When and why the antibiotics
are produced?
Bacterial growth curve
• Streptomycin production by Streptomyces
griseus and other microorganisms is divided
into 2 phases:
• 1- Prophase
• 2- Idiophase
• The Prophase is characterized by rapid
consumption of nutrients and growth, but low
rate of antibiotic production.
• During
Pophase,
mycelial
nitrogen,
phosphorous, SH groups and RNA reached
maximum levels and oxidation of glucose
through HMP pathway was rapid.
• During the second phase (Idiophase), the rate
of growth decreased and biosynthesis of
streptomycin increased.
• In the idiophase there are reduction in
nitrogen, phosphorous, SH groups,RNA
synthesis and oxidation of glucose is
minimum.
• The growth is measured by increase in DNA
replication whereas the end of replicating
growth phase is measured by:
a- drop in respiratory activity
b-decrease in RNA synthesis
These two states occur due to enzyme limited
and substrate limited conditions.
Primary and secondary metabolites in
relation to antibiotic production
• Primary metabolism: metabolic pathways that
provide energy and biosynthetic intermediates
that further converted to nucleic acids,
proteins, polysaccharides and lipids.
• Secondary metabolism: involved synthetic
process whose end products “ Secondary
metabolites” play no role in the economy of
the microorganism.
• Secondary metabolism begins when cells stop
growing for some reason and metabolic
intermediates or end products accumulate in
the cytoplasm.
• Secondary metabolites may be toxic to the
microrganism, so they are converted into inert
products which are non-toxic to the producer
organism but toxic to another microrganism
i.e: ANTIBIOTICS
Examples of antibiotics derived from
secondary metabolites
e.g: Penicillin is a combination of the amino
acids: L-valine + L- cystein+- amino adipic
acid.
Streptomycin is a combination of three
amino sugars
Ecological role of antibiotics
• Most antibiotic producing microbes are naturally
occurring in the soil.
• Production and secretion of antibiotics may give
their producers a selective advantage in the soil
environment:
- The antibiotic does not affect the producing
microbes.
- Secretion of the antibiotic may inhibit other
microbes which are competing for nutrients in
the same environmental nich.
ANTIBIOTICS HAVE PROTECTIVE ROLE ON THE
ORGANISM PRODUCING IT