How resilient is life?

Life Underwater



It is commonly thought that life on Earth evolved because the Earth is in the Goldilocks Zone of the Sun and thereby created moderate and nurturing conditions for life to evolve. This thought may be true for regular organisms like mammals and plants, but there are some life forms that can survive or even thrive in extreme conditions. These organisms are known as Extremophiles. The word Extremophiles is a combination of two words. They are Extreme and Philus which means lover in Greek. Extremophiles can survive in almost all harsh conditions imaginable. Extremophiles can be classified into three broad kingdoms. They are as shown:

1. Thermophiles: These bacteria contain special enzymes that contain disulphide bonds. The enzymes enable the bacteria to thrive in high temperatures. These bacteria can thrive in temperatures from 45 to 80 degree Celsius. Some organisms like the tube worms found in the abyssal zone of the Atlantic Ocean, harbor Thermophiles to survive the hot springs or thermal vents and to extract nutrients from the vents. There is another class of thermophiles that can thrive in temperatures from 80 degrees Celsius to 120 degrees Celsius. That class of Thermophiles is called Hyper Thermophiles. Thermophiles are used in Molecular Genetics, Medical Diagnostics, Dairy Production, and Methane or Natural Gas production. An example of a Thermophile would be Alicyclobacillus.

Photo of Alicyclobacillus. Source: HRS Heat Exchangers


2.  Psychrophiles: These bacteria contain an anti-freeze protein that enables them to thrive in cold conditions without freezing. They can withstand temperatures from zero to minus fifteen degrees Celsius. They have been found buried in ice up to two meters deep. Psychrophiles are used in freezing applications, bio remedy and in biosensors. An example of psychrophilic bacteria is Psychrobacter.

Photo of Psychrobacter. Source: MiDAS field guide.


3.  Halophiles: These bacteria thrive in extreme levels of salt in their environment. They absorb the nutrients from the salt and make extra copies of their DNA. They then use the replicated DNA to survive when nutrients (salt) is no longer available. These bacteria have been found in the Dead Sea and The Great Salt Lake. They are used in oil drilling, waste treatment,  and dietary supplementation. They are also hosted by Tube Worms in the abyss to absorb nutrients from the poisonous sulphides that pour out from the underwater thermal vents. An example of Halophiles is Halobacterium.

Photo of Halobacterium. Source:


4. Acidophiles:  These bacteria can survive in highly acidic conditions i.e., in a pH as low as 1. Their insides have a pH close to neutral (7) and they derive nutrients from acidic gases like CO2 and H2S. They maintain a Proton Gradient over their Cytoplasmic Membranes of up to five orders of magnitude. That’s how they survive highly acidic conditions. They are used in recovering metals from their ores and desulphurisation of coal. An example of Acidophiles is Thiobacillus

Picture of Thiobacillus. Source: Blog Coral Wonders


5. Alkaliphiles: These bacteria can survive in highly alkaline conditions i.e., in a pH as high as 10. Their cell walls contain acidic polymers that prevent Hydroxide ions from entering into the cell. They are able to absorb Sodium and Hydrogen ions from the alkalis for their nutrition. They are found in the sulphurous hot springs of Yellowstone National Park. Flamingos (both greater and lesser flamingos) host these bacteria to help them survive in the alkaline lakes in the mountain tops. Those lakes contain a type of shrimp that the flamingos feed on and are also rich in dissolved Sodium Carbonate, which is alkaline. The Flamingos get their pink colour due to these bacteria that they host. Alkaliphiles are sometimes used in acidity tonics and tablets and to treat industrial waste. An example of Alkaliphiles is Bacillus Pseudofirmus.

Photo of Bacillus Pseudofirmus. Source: Geotesc


Some extremophiles are Polyextremophiles. These types of organisms possess all the characteristics of all the types of extremophiles discussed above. They can are able to survive in any condition be it hot or cold or high pressure or low pressure or high salinity or highly acidic or highly alkaline conditions. They can even survive in the cold vacuum of space for 120 days. One such Polyextremophile is the Tardigrades, more commonly known as the Water Bear. It can go for decades without food or water! When conditions are very harsh, it curls its body up and lowers its metabolism rate by 90%. This state is called as suspended animation.

When conditions are right again, its body kicks back to life and its metabolism rate returns to normal. We should be thankful that this creature is microscopic. Had it been any larger, it would have taken over the Earth, perhaps even all the planets in the solar system. Water Bears are able to extract nutrients from any mineral including poisonous sulphides and phosphates. They are ‘The Survivors’ of the universe. There is no organism known to mankind that can survive better in extreme conditions than Tardigrades. It just goes to show that size does not always count in survival.

Photo of Tardigrades. Source: Science News

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