The fdxA Ferredoxin Gene Can Down-Regulate frxA Nitroreductase Gene Expression and Is Essential in Many Strains of Helicobacter pylori

Abstract

Very few examples of metabolic regulation are known in the gastric pathogen Helicobacter pylori. An unanticipated case was suggested, however, upon finding two types of metronidazole (Mtz)-susceptible strains: type I, in which frxA (which encodes a nitroreductase that contributes to Mtz susceptibility) is quiescent, and type II, in which frxA is well expressed. Here we report that inactivation of the fdxA ferredoxin gene (hp277) in type I strains resulted in high-level frxA expression (in effect, making them type II). However, fdxA null derivatives were obtained from only 6 of 32 type I strains tested that were readily transformed with an frxA::aphA marker. This suggested that fdxA is often essential. This essentiality was overcome in 4 of 20 strains by inactivating frxA, which suggested both that frxA overexpression is potentially deleterious and also that fdxA has additional, often vital roles. With type II strains, in contrast, fdxA null derivatives were obtained in 20 of 23 cases tested. Thus, fdxA is dispensable in most strains that normally exhibit (and tolerate) strong frxA expression. We propose that restraint of frxA expression helps maintain balanced metabolic networks in most type I strains, that other homeostatic mechanisms predominate in type II strains, and that these complex results constitute a phenotypic manifestation of H. pylori's great genetic diversity.

Helicobacter acinonychis : Genetic and Rodent Infection Studies of a Helicobacter pylori -Like Gastric Pathogen of Cheetahs and Other Big Cats

“…Five mouse-adapted strains of H. pylori were used here: SS1 (31,36); X47 (also known as X47-2AL [2,15]); 88-3887, a close relative of strain 26695 (24,27,34), whose genome has been fully sequenced (47); and AM1 from India and AL10103 from Alaska (D. Dailidiene, A. K. Mukhopadhyay, M. Zhang, and D. E. Berg, unpublished data).…”

“…Two of the six Ohio zoo isolates and three European circus isolates were MTZ sensitive (MIC ϭ 1.5 g of MTZ/ml [or in one case, 3 g of MTZ/ml]), and the other five isolates were moderately or highly resistant (MIC range from 8 to 128 g of MTZ/ml) ( Table 3). Two types of Mtz s H. pylori are known and can be distinguished by the ease of mutation to resistance: type I requires inactivation of just the rdxA nitroreductase gene (because the related frxA gene is quiescent), and type II requires inactivation of both rdxA and frxA (26,34). The three mouse-colonizing strains of H. pylori characterized to date (SS1, X47, and 88-3887) are each type II (26,34 , with MTZ MICs of 32 and 16 g per ml in group I and II strains, respectively ( Table 3), suggesting that the frxA nitroreductase gene is either quiescent or absent from these strains.…”

“…Two types of Mtz s H. pylori are known and can be distinguished by the ease of mutation to resistance: type I requires inactivation of just the rdxA nitroreductase gene (because the related frxA gene is quiescent), and type II requires inactivation of both rdxA and frxA (26,34). The three mouse-colonizing strains of H. pylori characterized to date (SS1, X47, and 88-3887) are each type II (26,34 , with MTZ MICs of 32 and 16 g per ml in group I and II strains, respectively ( Table 3), suggesting that the frxA nitroreductase gene is either quiescent or absent from these strains. The small differences in MICs were reproducible and suggested quantitative differences in parameters such as basal levels of other nitroreductases, of MTZ uptake, or of repair of MTZ-induced DNA damage (see references 26 and 34).…”

HP0902 from Helicobacter pylori is a thermostable, dimeric protein belonging to an all-β topology of the cupin superfamily

“…The HP0902 protein was identified as one of the 13 proteins that are probably secreted by H. pylori. In another study, HP0902 was identified as one of the over-expressed proteins in a mutant strain of H. pylori lacking the fdxA gene, which regulates the resistance of H. pylori to the antibiotic metronidazole (30,31). Thus, we expect that our structural genomics study on HP0902 would ultimately facilitate the functional identification of the protein, thereby contributing to the understanding of the mechanisms underlying the pathogenicity and resistance behaviors of H. pylori.…”

Virulence Genes and Neutral DNA Markers ofHelicobacter pyloriIsolates from Different Ethnic Communities of West Bengal, India

“…This pattern suggests selection for proteins with different structures, functions, or antigenic properties during different infections. The genetic diversity of H. pylori is postulated to reflect numerous factors: mutation (44), recombination between divergent lineages (42), selection based on differences among human hosts in traits that may be important to individual strains (14), and finally its non-epidemic (preferentially intrafamilial) mode of transmission, which lowers the chance of selection for any one or a few possibly most fit genotypes (13,29). Clinical isolates from adults are also likely to have diverged genetically from strains that may have infected them years before (in infancy), the result of years of selection for derivatives that are better adapted to the particular person, coupled with changes in gastric physiology over time.…”