Abstract
Maintaining
metal homeostasis is crucial for the adaptation of
Helicobacter
pylori
to the gastric environment. Iron, copper, and nickel
homeostasis has recently been demonstrated to be required for the
establishment of
H. pylori
infection in animal models. Here we
demonstrate that the HP0969-0971 gene cluster encoding the Czc-type
metal export pump homologs HP0969, HP0970, and the
H.
pylori
-specific protein HP0971 forms part of a novel
H.
pylori
metal resistance determinant, which is required for gastric
colonization and for the modulation of urease activity. Insertional
mutagenesis of the HP0971, HP0970, or HP0969 genes in
H.
pylori
reference strain 26695 resulted in increased sensitivity to
cadmium, zinc, and nickel (czn), suggesting that the encoded proteins
constitute a metal-specific export pump. Accordingly, the genes were
designated
cznC
(HP0971),
cznB
(HP0970), and
cznA
(HP0969). The CznC and CznA proteins play a predominant
role in nickel homeostasis, since only the
cznC
and
cznA
mutants but not the
cznB
mutant displayed an 8-
to 10-fold increase in urease activity. Nickel-specific affinity
chromatography demonstrated that recombinant versions of CznC and CznB
can bind to nickel and that the purified CznB protein interacted with
cadmium and zinc, since both metals competitively inhibited nickel
binding. Finally, single
cznA
,
cznB
, and
cznC
mutants did not colonize the stomach in a Mongolian
gerbil-based animal model. This demonstrates that the metal export
functions of
H. pylori cznABC
are essential for gastric
colonization and underlines the extraordinary importance of metal ion
homeostasis for the survival of
H. pylori
in the gastric
environment.