Helicobacter pylori cadA encodes an essential Cd(II)-Zn(II)-Co(II) resistance factor influencing urease activity

Inactivation of Helicobacter pylori cadA, encoding a putative transition me tal ATPase, was only possible in one of four natural competent H. pylori st rains, designated 69A. All tested cadA mutants showed increased growth sens itivity to Cd(ll) and Zn(ll). In addition, some of them showed both reduced Ni-63 accumulation during growth and no or impaired urease activity, which was not due to lack of urease enzyme subunits. Gene complementation experi ments with plasmid (pY178)-derived H. pylori cadA failed to correct the def iciencies, whereas resistance to Cd(ll) and Zn(ll) was restored. Moreover, pY178 conferred increased Co(ll) resistance to both the cadA mutants and th e wild-type strain 69A. Heterologous expression of H. pylori cadA in an Esc herichia coli zntA mutant resulted in an elevated resistance to Cd(ll) and Zn(ll). Expression of cadA in E. coli SE5000 harbouring H. pylori nixA, whi ch encodes a divalent cation importer along with the H. pylori urease gene cluster, led to about a three-fold increase in urease activity compared wit h E. coli control cells lacking the H, pylori cadA gene. These results sugg est that H. pylori CadA is an essential resistance pump with ion specificit y towards Cd(ll), Zn(ll) and Co(ll). They also point to a possible role of H. pylori CadA in high-level activity of H. pylori urease, an enzyme sensit ive to a variety of metal ions.