger. Production is carried out aerobically in large
fermentors and a key requirement for high yield is th at the growth
medium be iron deficient.
- Example of an inducer: The antibiotic streptomycin is synthesised as a
typical secondary metabolite. Its production is regulated by the use of
an inducer called factor A. Key enzymes in streptomycin production are
not synthesised until factor A concentration builds up. When factor A
reaches a critical level in the growth medium, it induces synthesis of
streptomycin biosynthesis enzymes.
Identification of key concepts
Some fermentations may require the addition of me tabolic precursors,
inducers or inhibitors to control metabolism to give the required
Secondary metabolism produces substances not associated with
growth, which may confer an ecological advantage (antibiotics,
insulin, citric acid etc).
Identification of particular areas of difficulty
Links to websites, animations, PowerPoints, audio or video files etc
Other useful information to stimulate interest
© Learning and Teaching Scotland 2011