The Helicobacter pylori CrdRS two-component regulation system (HP1364/HP1365) is required for copper-mediated induction of the copper resistance determinant CrdA

The CrdRS (HP1365-HP1364) two-component system is not involved in ph-responsive gene regulation in the Helicobacter pylori Strains 26695 and G27

The human gastric pathogen Helicobacter pylori is extremely well adapted to the highly acidic conditions encountered in the stomach. The pronounced acid resistance of H. pylori relies mainly on the ammonia-producing enzyme urease. However, urease-independent mechanisms are likely to contribute to acid adaptation. pH-responsive gene regulation in this organism is mediated by a two-component system (HP0166-HP0165) designated ArsRS and the metal-dependent regulators NikR and Fur. Recently, it was reported that another two-component system termed CrdRS (HP1365-HP1364) is required for pH-responsive regulation of the major acid-resistance systems in the H. pylori strain J99. By the analysis of crdRS null mutants of the H. pylori strains 26695 and G27, we show that low pH induction of both the urease and the amidase genes occurs in the absence of crdRS in these strains, suggesting substantial strain-specific differences in the regulation of a major virulence determinant.

The orphan response regulator HP1021 of Helicobacter pylori regulates transcription of a gene cluster presumably involved in acetone metabolism

Helicobacter pylori is a gastric pathogen for which no nonhuman reservoir is known. In accordance with the tight adaptation to its unique habitat, the human stomach, H. pylori is endowed with a very restricted repertoire of regulatory proteins. Nevertheless, the three complete two-component systems of H. pylori were shown to be involved in the regulation of important virulence traits like motility and acid resistance and in the control of metal homeostasis. HP1021 is an orphan response regulator with an atypical receiver domain whose inactivation has a considerable impact on the growth of H. pylori. Here we report the identification of HP1021-regulated genes by whole-genome transcriptional profiling. We show that the transcription of the essential housekeeping genes nifS and nifU, which are required for the assembly of Fe-S clusters, is activated by HP1021. Furthermore, we demonstrate that the expression of a gene cluster comprising open reading frames hp0690 to hp0693 and hp0695 to hp0697 which is probably involved in acetone metabolism is strongly upregulated by HP1021. Evidence is provided for a direct regulation of the hp0695-to-hp0697 operon by the binding of HP1021 to its promoter region.

Global analysis of two-component gene regulation in H. pylori by mutation analysis and transcriptional profiling

The human gastric pathogen Helicobacter pylori was among the first microorganisms whose genome sequence was determined. It has a remarkably small repertoire of two-component regulators comprising three histidine kinases and five response regulators involved in transcriptional regulators as well as a bifunctional histidine kinase and four response regulators which build up the chemotaxis regulatory system. However, the two-component systems of H. pylori proved to play an important role for both in vitro growth of the organism and its ability to colonize its host. Here, we describe the experimental approaches applied to characterize the two-component systems of H. pylori, which were mostly based on the availability of the H. pylori genome sequence. These approaches comprise conventional techniques including mutation analysis as well as sophisticated methods like whole genome transcriptional profiling.

Iron-responsive repression of urease expression in Helicobacter hepaticus is mediated by the transcriptional regulator Fur

Persistent colonization of mucosal surfaces by bacteria in the mammalian host requires concerted expression of colonization factors, depending on the environmental conditions. Helicobacter hepaticus is a urease-positive pathogen that colonizes the intestinal and hepatobiliary tracts of rodents. Here it is reported that urease expression of H. hepaticus is iron repressed by the transcriptional regulator Fur. Iron restriction of growth medium resulted in a doubling of urease activity in wild-type H. hepaticus strain ATCC 51449 and was accompanied by increased levels of urease subunit proteins and ureA mRNA. Insertional inactivation of the fur gene abolished iron-responsive repression of urease activity, whereas inactivation of the perR gene did not affect iron-responsive regulation of urease activity. The iron-responsive promoter element was identified directly upstream of the H. hepaticus ureA gene. Recombinant H. hepaticus Fur protein bound to this ureA promoter region in a metal-dependent matter, and binding resulted in the protection of a 41-bp, Fur box-containing operator sequence located at positions -35 to -75 upstream of the transcription start site. In conclusion, H. hepaticus Fur controls urease expression at the transcriptional level in response to iron availability. This represents a novel type of urease regulation in ureolytic bacteria and extends the already diverse regulatory repertoire of the Fur protein.

