Strain improvement part I, Types of control mechanism in micro-organisms

STRAIN IMPROVEMENT
Part I
Types of Control in
Microorganisms
Mentor: Ms. Renu NK Jaisinghani Prepared By : Ms.Priyanka Kadam
Assistant Professor
Department of Microbiology
Smt. CHM College

DEFINITION OF STRAIN IMPROVEMENT:
It is a process of modifying genotype of organism so
as to make it a better industrial strain than existing
one with respect to yield or any other property that
makes the process economic and simple.

MUTATION: Isolation of induced mutants using
Physical (uv , X rays , gamma rays ,etc.) or Chemical
(NTG, alkylating agents, 2 amino purine ).
RECOMBINATION: By selecting new recombinants
by using recombination technique like sexual
recombination, parasexual cycle, transformation,
conjugation transduction, lysogeny, phage
conversion, spheroplast / protoplast fusion.

PRINCIPLE:
Underlying strain improvement method is to
modify genotype of natural industrially important
isolate by mutation or recombination so as to
make it much better industrial strain that is high
yielding, more suitable for fermentation process
and makes the process economic.

SIGNIFICANCE/ IMPORTANCE/ ADVANTAGES
OF STRAIN IMPROVEMENT:
1. It helps in obtaining higher yielding strain,
2. It helps in obtaining more stable strain.
3. It helps in obtaining strain that makes the process
economic.
4. Helps in selecting strain with better properties like
resistance to phage , non-foaming, requiring low oxygen
tension, not producing undesirable by-product , etc.

Before studying methods of selecting strain giving higher
yield it is necessary to study mechanism of control of their
biosynthesis to construct “ blue prints” of useful
organisms.
Two main systems involved in regulation of production of
primary metabolites:
FBI [Feed back Inhibition]
FBR [ Feed Back
Repression]

FEED BACK INHIBITION [FBI]- Is the situation
where product of a biochemical pathway inhibits the
activity of enzyme catalyzing one of reactions of the
pathway ( normally the 1st reaction).
Inhibition occurs because products bind with enzyme.
Catalyzing reaction may / may not be at allosteric site
and interfere with binding of enzyme with substrate
and thus stops further synthesis of product.

FEED BACK REPRESSION[FBR]: is the situation
where end product of biochemical pathway
prevents the synthesis of enzyme/enzymes
catalyzing the reaction / reactions of the pathway.
Inhibition occurs at gene level as product prevents
the transcription of gene (coding for enzyme) in
mRNA and thereby its synthesis.

Such regulation systems (FBI and FBR) plays important role in
organism and helps in avoiding wastage of ‘E’ in over synthesis
of any product.
Micro organism will always synthesize any product in amount
just enough for their survival and growth.
The control of biosynthetic pathway giving no. of end products (
branched pathway)is more complex than simple unbranched
pathway.
The end products of same branched biosynthetic pathway are
rarely required by micro-organisms to the same extent,
therefore if an end product exerts control over a part of
pathway common to two or more end products then organisms
may suffer deprivation of products not participating in the
control.
Thus regulation mechanism in an organism is such that synthesis
of end products of branched pathway is controlled without
depriving the cell of essential intermediates.

There are 5 main types of regulation systems studied in
organism that control branched pathways of biosynthesis
CONCERTED FEED
BACK CONTROL
CO OPERATIVE
FEED BACK
CONTROL
CUMULATIVE FEED
BACK CONTROL
SEQUENTIAL FEED
BACK CONTROL
ISOENZYME FEED
BACK CONTROL

1. CONCERTED FEED BACK CONTROL:
It involves the control of pathway by more than one
end product i.e enzyme of pathway is inhibited only
when all the end products of the pathway are in excess.

2.COOPERATIVE FEED BACK CONTROL:
The presence of all the end products in excess results in a
synergistic inhibition by inhibiting 1st enzyme of the pathway but
weak control may be exerted by each product independently .
When any one product is in excess , it can exert weak inhibition
just after the branched point leading to the excess of product and
thus flow of intermediate product will be diverted to the product
which is still required.

3. CUMULATIVE FEED BACK CONTROL:
Each end product of pathway exerts inhibition of 1st
enzyme by 50% independent of other end products ;
total inhibition occurs when both the products of
pathway are in excess.
Also each end product can exert complete inhibition just
after the branched point.

4.SEQUENTIAL FEED BACK CONTROL:
Each end product of the pathway controls the enzyme after
the branched point to the product.
The intermediate product then accumulates and can inhibit
its own synthesis.

5.ISOENZYME FEED BACK CONTROL:
Let E1 and E2 be the two isoenzymes [enzymes having
different form but catalysing same reaction].
In such case different isoenzymes may be controlled by
different end products.

Reference
• Stanbury, P.F., Whitaker, A. Principles of
Fermentation Technology 2E.

Strain improvement part I, Types of control mechanism in micro-organisms

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