LysRS2 gene tree. Maximum likelihood phylogenetic tree for 177 bacterial and 6 archaeal LysRS2 sequences, colored green and black, respectively. The tree has been rooted using four AspRS sequences (B. aphidicoda, E. coli, C. jejuni, T. maritima). Bootstrap percentage values greater than 50% are indicated. Arrows indicate plausible paths for LGT events. Question marks indicate considerable uncertainties as to the origin of the LGT. Clamidiae (6) refers to 6 species specified in SM, additional file 1. Methanosarcina (3) refers to Methanosarcina acetivorans, Methanosarcina mazei, Methanosarcina barkeri. B (55) refers to 55 bacterial species: 3 Clostridia, 26 Bacilli, 13 Molicutes, 1 Fusobacteria, 2 Clostridia, 3 Bacteroidestes, 6 Chlorobia and 1 Spirochaetae. B (3) refers to the following 3 bacterial species: Solibacter usitatus, Anaeromyxobacter dehalogenans, Symbiobacterium thermophilum The species included in the groups Cyanobacteria (9), Actinobacteria (15) and Proteobacteria (80) are provided as Supplementary Material, additional file 1. Listing of the bacterial and archaeal phyla, classes and species, with corresponding LysRS2 accession numbers and their sources are also provided in SM, additional file 1. The complete (unabbreviated) LysRS2 ML trees are given as SM, additional file 3.