PHYSICAL FACTORS INFLUENCING THE GROWTH

OF MICROORGANISMS

Guided by:Dr. Ruchi Seth Assistant Professor - IDepartment of Biotechnology

Presented By :Prachi GuptaB.Sc. BiotechnologyI-Semester

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.

Physical factors influencing the growth of microorganisms

Temperature pH Osmotic

Pressure

Hydrostatic Pressure Radiation

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.

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 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.

Classification of bacteria according to growth temperature

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.

Mesophiles-1. Grows best in

moderate temperature.2. Temperature range: 20°C to 45°C.3. Examples: Escherichia coli,

Streptococcus pneumoniae, etc.

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.

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.

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 in Yellowstone 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.

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

Classification of bacteria according to pH

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.

Osmotic pressure (solutes and water activity)

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

Classification of bacteria according to osmotic pressure1. 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

Hydrostatic Pressure Force acting per unit area.Classification of bacteria on the

basis of hydrostatic pressureBarotolerant – Does not get affected

by increased pressure.Barophiles/ Piezophiles- Bacteria

which grow at moderately high hydrostatic pressures.

Examples: Halomonas salaria,  xenophyophores, etc.

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.

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

Thank you!