Figure 1.

Schematic summarizing the key genetic, ecological, and evolutionary factors known to influence the transition of Helicobacter pylori along the parasitism–mutualism continuum. Factors known to increase potential pathogenicity are in red, those that are involved in colonization and survival in the human host, but which have no direct evidence of conferring either cost or benefit to the host are in black, and factors that are thought to be associated with conferred benefits to the host (either directly or indirectly) are in green. Further factors that are predicted from theory but which have not been examined empirically are included in italics. Details of each association are discussed within the main text. References: (1) Oleastro and Ménard (2013); (2) Censini et al. (1996); (3) Maeda et al. (1998); (4) Persson et al. (2011); (5) Kodaman et al. (2014); (6) Gaddy et al. (2013); (7) Atherton et al. (1996); (8) León-Barúa et al. (2006); (9) Anderson and May (1982); (10) Eaton et al. (1992); (11) Ottemann and Lowenthal (2002); (12) Tsuda et al. (1994); (13) Gobert et al. (2001); (14) Bonis et al. (2010); (15) Salama et al. (2013); (16) Chen and Blaser (2007); (17) Arnold et al. (2011).