Figure 1.

Bayesian phylogeny of the B. cereus group SR1 homologues. Our phylogeny suggests that the ancestral gene encoding SR1P was duplicated twice in the ancestor of the B. cereus group Bacilli. The first duplication generated copy III and an ancestral sequence for copies I and II. In the second duplication this ancestral sequence was duplicated once more to give rise to the copies I and II. All three copies were retained in subsequent speciation events through which the species of the B. cereus group were generated, except for the third copy in B. cytotoxicus, which was lost.