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INFLUENCING THE GROWTH OF
Dr. Ruchi Seth
Assistant Professor - I
Department of Biotechnology
Presented By :
An orderly increase in the quantity of all the cellular
The growth of microorganisms is influenced by
various physical and chemical factors of their
Physical factors- Temperature, pH, osmotic
pressure, hydrostatic pressure and radiation.
Chemical factors- Oxygen, carbon, nitrogen,
phosphorus, sulfur, etc.
Temperature is the most important factor that
determines the rate of growth, multiplication,
survival, and death of all living organisms.
High temperatures damage microbes by
denaturing enzymes, transport carriers, and other
Microbial membrane are disrupted by
At very low temperatures membranes also solidify
and enzymes also do not function properly.
Types of temperature
Minimum growth temperature
Optimum growth temperature
Maximum growth temperature
1. Minimum growth temperature
The lowest temperature at which organisms grow is
the minimum growth temperature.
2. Optimum growth temperature
The temperature at which the most rapid rate of
3. Maximum growth temperature
The highest temperature at which growth occurs.
A temperature only slightly above this point
frequently kills the microorganisms by inactivating
Classification of bacteria according to
1. The term psychrophile was first used by S.
2. Extremophilic organisms that are capable
of growth and reproduction in cold temperatures
3. Temperature range: −20°C to +10°C.
4. Examples: Oscillatoria, Chlamydomonas nivalis,
1. Grows best in moderate temperature.
2. Temperature range: 20°C to 45°C.
3. Examples: Escherichia coli, Streptococcus
1. Cold‐tolerant bacteria.
2. Have optimal and maximal growth temperatures
above 15 and 20°C, respectively.
3. Psychrotrophic bacteria and fungi are the
principal cause of spoilage of refrigerated food.
4. Examples: Pseudomonas, Aeromonas,
Bacillus, Clostridium, etc.
1. Derived from Greek word thermotita meaning
heat and philia meaning love.
2. Heat-loving microorganisms.
3. Grow at 50°C or higher. Their growth minimum
is usually around 45°C and often optima
between 50 and 80°C.
4. Examples: Thermus aquaticus, Geogemma
1. Thrives in extremely hot environments.
2. Temperature range: 80°C to 113°C.
3. First discovered by Thomas D. Brock in 1965 , in hot
springs inYellowstone National Park, Wyoming.
4. The cell membrane contains high levels of saturated
fatty acids to retain its shape at high temperatures
5. Examples: Sulfolobus, Methanococcus jannaschii,
pH refers to negative logarithm of hydrogen ion
Microbial growth is strongly affected by the pH of the
Drastic variations in cytoplasmic pH disrupt the
plasma membrane or inhibit the activity of enzymes
and membrane transport proteins.
Classification of bacteria according to pH
Acidophiles- Grow between pH 0 and 5.5.
Examples: Ferroplasma, Thiobacillus thioxidans, Sulfolobus
Alkalophiles- Grow between pH range of 7.5 to 14.
Examples:Thermococcus alcaliphilus, etc.
Neutrophiles- Grow between pH 5.5 to 8.0
Examples: Lactobacillus acidophillus, E. coli,
Pseudomonas aerunginosa, etc.
Bacteria prefer media of pH near neutrality, and usually
cannot tolerate pH values much below 4-5.
Osmotic pressure is the minimum pressure which
needs to be applied to a solution to prevent the inward
flow of water across a SPM.
Types of solution:
1. Hypotonic 2. Isotonic 3. Hypertonic
Water activity of a solution is 1/100 the relative
humidity of the solution. It is equivalent to the ratio of
the vapour pressure of solution to that of pure water.
Vapour pressure of solution
Vapour pressure of pure water
Classification of bacteria according
to osmotic pressure
1. Osmotolerant are those microorganisms which can
grow at relatively high salt concentration.
Examples: Aeromonas spp., Staphylococcus spp, etc.
2. Halophiles- Grow in the presence of salt at conc.
Above 0.2 to 0.6.
Examples: Halobacterium halobium
Force acting per unit area.
Classification of bacteria on the basis
of hydrostatic pressure
Barotolerant – Does not get affected by
Barophiles/ Piezophiles- Bacteria which grow
at moderately high hydrostatic pressures.
salaria, xenophyophores, etc.
Sunlight-The major source.
Infrared is the major source of Earth’s heat.
Ionising rays can produce mutations which may
result in death.
Visible light is beneficial because it is the source
of energy for photosynthesis.
Microbiology, P.D. Sharma
General Microbiology, C.P Powar