Topoisomerase function during bacterial responses to environmental challenge.

Every living organism needs to have multiple defense mechanisms against environmental challenge for survival during evolution. Rapid changes in gene expression have been demonstrated during bacterial adaptation to environmental stress. Since DNA supercoiling varies in response to environment, and since supercoiling is known to influence strand separation in DNA, and therefore many vital cellular processes, including transcription, supercoiling could potentially serve as a molecular mechanism through which expression of many genes could be influenced by the environment. The relationship between changes in DNA topology and a number of environmental stress conditions including high temperature, oxidative stress and extreme pH, is reviewed here. The activities of DNA gyrase and topoisomerase I are key components in determining the degree of bacterial DNA supercoiling. The specific involvement of topoisomerase function in bacterial adaptation to these environmental stress conditions, as demonstrated by the effect of mutations or inhibitors on adaptation and survival for these potentially lethal conditions, is also reviewed.