One of the principal findings of our work is that Legionella phylogeny resolve into four distinct clades based, in general, on human host-virulence demarcations (Fig. 1A). The obvious question to ask is, what are the genetic features that distinguish these groups of species? Clade 1 comprises only the Lp serogroups, which are responsible for approximately 92% of LD cases. Clade 2 are rarely associated with human disease while Clade 3 species are associated with LD and Pontiac Fever with L. longbeachae causing ~30% of LD cases in Australia and New Zealand. Clade 4 contains the only legionella-like amoebal pathogen (LLAP) species in the database, L. rowbothamii, which is associated with co-infection with other pathogens and is unlikely to be the sole causative organism in human disease. We did not find evidence to suggest adaptation through acquisition of known metabolic pathways. However, the function of many accessory genes is unattributed at this time, so we may be missing some of the picture through our partial existing knowledge.