Study of persister cells (reversible drug-tolerant phenotypes) that are observed in both bacterial and cancer cell populations. These phenotypes generally exist in a transient, growth-inhibited state. They can be formed stochastically or induced by environmental factors. The cells are thought to underlie the propensity of recurrent diseases to relapse, and little is known about the physiology of these rare sub-populations. Deeper understanding of the molecular make-up of these phenotypic variants will facilitate the development of therapeutics. Therefore, a major goal of the research is to study their physiology: the metabolite, RNA, protein, and regulatory content that allow them to tolerate extraordinary concentrations of drugs.