Survival versus maintenance of genetic stability: a conflict of priorities during stress.

Bacteria are constantly facing many different environmental assaults, which may be of such severity that numerous survivors have important alterations in their genetic material. Some genetic systems induced in response to such stresses, for example the SOS system and the sigmaS regulon, actively participate in the generation of genetic alterations. The key priority of those genetic systems during stress is to ensure survival. Therefore, the repair of lethal DNA lesions is an absolute necessity, while perfect restoration of original genetic information is not. Furthermore, the nature of DNA lesions might render error-free repair too costly, or even impossible for stressed bacterial cells. Although the majority of these genetic alterations are deleterious, the rare advantageous alterations may have long-term evolutionary consequences independently of whether the selection of molecular mechanisms involved in their generation is linked to survival strategies or not.