https://en.m.wikipedia.org/wiki/Campylobacterota

Numerous environmental sequences and isolates of Campylobacterota have also been recovered from hydrothermal vents and cold seep habitats. Examples of isolates include Sulfurimonas autotrophica, Sulfurimonas paralvinellae, Sulfurovum lithotrophicum and Nautilia profundicola. A member of the phylum Campylobacterota occurs as an endosymbiont in the large gills of the deepwater sea snail Alviniconcha hessleri.

The Campylobacterota found at deep-sea hydrothermal vents characteristically exhibit chemolithotrophy, meeting their energy needs by oxidizing reduced sulfur, formate, or hydrogen coupled to the reduction of nitrate or oxygen. Autotrophic Campylobacterota use the reverse Krebs cycle to fix carbon dioxide into biomass, a pathway originally thought to be of little environmental significance. The oxygen sensitivity of this pathway is consistent with their microaerophilic or anaerobic niche in these environments, and their likely evolution in the Mesoproterozoic oceans, which are thought to have been sulfidic with low levels of oxygen available from cyanobacterial photosynthesis.

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Gammaproteobacteria and Riftia pachyptila switch from the Calvin-Benson cycle to the rTCA cycle in response to concentrations of H2S.

Physiological responsesEdit

Activation of the H2 receptor results in the following physiological responses:

Stimulation of gastric acid secretion (Target of anti-histaminergics (H2 receptors) for peptic ulcer disease and GERD)

Inhibit antibody synthesis, T-cell proliferation and cytokine production

Smooth muscle relaxation (Experimental histamine H2 receptor agonist used for asthma and COPD)