Microorganisms which live in extremely hostile environments are called extremophiles. These organisms can survive extreme temperatures, high salinity environments, very acidic or alkaline environments and even intense radiation. Most of these organisms use anaerobic respiration to derive energy, though aerobic respiration is observed in a few species.

Types of Extremophiles

• Organisms that are able to achieve optimal growth at temperatures above 45 °C are called These organisms are usually found in environments such as hot springs and natural geysers.

• On the other end of the spectrum are the Cryophiles, which reach optimal growth temperatures below 15 °C. These are found in polar regions as well as at the deep end of oceans.

• Organisms that are able to survive radiation, especially the high energy ionizing radiation, are called These organisms can survive doses of radiation that can easily kill an adult human.

• If an organism thrives in an environment with a very high concentration of dissolved salts, it is known as a The name itself means “salt-loving”, which is derived from Greek.

• Anaerobe is another type of extremophile which grows best in the absence of oxygen. There are two subtypes under anaerobes – obligate and facultative. An obligate anaerobe dies in the presence of oxygen while a facultative anaerobe can tolerate oxygen.

• Organisms that grow best in very acidic environments are called acidophile. The optimum pH level for such organisms are 3.0 or lower.

• Alkaliphiles are organisms that require a pH level of 9.0 or above. Some of these organisms can be found in alkaline lakes with high salinity levels.

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