Perhaps the best known
bacterial adaptation to stress is the formation of endospores. Endospores are
bacterial survival structures that are highly resistant to many different types
of chemical and environmental stresses and therefore enable the survival of
bacteria in environments that would be lethal for these cells in their normal
vegetative form.
It has been proposed that endospore formation has allowed for
the survival of some bacteria for hundreds of millions of years (e.g. in salt
crystals)although these publications have been questioned. Endospore formation
is limited to several genera of gram-positive bacteria such as Bacillus and
Clostridium. It differs from reproductive spores in that only one spore is
formed per cell resulting in no net gain in cell number upon endospore
germination. The location of an endospore within a cell is species-specific and
can be used to determine the identity of a bacterium. Dipicolinic acid is a
chemical compound which composes 5% to 15% of the dry weight of bacterial
spores and is implicated in being responsible for the heat resistance of
endospores.
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