Extensive diversity of Rickettsiales bacteria in two species of ticks from China and the evolution of the Rickettsiales

Background Bacteria of the order Rickettsiales (Alphaproteobacteria) are obligate intracellular parasites that infect species from virtually every major eukaryotic lineage. Several rickettsial genera harbor species that are significant emerging and re-emerging pathogens of humans. As species of Rickettsiales are associated with an extremely diverse host range, a better understanding of the historical associations between these bacteria and their hosts will provide important information on their evolutionary trajectories and, particularly, their potential emergence as pathogens.