PhoU Is a Persistence Switch Involved in Persister Formation and Tolerance to Multiple Antibiotics and Stresses in Escherichia coli

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Abstract
When a bactericidal antibiotic is added to a growing bacterial culture, the great majority of the bacterial population is killed but a small number of metabolically quiescent bacteria called persisters survive antibiotic treatment. The mechanism of this bacterial persistence is poorly understood. In Escherichia coli, we identified a new persistence gene, phoU, whose inactivation leads to a generalized higher susceptibility than that of the parent strain to a diverse range of antibiotics, including ampicillin, norfloxacin, and gentamicin, and stresses, such as starvation, acid pH, heat, peroxide, weak acids, and energy inhibitors, especially in stationary phase. The PhoU mutant phenotype could be complemented by a functional phoU gene. Mutation in PhoU leads to a metabolically hyperactive status of the cell, as shown by an increased expression of energy production genes, flagella, and chemotaxis genes and a defect in persister formation. PhoU, whose expression is regulated by environmental changes like nutrient availability and age of culture, is a global negative regulator beyond its role in phosphate metabolism and facilitates persister formation by the suppression of many important cellular metabolic processes. A new model of persister formation based on PhoU as a persister switch is proposed. PhoU may be an ideal drug target for designing new drugs that kill persister bacteria for more effective control of bacterial infections.