The idea of immortality has sparked human interest for thousands of years so it would be extremely ironic if tiny creatures we cannot even see unaided had achieved this goal. Many microbiologists think that they have – they believe that a bacterium will not die unless it is killed (by predation, starvation, environmental change or physical damage). Even the last three of these are not certain, as many bacteria have evolved survival mechanisms to allow them to withstand adverse environmental changes and starvation.
A good example of this is called an endospore – when certain types of bacteria become low on food they start to produce a special seed-like structure called an endospore. This structure is much smaller that the original bacterium and contains a copy of its DNA in a thick walled structure from which almost all of the water has been removed. When the spore reaches a food-rich location it can ‘hatch’ to form bacterium of the original type.
These spores (very different from the spores of fungi) are incredibly resistant to heat (up to 120°C) and radiation and can survive in an inactive form for almost unimaginable lengths of time. One researcher claims several thousands of years for bacteria that were grown from spores within an Egyptian tomb, while another claims over 40 million years for spores taken from the gut of an insect frozen in amber – these spores yielded live bacteria when they were put onto appropriate nutrient.
Endospores are not the only survival mechanism – though they are believed to be the most resistant. Even more complex is the mechanism used by a type of bacteria called Myxococcus.
When food for this organism becomes scarce, the tiny individual bacterium can migrate toward each other and group together to form a mound – this mound then becomes what is known as a fruiting body. This effectively means that single cells are coming together to make a multi-celled organism – some of the cells in this organism change into myxospores – a survival ‘life pod’ similar in function to the endospores but not as hardy.
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