Classification Of Microorganism On The Basis Of Growth Temperature

On the basis of temperature range required for the growth of microorganism, they are divided into five classes. This are mentioned below:

Psychrophiles

Psychrophiles or Cryophiles are capable of growing and reproducing at a temperature of 0°C i.e. they are extremophilic organism. They have an optimum growth temperature of 15°C or less. Most of the psychrophilic organisms are bacteria, like genera Bacillus, Pseudomonas, Alcaligenes, Vibrio, Arthrobacter, Moritella, Photobacterium etc. They are very well adapted to low temperature and most of them cannot survive at a temperature higher than 20°C. Their enzymes, protein synthetic machinery and transport system are well adapted to low temperature. Their cell membrane contains high level of unsaturated fatty acid to keep it in semifluid form.

Psychrotrophs

Psychrotrophic bacteria, also known as facultative psychrophiles, are capable of surviving in cold environment; they can grow at a temperature range of 0 to 7°C. They have an optimum growth temperature of 20 to 30°C, with a maximum of 35°C. They are generally found in soils, in surface and deep sea waters. They are responsible for the spoiling of refrigerated foods.

Mesophiles

Mesophiles grows at moderate temperature, with optimum growth temperature of around 20 to 45°C. Majority of the microorganisms are mesophiles, including all the human pathogens. For instance: Staphylococcus aureus, Thiobacillus novellus, Streptococcus pyogenes, Listeria monocytogenes, Escherichia coli etc. They are involved in wine and beer making, and they are also found in cheese and yogurt.

Thermophiles

Thermophiles are extremophilic organism that grow at a temperature of 55°C or higher. The minimum temperature required for their growth is 45°C. Majority of thermophiles are archaea, however it includes bacteria, fungi and algae also. They are generally found in various geothermally heated regions of the Earth, such as hot water lines, hot springs and also in decaying plant matter like compost. They are able to survive such a high temperature because they have heat stable enzymes like heat stable DNA polymerase and protein synthesis system that works well at high temperature. Their cell membrane contains high level of saturated fatty acid, therefore having higher melting point and thereby membranes remains unharmed at such temperature. Example of thermophiles include Campylobacter jejuni.

Hyperthermophiles

Hyperthermophiles can grow at 90°C or above i.e. in extremely hot environments. They can tolerate temeparature of around 100 °C. Examples of hyperthermophiles include Pyrococcus abyssi, Aquifex aeolicus, Pyrodictium occultum etc. Their cell membrane contains high level of saturated fatty acid, which helps in maintaining shape at such a high temperature.