PHYSICAL PARAMETERS FOR GROWTH OF MICRO-ORGANISMS (BACTERIA)

 PHYSICAL PARAMETERS FOR GROWTH OF BACTERIA

Factors affecting the growth of microbes

As we know that the culture media is the nutritional substance which is necessary for growth of microorganisms. A part from the type of culture media many physical and chemical factor of the environment are also very much essential for optimum growth of micro-organisms.

PHYSICAL FACTOR FOR GROWTH OF MICRO-ORGANISM: -Following are some important Physical factors influencing the growth of microorganisms

1.     TEMPERATURE

2.     PH

3.     OSMOTIC PRESSURE

4.     HYDROSTATIC PRESSURE

5.     LIGHT AND RADIATION

6.     GASEOUS REQUIREMENTS

TEMPERATURE: - Temperature is one of the most important factors that has a great influence on the growth of micro-organism and also determines the rate of growth, multiplication, survival, and death of all living organisms. Generally high temperatures damage micro-organisms by denaturing enzymes, proteins and disrupt microbial membrane.  At very low temperatures microbial membranes solidify and enzymes also do not function properly.

TYPES OF TEMPERATURE:-

Minimum growth temperature: - The lowest temperature at which micro-organisms shows growth is the minimum growth temperature.

Optimum growth temperature;- The temperature at which the most rapid rate of growth & multiplication occurs at short period of time is optimum growth temperature.

Maximum growth temperature: - The highest temperature at which micro-organisms shows growth is maximum growth temperature.

Classification of bacteria based on temperature tolerance & its influence on growth:-

Psychrophiles/cryophiles: -

Obligate psychrophiles:- They are able to grow at 0^oc but have a optimum temperature of 15^oc or lower.

Group	Minimum Temp	Optimum Temp	Maximum Temp	Examples
Obligate psychrophiles	0 to 5	10 to 15	20	Vibrio psychroerytrus

Facultative psychrophiles: - They also able to grow at 0^oc but grow best at 20^oc to 40^oc.

Group	Minimum Temp	Optimum Temp	Maximum Temp	Examples
Facultative psychrophiles	0 to 5	25 to 30	35	Pseudomonas fluorescenes

Mesophiles: - Mesophiles are Grows best in moderate temperature & the temp range is 20^oc to 45^oc. All bacteria that are pathogenic for humans and warm blooded animals are mesophiles.

Group	Minimum Temp	Optimum Temp	Maximum Temp	Examples
Mesophiles	15 to 20	35 to 40	45	Corynebacterium Diptheriea

Thermophiles: - Heat-loving microorganisms. They prefer high temperature & the range is 45 ^oc to 80 ^oc for growth.

Facultative thermophiles: - The growth range of many thermophiles extends in to the mesophilic region (37^oc to 5^oc) are called as facultative thermophiles.

Obligate thermophiles: - They are grow at above 60^oc.

Group	Minimum Temp	Optimum Temp	Maximum Temp	Examples
Facultative thermophiles	35 to 40	50 to 55	65	Streptococcus thermophilus
Obligate thermophiles	50 to 55	65 to 70	80	Thermus Aquaticus

PH: - pH refers to negative logarithm of hydrogen ion concentration. The pH of the growth medium has a profound effect upon the growth & multiplication of micro-organisms. Drastic variations in cytoplasmic pH disrupt the plasma membrane or inhibit the activity of enzymes and membrane transport proteins.

Each microbial species has definite pH range for growth and multiplication. 

Classification of  micr-organism according to pH value:- Depending on pH value of micro-organisms they can be classified as follows.

Acidophiles: -These micro-organisms grow between pH 0 to 6.5.

E.g. Thiobacillus thiooxidans (Optimum pH 2 to 3.5), Ferroplasma, Lactobacillus acidophilus (Optimum pH 5.8 to 6.6)

Neutrophiles: - These micro-organisms grow between pH 6.5 to 7.5.  Bacteria prefer media of pH near neutrality, and usually cannot tolerate pH values much below 4-5.

