This consideration is in agreement with the observation

that zin T is constitutively expressed in a znu A mutant strain, but that ZnuA accumulation is not significantly modulated by the absence of zin T (Figure 5). check details This is likely explained by a decrease of the zinc concentration in the cytoplasm in the absence of ZnuA, but not of ZinT, with the consequent derepression of zin T by Zur. It should be highlighted that the zin T mutant strain exhibits a sharp growth defect either in LB supplemented with 0.5 mM EDTA or in defined medium. This behaviour was not observed in a zin T mutant of S. enterica [18], which showed a clear impairment of growth in LB only in presence of 2 mM EDTA, a concentration at which the E. coli O157:H7 mutant is hardly able to grow. Furthermore, our results indicate that there are differences between E. coli O157:H7 and S. enterica in the regulation of znu A and zin T in response to low zinc availability (Figure 4). In particular, Selleckchem JNK inhibitor in E. coli O157:H7 ZinT can be easily detected in bacteria growing in a medium supplemented with up to 1 μM zinc, whereas in S. enterica this protein accumulates only in media completely devoid of the metal. This observation, which is in agreement with the different effect of zin T disruption in the

two bacterial species, may suggest that the relative role of ZnuA and ZinT could be slightly different in the two microorganisms. Although several of the bacteria which rely on the ZnuABC transporter to import zinc do not possess of ZinT [18], our study suggests that, despite the role of ZinT is clearly dependent on the presence of ZnuA, its contribution to metal recruitment within the periplasmic space is considerable. The exact involvement of ZinT in zinc uptake is yet to be determined, but it is possible to hypothesize that ZinT and ZnuA display a diverse ability to sequester metal ions from different molecules within the periplasm or that the binding of ZinT to ZnuA accelerates the rate of metal transfer to

ZnuB [18]. We have also analyzed the involvement of the zinc uptake system in the interaction between E. coli O157:H7 and epithelial Caco-2 cells. Both ZnuA and ZinT accumulates at high levels in bacteria adhering to the cell monolayer, but not in bacteria cultivated in D-MEM without cells (Figure 9). This finding expands previous observations showing that bacterial pathogens have to face with a problem of zinc paucity within the host [17] and specifically suggests that the host cell surface microenvironment is poor of zinc, possibly due to active metal sequestration mechanism implemented by eukaryotic cells. In line with this observation strains lacking znu A display a reduced ability to adhere to epithelial cells (Table 4).