ADAPTIVE MUTAGENESIS - A PROCESS THAT GENERATES ALMOST EXCLUSIVELY BENEFICIAL MUTATIONS

Adaptive mutations are spontaneous mutations that occur in microorgani sms during periods of prolonged stress in non-dividing or very slowly dividing populations and that are specific to the environmental challe nge that causes that stress. This article reviews the literature on ad aptive mutagenesis since 1993. The evidence that adaptive mutagenesis is both real and generalis considered. The most widely used system for studying adaptive mutagenesis, reversion of an F'-borne lacI33 allele , is shown to be a special case that reflects more about F-plasmid bio logy than about adaptive mutagenesis in general. New evidence demonstr ating that adaptive mutagenesis is, indeed, specific is discussed. A v ariety of genes whose products affect adaptive mutagenesis are discuss ed. A model to explain that specificity and new evidence in support of that model are considered, as are potential roles of adaptive mutagen esis in evolution and practical aspects of adaptive mutagenesis.