Carbon Fixation Driven by Molecular Hydrogen Results in Chemolithoautotrophically Enhanced Growth of Helicobacter pylori

Abstract

A molecular hydrogen (H 2 )-stimulated, chemolithoautotrophic growth mode for the gastric pathogen Helicobacter pylori is reported. In a culture medium containing peptides and amino acids, H 2 -supplied cells consistently achieved 40 to 60% greater growth yield in 16 h and accumulated 3-fold more carbon from [ 14 C]bicarbonate (on a per cell basis) in a 10-h period than cells without H 2 . Global proteomic comparisons of cells supplied with different atmospheric conditions revealed that addition of H 2 led to increased amounts of hydrogenase and the biotin carboxylase subunit of acetyl coenzyme A (acetyl-CoA) carboxylase (ACC), as well as other proteins involved in various cellular functions, including amino acid metabolism, heme synthesis, or protein degradation. In agreement with this result, H 2 -supplied cells contained 3-fold more ACC activity than cells without H 2 . Other possible carbon dioxide (CO 2 ) fixation enzymes were not up-expressed under the H 2 -containing atmosphere. As the gastric mucus is limited in carbon and energy sources and the bacterium lacks mucinase, this new growth mode may contribute to the persistence of the pathogen in vivo. This is the first time that chemolithoautotrophic growth is described for a pathogen. IMPORTANCEMany pathogens must survive within host areas that are poorly supplied with carbon and energy sources, and the gastric pathogen Helicobacter pylori resides almost exclusively in the nutritionally stringent mucus barrier of its host. Although this bacterium is already known to be highly adaptable to gastric niches, a new aspect of its metabolic flexibility, whereby molecular hydrogen use (energy) is coupled to carbon dioxide fixation (carbon acquisition) via a described carbon fixation enzyme, is shown here. This growth mode, which supplements heterotrophy, is termed chemolithoautotrophy and has not been previously reported for a pathogen. Helicobacter pylori is the causative agent of gastric ulcers and chronic gastritis (1). It infects about 50% of the world population (2), and if the infection persists without treatment, it can lead to the development of gastric cancers (3). H. pylori inhabits the gastric mucosa, an environment in which energy and carbon sources are limited. Most of the colonizing organisms within the host stomach are not associated with gastric epithelial cells; rather, they are found in the mucosa, where oxidizable carbon substrates are known to be scarce (4, 5). While the highly diverse glycans present in mucus can be accessed by certain microbiota (6), this requires specialized enzymes that seem to be lacking in Helicobacter species (7). Furthermore, the bacterium lacks a mucinase that would liberate utilizable substrates (8). Still, H. pylori seems to thrive in the mucosal environment, achieving typical viable numbers of 10 2 to 10 4 CFU per g or ml of stomach mucus (9). Carbon sources usable by H. pylori include small organic acids, amino acids, and peptides (8, 10-13), but the extent of this metabolism in vivo is not well understood...

Diagnostic of Helicobacter pylori infection

“…The presence of hydrogen (H 2 ) in the incubation atmosphere also achieved 40%–60% greater growth yield in another study . They could show that the addition of H 2 increased the amount of several enzymes: hydrogenase, the biotin carboxylase subunit of acetyl‐CoA carboxylase and others.…”

“…16 The presence of hydrogen (H 2 ) in the incubation atmosphere also achieved 40%-60% greater growth yield in another study. 17 They could show that the addition of H 2 increased the amount of several enzymes: hydrogenase, the biotin carboxylase subunit of acetyl-CoA carboxylase and others. The authors claimed that, for the first time, a chemolithoautotrophic growth was described for a pathogen, and this may contribute to the persistence of the pathogen in vivo.…”

Diagnosis of Helicobacter pylori infection

“…Proteomic comparisons showed increased amounts of proteins such as hydrogenase and acetyl coenzyme A carboxylase. This growth characteristic may contribute to the persistence of the pathogen in vivo as the gastric mucus is limited in carbon and energy sources . MALDI‐TOF mass spectrometry was confirmed to have low efficiency to identify H. pylori…”

“…This growth characteristic may contribute to the persistence of the pathogen in vivo as the gastric mucus is limited in carbon and energy sources. 13 MALDI-TOF mass spectrometry was confirmed to have low efficiency to identify H. pylori. 14 The current recommendation for histology staining is to use immunohistochemistry (IHC) stains only in the case of non-active chronic gastritis.…”

“…34 The molecular methods applied for genotyping were 1) macroarrays to explore the polymorphism for two genes: hopA and glmM: two patients suffered from relapses 1 and 3 years after H. pylori treatment, while the third was a reinfection, 35 2) RAPD-PCR applied in 2 studies to explore: 1, H. pylori transmission in families using fecal samples, it was shown that mother-to-child was the main route of transmission, 36 and 2, genetic variability in Colombia showing that it was greater in the high risk population of gastric cancer. 37 13 C-UBT remains one of the best methods to diagnose H. pylori infection. A limit is the need to stop PPI administration during the 2 weeks preceding the test.…”