Figure 4.

Maximum likelihood core genome phylogenetic tree of 103 spore-forming Bacillaceae, with indication of the number and type of spoVA operons present in the genomes, and proposed evolutionary scenarios. Three types of spoVA operons were identified in this analysis and are indicated in the tree. First, a spoVA¹ operon, encompassing spoVAA, spoVAB, spoVAC¹, spoVAD¹, spoVAEb¹, spoVAEa and spoVAF. Second, a spoVA² operon, encompassing a gene with a predicted DUF1657 domain, a gene with a YhcN/YljA domain, spoVAC², spoVAD², spoVAEb², a gene with a predicted DUF1657 domain and a gene with a predicted DUF 421 domain and DUF1657 domain. Third, a spoVA^2mob operon, which is a duplication of the spoVA² operon, but present on a mobile genetic element, e.g., Tn1546 in B. subtilis strains. The proposed evolutionary scenarios were based on protein trees of SpoVAC and SpoVAD and the genomic context of the spoVA operons. Strains of B. cereus, Geobacillus spp. and A. flavithermus all carry spoVA¹ and spoVA² operons. Six strains of B. cereus carry spoVA^2mob on a pXO1-like plasmid, as part of a Tn1546 transposon. Members of the B. subtilis group (B. subtilis, B. vallismortis, B. amyloliquefaciens, B. licheniformis) lost the spoVA² operon during evolution, but the spoVA^2mob operon re-entered in some strains as part of a Tn1546 transposon. Similarly, spoVA^2mob entered strains of B. thermoamylovorans and B. sporothermodurans. Incomplete spoVA¹ and spoVA² operons were observed in strains of B. thermoamylovorans, B. sporothermodurans and C. debilis.