Thermophilic bacteria are extremophiles; they live in the sorts of temperatures that would toast other organisms. Strictly speaking they are not bacteria, but members of a different branch of life known as Archaea.
Thermophiles like it hot, really hot. They live and reproduce in a sizzling temperature range that could be anywhere between 45 and 80 degrees Celsius. The record breaker is an even more extreme kind of extremophile and it's called Strain 121 - so named because it flourishes in temperatures of 121 degrees Celsius. That's much hotter than the boiling point of water.
There aren't too many places on the planet that can provide such a hot home for these organisms, but they are found in hot springs such as those in Yellowstone National Park, and in deep sea hydrothermal vents. These are cracks in the Earth's surface underwater through which magma seeps and superheats the water.
The phrases thermophilic bacteria and heat-loving bacteria are still in common use, but these microorganisms are not bacteria.
They were discovered in the 1960s by Thomas Brock who found them growing in the boiling hot springs at Yellowstone. But it was in the 1970s and the work of Dr Carl Woese and colleagues at the University of Illinois that led to their classification in a new domain of life. So different is their genetic makeup from bacteria that Woese proposed a new domain - Archaebacteria. The bacteria part of the name was later dropped in recognition of the fact that they are biochemically and genetically different from bacteria. The domain is now known as Archaea.
How Comes they Like it So Hot?
So how are thermophiles able to keep their cool when all around them is bubbling away?
Their enzymes, proteins, and DNA are not only heat stable, but they work best in extreme temperatures. This is achieved by a number of neat little chemical tricks that stop them from denaturing and falling apart in the sizzling heat.
First of all there are a few small changes in the amino acids - some charged residues such as arginine and lysine form more ion pairs, and there can be more polar amino acids that form hydrogen bonds. All of which contributes to proteins folding in such a way that they are resistant to the destructive effects of heat. Protein stability is also achieved by the formation of an increasing number of bonds between different parts of a protein molecule.
The thermophiles exist in conditions that would melt the DNA of other organisms. However, the heat-loving microbes are able to keep their DNA intact through a number of different ways including: -
- Higher levels of salts such as potassium and magnesium which prevent the phosphodiester bonds from degrading
- The DNA of some thermophiles is supercoiled - the double-stranded DNA is further twisted which confers heat stability.
Limits of Life
It is generally believed that no microorganism could survive in temperatures over 150 degrees Celsius, although this has not been proven yet. No organism has been found in these temperatures, but that doesn't necessarily mean that they don't exist.