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BACTERIAL GROWTH
CHARACTERISTICS
Dr. Muhammad Khurram,
B. Pharm., Ph. D.

Growth and Genetic Exchange
 Primarily it’s the Binary fission
 But bacteria has the ability to exchange and
share the DNA that helps them to adapt rapidly
to the changes in their environment
 Three major processes of genetic exchange
are
1. Transformation
2. Transduction
3. Conjugation

Transformation
 It is the process of transferring free DNA
released from a donor bacterium into the
extracellular environment that results in
assimilation and usually an expression of the
newly acquired trait in a recipient bacterium.
 Its of Two types:
1) Natural transformation occurs when some
bacterial genera spontaneously release DNA from
the cells into the environment free to be taken up
by the competent cells.
2) Artificial transformation, is the transfer of
artificially altered DNA into recipient cells

Transduction
 Bacterial transduction is a process of transferring
bacterial DNA from a donor to a recipient bacterium
via a virus particle called a bacteriophage or phage
 Its also of two types
1. Generalized transduction occurs when phages
mistakenly package bacterial DNA instead of their own
DNA during phage assembly. This results in an infectious
virus particle containing bacterial DNA
2. Specialized transduction, on the other hand, occurs
when a temperate phage integrates its DNA into the
bacterial chromosome and then excises itself along with
some flanking bacterial DNA. The phage DNA is then
packaged into a phage particle and transferred to a new
host bacterium

Conjugation
 Bacterial conjugation is a process by which
genetic material is transferred between
bacterial cells through direct cell-to-cell contact
or a bridge-like connection between two cells.
 This process is facilitated by a pilus, which is a
long and robust extracellular appendage that
serves as a physical channel for translocation
of DNA that is most often a plasmid or
transposon.

Growth Rate..
 Parameters
placed on X-axis
 Growth is kept
on Y-axis
 Relationship is
studied
Optimum
X-axis
Y-axis
0

Nutrients for Growth!
 Nutrients are substances used in
biosynthesis and energy release
and therefore are required for
microbial growth.

Macronutrients..
 Over 95% of cell dry weight is made up
of a few major elements: Carbon,
Oxygen, Hydrogen, Nitrogen, Sulfur,
Phosphorus, Potassium, Calcium,
Magnesium, and Iron. These are called
Macroelements or Macronutrients
because they are required by
microorganisms in relatively large
amounts. The first six (C, O, H, N, S,
and P) are components of
carbohydrates, Lipids, Proteins, and

 The remaining four macroelements exist in the cell
as cations and play a variety of roles. For example,
Potassium (K+) is required for activity by a number
of enzymes, including some of those involved in
protein synthesis. Calcium (Ca+2), among other
functions, contributes to the heat resistance of
bacterial endospores. Magnesium (Mg+2) serves
as a cofactor for many enzymes, complexes with
ATP, and stabilizes ribosomes and cell
membranes. Iron (Fe+2 and Fe+3) is a part of
cytochromes and a cofactor for enzymes and
electron-carrying proteins.

Micronutrients…
 All microorganisms require several
nutrients in small amounts. These are
called micronutrients or trace elements.
The micronutrients— Manganese, Zinc,
Cobalt, Molybdenum, Nickel, and
Copper—are needed by most cells.
 Micronutrients are normally a part of
enzymes and cofactors, and they aid in the
catalysis of reactions and maintenance of
protein structure.
 Naturally present in media, water, etc.

Growth factors..
 Organic compounds that are essential cell
components or precursors of such components
but cannot be synthesized by the organism are
called growth factors.
 There are three major classes of growth factors:
(1) Amino acids,
(2) Purines and Pyrimidines,
(3) Vitamins.
 Amino acids are needed for protein synthesis;
purines and pyrimidines for nucleic acid synthesis.
 Vitamins are small organic molecules that usually
make up all or part of enzyme cofactors and are

Physicochemical factors impact
 The physicochemical factors that affect the
growth and survival of bacteria
 Temperature
 pH
 Water activity / Solutes
 Availability of Oxygen
 Pressure
 Radiation

Effect of Temperature..
 Cardinal
temperatures

bacterial growth charactrstics.pptx Mbbs

Effect of pH..
 Optimum pH
 Metabolic activities

Water activity / Solutes…
 Water activity (aw)
 Availability of water OR The ratio of vapor
pressure of the air in equilibrium with a
substance or solution to the vapor pressure of
pure water.
 Osmosis: Water flow from its higher
concentration to lower concentration
 Compatible solutes: The solute used inside
the cell for adjustment of cytoplasmic water
activity that are non-inhibitory to
macromolecules within the cell. E.g. Sugars,
Alcohols, Amino acid derivatives

Effect of O2..
1) Aerobes
2) Anaerobes
3) Facultative
aerobes
4) Microaerophiles
5) Aerotolerant
 Capnophiles..

Biofilms
 Microbes in aquatic environments were found
attached to surfaces (sessile) rather than were
free-floating (planktonic)
 These attached microbes are members of
complex, slime-encased communities called
biofilms
 Major concern is the formation of biofilms on
medical devices such as hip and knee
implants.
 These biofilms often cause serious illness and
failure of the medical device.

 Biofilm coated on
artificial knee joint

Measuring the Growth
 Direct Microscopy

 Viable count
using serial
dilutions and
pour-plate
method

Turbidimetric
methods
 Optical Density at
a particular 

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