Genetic response of microbes to extreme challenges.

Bacteria are capable of surviving in a wide range of seemingly impossible situations. In the main part this is because very large numbers of individual cells are involved, so that even very rare mutations will occur often enough to solve most acute problems and permit growth. But in addition, bacteria have evolved in an environment that has fluctuated so often in the past that they may have evolved a group of "last ditch" mechanisms to meet these challenges. These include developing a metabolically inactive state; activating previously evolved, but silent genes; increasing rates of mutation under dire condition; and favoring movement of exogenous and endogenous genetic elements. Some of these processes can function to make it appear that directed "Lamarckian" mutations have occurred. Together these survival mechanisms constitute the "catastrophe insurance" of the cells.