Types of Micro-organisms on the basis of Temperature

Effect of Environment on the growth of Micro-organism

  • The chemical and physical conditions of the environment have a great effect on the growth and activities of micro-organisms.
  • Environmental conditions such as temperature, ph, hydrogen ion concentration, osmotic pressure, heavy metals and ultraviolet ray have a great influence on the growth of micro-organism.
  • In this article, we are going to see the effect of temperature on the growth of micro-organism and types of micro-organism on basis of temperature.
  • Change in temperature effects micro-organisms in two ways

1.As the temperature increases the rate of biochemical reaction increases until enzyme activity is stable. But at a certain point, the change in temperature may cease growth of the organism and result in the lethal condition.

2.High-temperature damage micro-organism by denaturing enzymes, proteins, cell membranes etc.

Important Terms

  • Thermal death point – it is the lowest temperature that is required to kill the standard suspension of micro-organism within 10 minutes.
  • Thermal death time – it is the shortest time that is required for killing the standard suspension of micro-organism at a definite temperature.
  • Decimal reduction time – it is a time that is required to kill the population of micro-organisms by 90% at a specific temperature.
  • Each and every micro-organism has a cardinal range of temperatures for its growth and they are minimum temperature, optimum temperature and maximum temperature.
  1. Minimum temperature – the temperature below which growth of microbes does not take place is called minimum growth temperature.

  2. Optimum temperature – the temperature at which there is a maximum growth of microbes is called an optimum growth temperature.

3. Maximum temperature – the temperature above which the growth of microbes doesn’t take place is called as maximum growth temperature.

On the basis of the Temperature range, the micro-organisms are divided into three groups and they are

 1. Psychrophiles

  • Psychrophiles are the organisms that grow at low temperature. ‘Psychros’ means cold and ‘philic’ means loving or prefer to.
  • These psychrophiles grow well at low temperature because the metabolic activates such as protein synthesis, enzyme functioning, transport system work efficiently at low temperature. Whereas psychrophilic microbes have high levels of unsaturated fatty acids in the cell membrane and this fatty acid remain semifluid conditions during cold temperature.

1. The minimum temperature for growth is 0 degree Celsius.

2. The optimum temperature for growth is 15 degree Celsius or it may be lower than that.

3. The maximum temperature for growth is 20 degree Celsius.

  • The organism that grows at 0 degree Celsius and the optimum temperature is 20 to 30 degree Celsius and the maximum temperature is 35 degree Celsius are called as Psychrotrophs. These psychotropic bacteria are responsible for spoilage of refrigerated food.
  • The common habitat of psychrophiles is cold regions like arctic and Antarctic region.
  • Psychrophiles are unable to grow above 20 degree Celsius because due to increase in heat the ribosome and other enzymes becomes unstable and which increases membrane disruption resulting in leakage of cell constituents and finally result in lysis of the cell.
  • Examples of psychrophiles are Chlamydomonas nivalis, Achromobacter, Pseudomonas, Serratia, Candida and Alcaligenes.

2. Mesophiles

  • Mesophilic bacteria are the bacteria that grow in the middle or we can say the normal temperature range. ’ Meso’ means middle or medium and ‘philic’ means loving or prefer to. Most of the bacteria fall in mesophilic bacteria group.
  1. The minimum growth temperature of mesophilic bacteria is 15 to 20 degree Celsius.

2. The Optimum growth temperature range of mesophilic bacteria is 20 to 45 degree Celsius.

3. The maximum growth temperature of mesophilic bacteria is less than 45 degree Celsius.

  • The pathogenic micro-organism is mesophilic in nature as well as the microflora that is present in soil and water also fall in the mesophilic group.
  • Examples are Escherichia coli, Staphylococcus aureus, Corynebacterial diphtheria, Streptococcus aureus, etc

3. Thermophiles

  • Thermophiles are the micro-organism that grows at high temperature that is above 40 to 50 degree Celsius.
  • ‘ Thermo’ means heat and ‘philic’ means prefer to that means high temperature loving microbes.

1. The minimum growth temperature of thermophilic bacteria is 40 to 42 degree Celsius.

2. The optimum growth temperature of thermophilic bacteria is 65 to 70 degree Celsius.

3. The maximum growth temperature of thermophilic bacteria is 70 degree Celsius.

4. The thermophilic bacteria having optimum growth temperature of 50 to 60 degree Celsius but can also grow at room temperature is called as facultative thermophilic bacteria.

  • Thermophilic bacteria are commonly found in hot temperature habitats like hot springs, compost piles and volcanic areas.
  • There are few algae, fungi and bacteria that are thermophilic in nature.
  • Some thermophilic bacteria can also be isolated from milk and soil samples.
  • The thermophilic bacteria are able to survive at high temperature because their metabolic activity works well at high temperature as well as the enzymes, protein and cellular components are much resistant at high temperature. The saturated fatty acids present in the cell membrane have the high melting point so remain unaffected or stable at high temperature.
  • Examples of thermophilic micro-organism – Bacillus, Clostridium, Sulphurous and Thermococcus.

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