From Bathtubs to Bloodfeeders: An Evolutionary Study of the Aphaproteobacterial Gellertiella (formerly Ca. Reichenowia)

Many leeches are blood feeders and host bacteria within specialized organs. One example is Placobdella which hosts the alpha-proteobacterial Candidatus Reichenowia. It is assumed that Reichenowia provisions Placobdella with B vitamins. Although Reichenowia consistently places within Rhizobiaceae, its free-living relative remains a mystery. By obtaining genome sequences of the endosymbiotic bacteria of six species of Placobdella, I address questions regarding the role of Reichenowia and its origin. B vitamin synthesis pathways remain largely intact across all taxa with many gaps likely representing a lack of knowledge concerning alternate synthesis routes. I find robust and consistent support for the nesting of the free-living Gellertiella hungarica within Reichenowia, necessitating the dissolution of Reichenowia. The topology of this clade suggests two independent origins of endosymbiosis from a G. hungarica-like ancestor. These findings clarify the ecology of the system and point towards a potentially novel model system for investigating the early stages of endosymbiosis.M.Sc