NikR mediates nickel-responsive transcriptional repression of the Helicobacter pylori outer membrane proteins FecA3 (HP1400) and FrpB4 (HP1512)

The transition metal nickel plays an important role in gastric colonization and persistence of the important human pathogen Helicobacter pylori, as it is the cofactor of the abundantly produced acid resistance factor urease. Nickel uptake through the inner membrane is mediated by the NixA protein, and the expression of NixA is controlled by the NikR regulatory protein. Here we report that NikR also controls the nickel-responsive expression of the FecA3 (HP1400) and FrpB4 (HP1512) outer membrane proteins (OMPs), as well as the nickel-responsive expression of an ExbB-ExbD-TonB system, which may function in energization of outer membrane transport. Transcription and expression of the frpB4 and fecA3 genes were repressed by nickel in wild-type H. pylori 26695, but they were independent of nickel and derepressed in an isogenic nikR mutant. Both the frpB4 and fecA3 genes were transcribed from a promoter directly upstream of their start codon. Regulation by NikR was mediated via nickel-dependent binding to specific operators overlapping either the +1 or -10 sequence in the frpB4 and fecA3 promoters, respectively, and these operators contained sequences resembling the proposed H. pylori NikR recognition sequence (TATWATT-N(11)-AATWATA). Transcription of the HP1339-1340-1341 operon encoding the ExbB2-ExbD2-TonB2 complex was also regulated by nickel and NikR, but not by Fur and iron. In conclusion, H. pylori NikR controls nickel-responsive expression of the HP1400 (FecA3) and HP1512 (FrpB4) OMPs. We hypothesize that these two NikR-regulated OMPs may participate in the uptake of complexed nickel ions and that this process is energized by the NikR-regulated ExbB2-ExbD2-TonB2 system, another example of the specific adaptation of H. pylori to the gastric lifestyle.

The novel Helicobacter pylori CznABC metal efflux pump is required for cadmium, zinc, and nickel resistance, urease modulation, and gastric colonization

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.

Requirement of histidine kinases HP0165 and HP1364 for acid resistance in Helicobacter pylori

In this study, we investigated a potential requirement of two-component signal transduction systems for acid resistance in Helicobacter pylori. In comparison to a wild-type strain, isogenic strains with null mutations in either HP0165 or HP1364 histidine kinases were impaired in their ability to grow at pH 5.0. The growth of complemented mutant strains was similar to that of the wild-type strain. H. pylori DNA array analyses and transcriptional reporter assays indicated that acid-responsive gene transcription was altered in the HP0165 and HP1364 null mutant strains compared to the parental wild-type strain. These results indicate that intact HP0165 and HP1364 histidine kinases are required for acid resistance in H. pylori.

Regulation of expression of atypical orphan response regulators of Helicobacter pylori

The human gastric pathogen Helicobacter pylori exhibits a remarkably small repertoire of transcriptional regulators including three complete two-component systems as well as the orphan response regulators HP1021 and HP1043. Both HP1021 and HP1043 show atypical receiver sequences and are required for the normal cell growth of H. pylori. Recently, we demonstrated that phosphorylation of HP1021 and HP1043 according to the two-component paradigm is not a prerequisite for the cell growth-associated functions of these response regulators, raising the question of how the activity of this regulatory proteins is modulated. Here, we report that strict transcriptional control of its expression is not involved in the cell-growth associated function of HP1021. We show that expression of hp1043 is controlled both on the post-transcriptional or post-translational level and by transcriptional regulation. Furthermore, we provide evidence that hp1043 can be replaced by the orthologous gene cj0355 from Campylobacter jejuni.

Crystallization and preliminary X-ray crystallographic study of HP1043, a Helicobacter pylori orphan response regulator

The HP1043 protein of Helicobacter pylori is related to the two-component system that regulates prokaryotic transcription in response to environmental changes. The HP1043 gene encodes an orphan response regulator (RR). The N-terminal domain of HP1043 (HP1043N) was purified by affinity-column chromatography. The purified protein was crystallized by hanging drop vapor diffusion at 293 K. The crystal belongs to primitive orthorhombic space group P2(1)2(1)2 with cell dimensions of a=89.0, b=41.3, and c=31.7 A. Assuming the presence of one molecule per asymmetric unit, the solvent content was estimated to be about 45%. A complete data set was collected at 1.8 A resolution.