This document discusses the physical factors that influence the growth of microorganisms, including temperature, pH, osmotic pressure, hydrostatic pressure, and radiation. It describes how each factor affects microbial growth and membranes. Temperature is the most important physical factor, as it can damage enzymes and membranes at extremes. Microbes are classified based on their optimal temperature ranges, such as psychrophiles, mesophiles, thermophiles, and hyperthermophiles. Optimal pH and osmotic pressure ranges also determine bacterial classifications like acidophiles, alkalophiles, halophiles, and osmotolerant microbes. Higher hydrostatic pressures and radiation can also impact microbial growth.

1. PHYSICAL FACTORS
INFLUENCING THE GROWTH OF
MICROORGANISMS
Guided by:
Dr. Ruchi Seth
Assistant Professor - I
Department of Biotechnology
Presented By :
Prachi Gupta
B.Sc. Biotechnology
I-Semester

2. Growth
 An orderly increase in the quantity of all the cellular
constituents.
 The growth of microorganisms is influenced by
various physical and chemical factors of their
environment.
 Physical factors- Temperature, pH, osmotic
pressure, hydrostatic pressure and radiation.
 Chemical factors- Oxygen, carbon, nitrogen,
phosphorus, sulfur, etc.

3. Physicalfactorsinfluencingthegrowthofmicroorganisms
Temperature pH
Osmotic
Pressure
Hydrostatic
Pressure
Radiation

4. Temperature
 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
proteins.
 Microbial membrane are disrupted by
temperature extremes.
 At very low temperatures membranes also solidify
and enzymes also do not function properly.

5. Types of temperature
Minimum growth temperature
Optimum growth temperature
Maximum growth temperature

6. 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
multiplication occurs.
3. Maximum growth temperature
The highest temperature at which growth occurs.
A temperature only slightly above this point
frequently kills the microorganisms by inactivating
critical enzymes.

7. Classification of bacteria according to
growth temperature

8.  Psychrophiles/cryophiles-
1. The term psychrophile was first used by S.
Schmidt-Nelson.
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,
Methanogenium, etc.

9.  Mesophiles-
1. Grows best in moderate temperature.
2. Temperature range: 20°C to 45°C.
3. Examples: Escherichia coli, Streptococcus
pneumoniae, etc.

10.  Psychrotrophs-
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.

11.  Thermophiles-
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
barossii, etc.

12.  Hyperthermophiles-
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,
Thermotoga, etc.

13.  pH refers to negative logarithm of hydrogen ion
concentration.
 Microbial growth is strongly affected by the pH of the
medium.
 Drastic variations in cytoplasmic pH disrupt the
plasma membrane or inhibit the activity of enzymes
and membrane transport proteins.
pH

14. Classification of bacteria according to pH

15.  Acidophiles- Grow between pH 0 and 5.5.
Examples: Ferroplasma, Thiobacillus thioxidans, Sulfolobus
acidocaldarius, etc.
 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.

16. Osmoticpressure(solutesandwateractivity)
 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.
Water activity=
Vapour pressure of solution
Vapour pressure of pure water

17. 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

18. HydrostaticPressure
 Force acting per unit area.
Classification of bacteria on the basis
of hydrostatic pressure
 Barotolerant – Does not get affected by
increased pressure.
 Barophiles/ Piezophiles- Bacteria which grow
at moderately high hydrostatic pressures.
Examples: Halomonas
salaria, xenophyophores, etc.

19. Radiation
 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.

20. References
 Microbiology, P.D. Sharma
 www.slideshare.net
 General Microbiology, C.P Powar