In addition, overexpression of glycerol-3-phosphate dehydrogenase (glpD) and glycerol-3-phosphate acyltransferase (plsB) involved in energy metabolism (Spoering et al., 2006) and overexpression of relA involved in ppGpp synthesis (Korch et al., 2003) also caused increased persister see more formation. We have recently identified a new persister gene phoU, previously identified as a repressor of phosphate uptake system pstSCAB, in E. coli using a transposon mutagenesis approach (Li & Zhang, 2007). Mutation in PhoU leads to a generalized higher susceptibility than the parent strain to a diverse range of antibiotics and stresses and a defect in persister formation.

Microarray studies indicated that PhoU mutant surprizingly expressed high levels of energy metabolism genes, transporter genes and flagella and chemotaxis genes, which suggests that PhoU is a global repressor for cellular metabolism and its inactivation leads to a hyperactive metabolic state

(Li & Zhang, 2007). We thus proposed a new model of persister formation based on PhoU as a global negative regulator, which suppresses the cellular metabolism of the bacteria by downregulating or shutting down the genes or proteins involved in energy production, membrane transport, click here etc., to facilitate persister formation (Li & Zhang, 2007). However, persisters are not homogeneous (Zhang, 2004) and are most likely mediated by multiple mechanisms. To shed further light on possible new persister mechanisms, in this study, taking advantage of our successful experience of screening a transposon mutant library (Li & Zhang, 2007), we screened the E. coli Keio deletion mutant library and identified two new persister genes sucB and ubiF involved in energy metabolism, whose inactivation caused a defect in persister survival as demonstrated by higher susceptibility to different antibiotics and stresses than the parent strain. Ampicillin, norfloxacin, gentamicin, trimethoprim, tetracycline,

kanamycin and chloramphenicol were obtained from Sigma-Aldrich Chemical Co., and their stock solutions were freshly prepared, filter-sterilized and used at appropriate concentrations Exoribonuclease as indicated. Escherichia coli K-12 parent strain BW25113 and its isogenic deletion mutant library of the Keio collection (Baba et al., 2006) were used for the genetic screens to identify mutants with a defect in persister survival after antibiotic exposure. Escherichia coli cells were routinely grown in Luria–Bertani (LB) medium. For sucB and ubiF mutants, 30 μg mL−1 kanamycin was used, and for complementation of sucB and ubiF mutants, 30 μg mL−1 kanamycin and 30 μg mL−1 chloramphenicol were added. M9 minimal medium with a final concentration of 0.4% glucose and 0.05% magnesium sulfate was used as a nutrient-limiting medium. Saline (0.9% sodium chloride) was used as a condition for the starvation experiment. M9 minimal medium at pH 3.0 and 5.