1 physical factors

factors affecting growth of microorganism

1. Physical factors influencing the growth of microrganism Guided by: Presented by: Dr.Monika sogani Raj & Sakshi sharma Associate professor Bsc biotecnology Manipal university jaipur iv 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 factor of their environment. Physical factor- temperature,pH ,osmotic pressure, hydrostatic pressure, and radiation Chemical factors- oxyegen , carbon,nitrogen,phosphorus,sulfur,etc .

3. Physical factors influencing the growth of microorganism

4. Temperature Temperature is the most important factor that determines the rate of growth, multiplication, survival, and death of all living organisms. High temperatures damages microbes by denaturing enzymes,transport carriers and other proteins. Microbial membranes are disrupted by temperatures extremes. At very low temperature membranes also solidify and enzymes also do not fuction properly

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

6. Minimum growth temperature The lowest at which organism grow is the minimum growth temperature. Optimum growth temperature The temp at which the most rapid rate of multiplication growth. Maximum growth temperature The highest at which growth occurs. A temperature o nly slightly above this point frequently kills the microorganisms by inactivating critical enzyme s

7. Growth rate v/s temperature

8. Classification of bacteria according to growth temperature

9. Cryophiles - The term cryophiles was first used by S.Schmidth -Nelson. Extremeophilic organism that are capable of growth and reproduction in cold temperatures. Temperature range:-20 ̊C TO +10 ̊C. Examples: Oscillatoria , chlamydomnas nivalis,methanogenium , etc.

10. mesophiles Grows best in moderate temperature. 2. Temperature range: 20 ̊C to 45 ̊C. 3. Example: Escherichia coli , strptococcus phneumonia , etc

11. psychrotrophs Have optimal and maximal growth temperatures above 15 and 20 ̊C respectively. Pyschrotrophic bacteria and funji are the principal cause of spoilage of refrigerated food. Example: pseudomonas , Aeromonas , Bacillus, Clostridium etc. Cold tolerant bacteria.

12. T hermophiles Derived from greek word thermotita meaning heat and philia meaning love. Heat loving ,microorganism. Grow at 50 ̊C or higher. Their growth minimum is usually around 45 ̊C amd often optima between 50 to 80 ̊C. Examples: Thermus aquaticus,Geogemma barassil,etc .

13. H yperthermophiles Thrives in extremely hot environments. Temperature range: 80 C to 113 C. First discovered by T homas d.Brock in 1965, in hot springs in yellowstone national park. The cell membranes contain high levels of saturated fatty acids to retain its shape at high temperatures. Examples : Sulfolobus , Methanococcus jannaschii , thrmotogo , etc

14. pH 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 inhinit the activity of enzymes and membranes transport proteins.

15. Classification of bacteria according to pH

16. Acidophiles Grow between pH 5.5 Example: T hiobacillus thioxidans , sulfobolous acidocaldarius etc. Alkalophiles -grows between ph range 7.5to 14. Ex- T hermococcus alcaliphilus , etc Neutrophiles - grow between ph 5.5 to 8.0. Ex- Lactobacillus acidophillus , E.coli etc. Bacteria prefer media of ph near neutrally and usually cannot tolerate pH value much below 4-5

17. What about microbes that live at pH extremes ? Drastic variations in cytoplasmic pH can harm microorganisms by disrupting the plasma membrane or inhibiting the activity of enzymes and membrane transport proteins. Most microbes die if the internal pH drops much below 5.0 to 5.5. Changes in the external pH also can alter the ionization of nutrient molecules and thus reduce their availability to the organism. Extreme alkaliphiles such as Bacillus alcalophilus maintain their internal pH dose to neutrality by exchanging internal sodium ions for external protons. Acidophiles use a variety of measures to maintain a neutral internal pH. These include the transport of cations (e.g., potassium ions) into the cell, thus decreasing the movement of H+ into the cell; proton transporters that pump H+ out if they get in; and highly impermeable cell membranes.

18. Oxygen concentration The importance of oxygen to the growth of an organism correlates with the, processes it uses to conserve energy. Almost all energy-conserving metabolic processes involve the movement of electrons through a series of membrane-associated electron carriers called an electron transport chain (ETC). . Oxygen serves as the terminal electron acceptor for the ETC in the metabolic process called aerobic respiration. In addition, aerobic eukaryotes employ Oz in the synthesis of sterols and unsaturated fatty acids. Facultative anaerobes do not require Oz for growth but grow better in its presence. In the presence of oxygen, they use O2 as the terminal electron acceptor during aerobic respiration.

19. The different relationships with 02 are due to several factors, including the inactivation of proteins and the effect of toxic O2 derivatives . Enzymes can be inactivated when sensitive groups such as sulfhydryls are oxidized. Toxic O2 derivatives are formed when cellular proteins such as flavoproteins transfer electrons to 02• These toxic O2 derivatives are called reactive oxygen species (ROS), and they can damage proteins, lipids, and nucleic acids. ROS include the superoxide radical, hydrogen peroxide, and the most dangerous hydroxyl radical.

20. most dangerous hydroxyl radical .

21. Pressure Organisms that spend their lives on land or the surface of water are always subjected to a pressure of 1 atmosphere ( atm ; 1 atm is -0.1 megapascal , or MPa for short) and are never affected significantly by pressure. Other organisms, including many bacteria and archaea , live in the deep sea (ocean depths of 1,000 m or more), where the hydrostatic pressure can reach 600 to 1,100 atm and the temperature is about 2 to 3°C. These high hydrostatic pressures affect membrane fluidity and membrane-associated function.

22. Radiation Ultraviolet (UV) radiation can kill microorganisms due to its short wavelength (approximately from 10 to 400 nm) and high energy. The most lethal UV radiation has a wavelength of 260 nm, the wavelength most effectively absorbed by and damaging to DNA . Longer wavelengths of UV light (near-UV radiation; 325 to 400 nm) can also harm microorganisms because they induce the breakdown of the amino acid tryptophan to toxic photoproducts. These toxic photoproducts plus the near-UV radiation itself produce breaks in DNA strands . Even visible light, when present in sufficient intensity, can damage or kill microbial cells. Usually pigments called photosensitizers and 02 are involved

23. Solutes and Water Activity A selectively permeable plasma membrane separates microorganisms from their environment, they can be affected by changes in the osmotic concentration of their surroundings . If a microorganism is placed in a hypotonic solution (one with a lower osmotic concentration), water will enter the cell and cause it to burst unless something is done to prevent the influx of water or inhibit plasma membrane expansion . Conversely, if it is placed in a hypertonic solution (one with a higher osmotic concentration), water will flow out of the cell. In microbes that have cell walls, the membrane shrinks away from the cell wall-a process called plasmolysis .

24. . These osmophiles include Some microbes are adapted to extreme hypertonic environments halophiles , which require the presence of NaCl at a concentration above about 0.2 M. The first approach used by halophiles is to maintain high levels of inorganic compatible solutes such as potassium chloride ( KCl ) in the cytoplasm. The second approach is to increase the internal osmotic concentration with organic compatible solutes such as choline , betaine , and amino acids such as proline and glutamic acid

25. Reference http://www.nptel.ac.in Prescotts in microbiology

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