5% (w/v) agar. For growth under metal limiting conditions a modified M9 minimal medium, hereafter named modM9 (43 mM Na2HPO4, 22 mM KH2PO4, 19 mM NH4Cl, 1 mM MgSO4, 0.1 mM CaCl2 and 0.2% glucose) was used. To prepare the modM9, as well as other zinc-free solutions, we used ultra-pure water produced by a reverse osmosis system characterized by conductivity lower than

0.03 μS/cm. Moreover, bacterial culture and all solutions used with modM9 were prepared and incubated using zinc-free polypropylene plasticware (Falcon 50 and 10 ml tubes, Gilson tips and Eppendorf microtubes) avoiding glassware Luminespib manufacturer and other uncontrolled materials, except the

96-well plates used for the growth curves in modM9 which were in polystyrene. In this case, to remove metal contaminants of microtiter plates were treated overnight with 10 μM EDTA and then washed three times with fresh modM9 to eliminate EDTA traces. The effective ability of this procedure in removing zinc traces was evaluated by measuring the emission spectra of the final washing solution after check details the addition of 25 μM Zinquin, a highly specific Zn-fluorophore [17]. When required, the culture media were supplemented with the appropriate antibiotics (ampicillin 100 μg/ml, kanamycin 50 μg/ml, chloramphenicol 15 μg/ml). Mutant strains construction All E. coli O157:H7 knockout mutants and the 3xFLAG strains were obtained following the protocol described by Datsenko Parvulin and Wanner [28] and the epitope tagging method described by Uzzau et al. [29], respectively. The plasmids and the oligonucleotides used for mutants’ construction are listed in Table 2 and 3, respectively. Recombinant strains were selected on chloramphenicol or kanamycin

LB plates and confirmed by PCR using oligonucleotides internal to the chloramphenicol or kanamycin resistance cassettes in combination with primers specific for each gene. Table 2 Plasmids Plasmid Relevant genotype or characteristic Reference or source pKD46 lambda red recombinase function Datsenko and Wanner, 2000 pKD3 chloramphenicol resistance cassette template Datsenko and Wanner, 2000 pKD4 kanamycin resistance cassette template Datsenko and Wanner, 2000 pSUB11 INK 128 purchase 3xFLAG-kanamycin resistance cassette template Uzzau et al., 2001 p18ZnuAO157 ZnuA of E. coli O157:H7 cloned in pEMBL18 This work p18ZnuA E. coli ZnuA of E.