title: Copper tolerance mediated by polyphosphate degradation and low-affinity inorganic phosphate transport system in Escherichia coli.
abstract: BACKGROUND
  Metal tolerance in bacteria has been related to polyP in a model in which heavy metals stimulate the polymer hydrolysis, forming metal-phosphate complexes that are exported. As previously described in our laboratory, Escherichia coli cells grown in media containing a phosphate concentration >37 mM maintained an unusually high polyphosphate (polyP) level in stationary phase. The aim of the present work was to evaluate the influence of polyP levels as the involvement of low-affinity inorganic phosphate transport (Pit) system in E. coli copper tolerance.
  
  
  RESULTS
  PolyP levels were modulated by the media phosphate concentration and/or using mutants in polyP metabolism. Stationary phase wild-type cells grown in high phosphate medium were significantly more tolerant to copper than those grown in sufficient phosphate medium. Copper addition to tolerant cells induced polyP degradation by PPX (an exopolyphosphatase), phosphate efflux and membrane polarization. ppk-ppx- (unable to synthesize/degrade polyP), ppx- (unable to degrade polyP) and Pit system mutants were highly sensitive to metal even in high phosphate media. In exponential phase, CopA and polyP-Pit system would act simultaneously to detoxify the metal or one could be sufficient to safeguard the absence of the other.
  
  
  CONCLUSIONS
  Our results support a mechanism for copper detoxification in exponential and stationary phases of E. coli, involving Pit system and degradation of polyP. Data reflect the importance of the environmental phosphate concentration in the regulation of the microbial physiological state.
authors.forename: Mariana
authors.initials: M
authors.lastname: Grillo-Puertas
authors.forename: Lici Ariane
authors.initials: LA
authors.lastname: Schurig-Briccio
authors.forename: Luisa
authors.initials: L
authors.lastname: Rodríguez-Montelongo
authors.forename: María Regina
authors.initials: MR
authors.lastname: Rintoul
authors.affiliation: Instituto Superior de Investigaciones Biológicas, INSIBIO (CONICET-UNT) and Instituto de Química Biológica "Dr Bernabé Bloj", Facultad de Bioquímica, Química y Farmacia (UNT), Chacabuco 461 CP T4000ILI, Tucumán, Argentina. vrapisarda@fbqf.unt.edu.ar.
authors.forename: Viviana Andrea
authors.initials: VA
authors.lastname: Rapisarda
mesh_terms: D017766:Acid Anhydride Hydrolases / Q000235:genetics; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000378:metabolism*; D003300:Copper / Q000378:metabolism* / Q000633:toxicity; D000073840:Copper-Transporting ATPases; D003470:Culture Media / Q000737:chemistry; D004361:Drug Tolerance; D004926:Escherichia coli / Q000187:drug effects* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics; D009154:Mutation; D010710:Phosphates / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics; D011122:Polyphosphates / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D027682:Cation Transport Proteins; D003470:Culture Media; D029968:Escherichia coli Proteins; D010710:Phosphates; D011122:Polyphosphates; D003300:Copper; D017853:Phosphotransferases (Alcohol Group Acceptor); C475691:polyphosphate kinase, E coli; D017766:Acid Anhydride Hydrolases; D000251:Adenosine Triphosphatases; C513394:Ppx protein, Escherichia coli; D000073840:Copper-Transporting ATPases; C000612460:copA protein, E coli