Besides the production of defensive compounds and enzymes that can be used against competitors, many microorganisms have developed a variety of protective mechanisms against the toxins from other organisms: the cell membrane, drug exporters, restriction enzymes, or rapid mutational adaptation. The cell membrane of microorganisms together with extracellular enzymes provides a first line of protection against penetrating organisms or toxins. Drug exporters pump out poisonous compounds from the cells and thus prevent toxins to exert their destructive potential. Restriction enzymes destroy foreign DNA and thus kill organisms that have entered the cells. The short generation cycle of microorganisms allows them to rapidly adapt their genome to challenges from the environment. For example, antibiotic resistance is often quickly acquired (see Evolution of Defense Strategies).
A fascinating example for a highly specialized microorganism is Deinococcus radiodurans that contains four to ten copies of its genome in a cell and in addition has a highly efficient DNA-repair system that enables it to reassemble its genome even if it was considerably destroyed. This organism is not only very stable against desiccation and UV light but also against ionizing radiation.
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