Roles of CRISPR in regulation of physiological processes

It is now well established, following numerous independent studies, that the CRISPR-Cas system is an adaptive immune system widespread in bacteria and archaea. The primary role of CRISPR-Cas in protection against foreign DNA is nowadays undisputed. However, there is also strong evidence suggesting that, at least in some organisms, CRISPR-Cas systems have adapted to take nonimmune-related regulatory roles that are hardwired into the core regulatory programs of bacterial physiology. In at least two cases, CRISPR was shown to regulate bacterial social behavior; in other cases, CRISPRs were suggested to directly regulate endogenous gene expression. Curious cases of CRISPR-derived autoimmunity were also described. This chapter discusses major examples of such nonimmune roles of CRISPR-Cas that were described to date, their putative mechanisms of action, and their functional and evolutionary implications.