Cold
Welcome Cold
Welcome Now we have seen how bacteria adapt to extreme heat, it’s time to examine their reactions to the opposite extreme. Temperatures on earth do not fall as far as many think – the sea never falls much below 2°C but in some lakes or sea beds with an exceptionally high salt concentration, this may fall to –5°C or in extreme cases, -12°C.
The bacteria that live in these conditions are called psychrophiles (cold lovers – they die much above 20°C) and psychrotrophs, which can live at low temperatures but prefer more normal ones.
Psychrophiles is pronounced as sigh-crow-file
Psychrotroph is pronounced as sigh-crow-trowf
Why is it so hard to live in temperatures just a bit less than the 20°C that is so comfortable for us?
There are three main problems
· Our cells carry out thousands of chemical reactions vital to life – at lower temperatures these reactions slow disproportionately may have almost stopped when 10°C is reached.
· All cells have a thin, fatty acid membrane (mentioned in previous section). This is made of fats and can harden at low temperatures, preventing vital materials entering and leaving the cell.
· Cells contain a lot of water – when this freezes, ice can form and this can cause the cells to rupture.
Psychrophiles and psychrotrophs have solved the first problem in different ways.
· Psychrophiles have evolved new enzymes that allow their vital reactions to occur at nearly normal speeds under very low temperatures – the down side of this is that these enzymes do not works at higher temperatures (possibly the reason that they die above 20°C).
· Psychrotrophs, by contrast, are happiest at temperatures above 20°C. They can tolerate low temperatures as they have methods for adapting to the cold and allowing their chemical reactions to proceed – this is not as effective a solution as the psychrophiles however – they grow at temperatures below 6°C, but only very slowly.
The fatty acid membrane of psychrophiles is made of special fats that do not turn hard at low temperatures – unfortunately, this means that they melt more easily at higher temperatures.
Many bacterial cells actually contain a substance similar to anti-freeze. This prevents theme rupturing as temperatures descend past the freezing point of water.
Importance to us: As with thermophiles, some of the enzymes of psychrophiles are proving useful in industry – allowing low temperature reactions that would otherwise be difficult to achieve such as the sweetening of milk or the production of medically useful substances – these can be done at higher temperatures but much less efficiently. In the wild, psychrophiles are mainly to be found on the seabed – they feed upon the detritus of the world above and return useful elements to the environment. Without these organisms, much of the world’s resources would end up locked away at the bottom of the deep cold sea.