Both BAPS and fineSTRUCTURE analysis revealed the absence of DNA exchange between Clade 1 and the other clades, indicating a possible sexual isolation of Lp serogroups from other Legionella species. To understand the nature of recombination predicted by ClonalFrame analysis, we tried to assign the origin of each event by a BLASTN pipeline described in Methods. However, recombinant sequences could not be matched to a particular ancestor in any other Legionella species.