The Role of Repeat Sequences in Bacterial Genetic Adaptation to Stress

Abstract Because stress is a major component of the life history of living species, many mechanisms have been created to deal with it. Even though stress is often unpredictable, it may be overcome by mechanisms allowing the generation of genetic variability upon which natural selection can act. As a result, recent work has been aimed at identifying the elements and the mechanisms allowing the generation of such genetic variability. Among these, repeated sequences have a prominent role. Bacteria can evolve very quickly through intrachromosomal recombination between repeats, which increases significantly in times of stress. In this chapter, the instabilities produced by repeats in genes of stress response and what results from it are described. While some of these instabilities lead to deletion of genetic material, the loss of this information is not irreversible as mechanisms have evolved that facilitate its recovery. The resulting genetic variability allows the fast adaptation of bacterial populations to stresses, such as host defenses, or to toxic agents, such as antibiotics.