No differences in growth were observed when bacteria were cultivated in LB, whereas the growth of all mutant strains decreased with 0.5 mM EDTA (Figure 1, panel A, data not shown for RG114) and even more with 2 mM EDTA treatment (data not shown). A recovery in growth of all mutant strains was observed upon supplementation of ZnSO4 to the LB containing EDTA. Figure 1 Growth curves.

BI 2536 concentration Panel A : growth curves of wild type (squares), Δ zin T:: kan (triangles) and Δ znu A:: kan (circles) in LB medium (close symbols), in LB supplemented with 0.5 mM EDTA (open symbols) and 0.2 mM ZnSO4 (dotted lines). Panel B : growth curves of the same strains in modM9 (close symbols) and in modM9 supplemented with 5 μM ZnSO4 (open symbols). In modM9 all mutant strains displayed a clear growth defect with respect to the wild type strain (Figure 1, panel B), with a major impairment of the growth of strains lacking znu A (RG114 data not shown) than that of the strain lacking only zin T. In this case, however, the addition of ZnSO4 to the culture medium significantly reduced the rate of growth Torin 1 cost of the wild type (Additional file 1 : Figure S1, panel A) and zin T mutant strains, likely due to toxic effects of the extracellular metal. In selleck compound contrast, a clear improvement in the growth of the strains

lacking znu A was observed upon the addition of zinc to the medium (Figure 1, panel B and Additional file 1 : Figure S1, panel B). The growth defect of the znu A mutant

strain was complemented by a multicopy plasmid overexpressing E. coli ZnuA, indicating that CYTH4 disruption of znu A does not abolish the functionality of the other genes of the znu ABC operon (Table 5 and Additional file 2 : Figure S2). The reduced rate of growth of the complemented strains is likely due to gene dosage effects, as previously described [17]. Table 5 Growth on LB plates Strainsa EDTA concentration   0 0.5 mM 1 mM 2 mM WT ++ ++ ++ ++ RG113 (Δ znuA :: kan) ++ +/- +/- – RG113 + p18ZnuAO157 ++ + + + RG113 + p18ZnuA E. coli ++ + + + a The strains were grown overnight in LB medium and then streaked on LB plates containing the indicated amounts of EDTA. Growth on agar plates was not modified by the presence or absence of antibiotics. Symbols : ++ growth, + weak growth, +/- weak growth of very small colonies, – no growth. ZinT and ZnuA expression studies The expression of zin T and znu A was indirectly analyzed by monitoring the proteins accumulation in strains which were modified by introducing the sequence encoding the 3xFLAG epitope at the 3′end of each gene (Figure 2). In agreement with previous studies [18, 21], also in E. coli O157:H7 cadmium and EDTA were able to induce the expression of ZinT and ZnuA. Moreover, ZnuA accumulation drastically decreased when bacteria were grown in 0.5 mM EDTA in presence of 0.2 mM ZnSO4, a quantity unable to saturate the binding ability of the chelator, whereas ZinT accumulation was only moderately affected.