RAPISARDA Viviana Andrea
congresos y reuniones científicas
Copper detoxification in Escherichia coli via polyphosphate and inorganic phosphate transport system.Best Oral Communication Prize, The American Society for Microbiology (ASM)
Congreso; IX Congreso SAMIGE 2013; 2013
E. coli is equipped with multiple enzymatic systems to safeguard the citoplasmic and periplasmic space from copper-induced toxicity. Metal tolerance was also related to inorganic polyphosphate (polyP). The main enzymes associated with polyP metabolism are polyphosphate kinases (PPK) and exopolyphosphatase (PPX), encoded by ppk and ppx genes, respectively. In arquea was proposed that intracellular cations would activate PPX, with concomitant polyP degradation. The complex Pi-cation generated would be removed from the cell through the inorganic phosphate transport (Pit) system. In our laboratory, it has been demonstrated that E. coli cells presented high viability, low oxidative damage and elevated resistance to external H2O2 stress when Pi concentration in the growth medium was above 37 mM. All those events were related to an unusual maintenance of high polyP levels in stationary phase. The aim of this work was to examine the copper tolerance mediated by polyP levels and Pit system in stationary E. coli cells grown in sufficient (MT, 2 mM Pi) and high (MT+P, 40 mM Pi) phosphate media. We found that MT wild-type (WT) cells were sensitive to 0.2 mM Cu2+, whereas MT+P WT cells showed tolerance up to 4 mM Cu2+. pitAand pitB- strains were sensitive to 0.5 mM Cu2+ in both media, being pitA- pitB- susceptible at 0.25 mM. ppkppx and ppx mutants were not able to tolerate Cu2+ concentrations higher than 0.5 mM even when they were grown in MT+P. As previously described for WT, Pit mutants maintained high polyP levels in stationary phase in MT+P, whereas in MT an abrupt decrease was observed. As expected, in ppx- polyP was maintained high in both media. A decrease in polymer level was observed in MT+P medium in a copper concentration-dependent way in WT and pitA- pitB-, however no polyP degradation was observed in ppx mutant with all tested copper concentrations. Pi efflux was observed after Cu2+ addition to stationary MT+P cells, being higher in WT than in pitA and pitB mutants. Pi release was undetectable in pitA- pitB- cells. Addition of copper ions produces high changes in cellular membrane potentials only in MT+P WT cells. In this work we demonstrated a relationship between copper concentrations and polyP levels in E. coli, supporting a model for metal tolerance mediated through Pit transporter. Our results reflect the importance of the environment salt composition and how this can modify the microbial physiological state.