Most of the known species inhabit the digestive tracts of animals and serve as symbionts (Wolinella spp.

However, numerous environmental sequences and isolates of Campylobacteria have been recovered from hydrothermal vents and cold seep habitats.

[6] A member of the phylum Campylobacterota occurs as an endosymbiont in the large gills of the deepwater sea snail Alviniconcha hessleri.

[8] The Campylobacteria 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.

[9] Autotrophic Campylobacteria use the reverse Krebs cycle to fix carbon dioxide into biomass, a pathway originally thought to be of little environmental significance.