E.g.  E. coli, Pseudomonas aerunginosa, Salmonella typhi & all pathogenic bacteria.

Alkalophiles: - These micro-organisms Grow between pH range of 7.5 to 14.

E.g. Thermococcus alcaliphilus, Vibrio cholera (Optimum pH 9.0), Agrobcaterium species (Optimum pH 12.0).

OSMOTIC PRESSURE: - Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of water across a SPM. Bacteria are more tolerant to osmotic variations, sudden exposure of bacteria to solutions of high salt concentration may cause plasmolysis. Hence 0.5% NaCl is added to almost all culture media to make the environment isotonic.

Types of solution:

1. Hypotonic

 2. Isotonic

3. Hypertonic

Classification of bacteria according to osmotic pressure: -

Osmotolerant: - These microorganisms are grown at relatively high salt concentration.

E.g. : Aeromonas spp, Staphylococcus spp, etc.

Halophiles: - These microorganisms are grown in the presence of salt at concentration above 0.2 to 0.6.  E.g.  Halobacterium halobium.

HYDROSTATICPRESSURE: - The pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity. (Force acting per unit area).

Classification of bacteria on the basis of hydrostatic pressure: -

Barotolerant: -These types of bacteria does not get affected by increased pressure.

Barophiles/ Piezophiles; -  Bacteria which grow at moderately high hydrostatic pressures.

E.g.  Halomonas salaria, xenophyophores, etc

LIGHT AND RADIATION: - Darkness is usually favorable for the growth and viability of micro-organisms. They are sensitive to ultraviolet radiation, direct light and other radiation.

Sunlight or visible light is beneficial because it is the source of energy for photosynthesis.

Infrared is the major source of Earth’s heat. Ionising rays can produce mutations which may result in death.

GASEOUS REQUIREMENTS: - The principle gases that affect the bacterial growth are oxygen and carbon dioxide. 

Depending on oxygen requirements bacteria can be classified as follows..

Aerobic bacteria: -These types of bacteria require oxygen for growth.

E.g.  E.coli, Staphylococcus aureus.

Anaerobic bacteria: - These types of bacteria do not  require oxygen for growth. Oxygen is toxic to such bacteria they cannot grow when incubated in an air atmosphere.

Non stringent anaerobes: - Some bacteria can tolerate low levels of oxygen and are called non stringent anaerobes.

Stringent anaerobes: - Some other bacteria who can not tolerate even low levels of oxygen and may die after brief exposure to air are called strict or stringent anaerobes.

E.g. Clostridium species.

Facultative anaerobic bacteria: - These types of bacteria do not require oxygen for growth but if oxygen is available is used for energy production. These bacteria grow in both aerobic and anaerobic conditions.

E.g. Pseudomonas species.

Microaerophilic bacteria: - These bacteria require low levels of oxygen for growth but cannot tolerate the levels of oxygen present in an air atmosphere.

E.g. Lactobacillus plantarum.

CLICK BELOW TOPIC TO READ                                                                                                         

1.      INTRODUCTION OF MICROBIOLOGY

2.      BRANCHES OF MICROBIOLOGY

3.      SCOPE OF MICROBIOLOGY

4.      HISTORY OF MICROBIOLOGY {PART 1}

5.       HISTORY OF MICROBIOLOGY {PART 2}

6.      HISTORY OF MICROBIOLOGY {PART 3}

7.        PROKARYOTES VS EUKARYOTES DIFFERENCES

8.      MORPHOLOGY OF BACTERIA

9.      ULTRASTRUCTURE OF BACTERIA

1.   NUTRITIONAL REQUIREMENTS OF BACTERIA

1.   RAW MATERIAL USED FOR CULTURE MEDIA

1.   TYPES OF CULTURE MEDIA IN MICROBIOLOGY

1.   PHYSICAL PARAMETERS FOR GROWTH

1.   GROWTH CURVE OF BACTERIA

1.   MEASUREMENT OF BACTERIAL GROWTH.

1.    ISOLATION OF PURE CULTURE