To clarify the evolutionary relationships and classification of
Bacillus
species, comprehensive phylogenomic and comparative analyses were performed on >300 Bacillus/Bacillaceae genomes. Multiple genomic-scale phylogenetic trees were initially reconstructed to identify different monophyletic clades of
Bacillus
species. In parallel, detailed analyses were performed on protein sequences of genomes to identify conserved signature indels (CSIs) that are specific for each of the identified clades. We show that in different reconstructed trees, most of the
Bacillus
species, in addition to the Subtilis and Cereus clades, consistently formed 17 novel distinct clades. Additionally, some
Bacillus
species reliably grouped with the genera Alkalicoccus, Caldalkalibacillus, Caldibacillus, Salibacterium and
Salisediminibacterium
. The distinctness of identified
Bacillus
species clades is independently strongly supported by 128 identified CSIs which are unique characteristics of these clades, providing reliable means for their demarcation. Based on the strong phylogenetic and molecular evidence, we are proposing that these 17
Bacillus
species clades should be recognized as novel genera, with the names Alteribacter gen. nov., Ectobacillus gen. nov., Evansella gen. nov., Ferdinandcohnia gen. nov., Gottfriedia gen. nov., Heyndrickxia gen. nov., Lederbergia gen. nov., Litchfieldia gen. nov., Margalitia gen. nov., Niallia gen. nov., Priestia gen. nov., Robertmurraya gen. nov., Rossellomorea gen. nov., Schinkia gen. nov., Siminovitchia gen. nov., Sutcliffiella gen. nov. and Weizmannia gen. nov. We also propose to transfer ‘
Bacillus kyonggiensi
s’ to Robertmurraya kyonggiensis sp. nov. (type strain: NB22=JCM 17569T=DSM 26768). Additionally, we report 31 CSIs that are unique characteristics of either the members of the Subtilis clade (containing the type species
B. subtilis
) or the Cereus clade (containing
B. anthracis
and
B. cereus
). As most
Bacillus
species which are not part of these two clades can now be assigned to other genera, we are proposing an emended description of the genus
Bacillus
to restrict it to only the members of the Subtilis and Cereus clades.
