Nonpathogenic Epsilonproteobacteria

AbstractThe Epsilonproteobacteria is a class within the phylum Proteobacteria and has been primarily recognized as a group of pathogenic microorganisms. However, nonpathogenic Epsilonproteobacteria has been increasingly of great biological importance. They represent bacteria with the highest metabolic versatility. Nonpathogenic Epsilonproteobacteria occurs dominantly in various redoxclines such as deep‐sea vents, stratified ocean, terrestrial sulfidic caves, and oil fields as both epi‐ or endosymbionts and free‐living microorganisms. Recent genome analysis has revealed that some virulence determinants and the genomic plasticity of the pathogenic Epsilonproteobacteria appear to have roots in nonpathogenic, chemoautotrophic Epsilonproteobacteria. These work advantageously for pathogenic Epsilonproteobacteria to be efficiently and persistently infectious and for nonpathogenic Epsilonproteobacteria to thrive in extreme habitats. In the genomic era, previously unrecognized evolutionary links are emerging between important human/animal pathogens and their nonpathogenic, symbiotic, chemoautotrophic relatives.Key conceptsThe Epsilonproteobacteria is the class within the phylum Proteobacteria and represented by important human/animal pathogens.The perception of the class Epsilonproteobacteria has recently changed dramatically.The Epsilonproteobacteria comprise numerous nonpathogenic bacteria with diverse ecophysiology and phylogeny.Nonpathogenic Epsilonproteobacteria play key roles in biogeochemical cycles in various extreme environments on earth.Nonpathogenic Epsilonproteobacteria provide new insights into the origin of animal/human pathogens.