One of the reasons of this difficulty is that many toxins used for classification are encoded on MGEs that have HGT potential, e.g. plasmids or transposons [3, 36, 37]. Cereulide may cause severe and potential lethal infection during

an “”emetic”" form of B. cereus food poisoning. Most emetic B. cereus strains belong to a homogeneous group of B. cereus sensu stricto. Although rare, the emetic B. weihenstephanensis strains were recently isolated in nature [13]. Furthermore, a heat stable toxin, structural related to cereulide, has also been found in Paenibacillus tundra strain [38]. As a consequence, the intra- and inter-species diversity and potential click here transmission of the cereulide biosynthetic gene cluster is therefore thought provoking. In this study, the sequence diversity of emetic B. cereus sensu stricto and B. weihenstephanensis was analyzed. Since emetic B. cereus sensu stricto had been found to be restricted to a homogeneous group [30], only two B. cereus sensu stricto isolates were analyzed and compared the other five known B. weihenstephanensis. Except for AH187, the unfinished gapped genome sequences of the other emetic isolates were recently submitted [39]. As expected, the two emetic B. cereus sensu stricto isolates share very similar gene content in genome level. Furthermore, their “”ces”" plasmids are quite coherent in terms of synteny, learn more protein

similarity and gene content. Compared to AH187, IS075 has a larger plasmid pool, of which the “”ces”" plasmid is pXO1-like, but the presence of a pXO2-like plasmid was also indicated [40]. Sequence diversity between B. cereus sensu stricto and B. weihenstephanensis or within B. weihenstephanensis was observed. It was also evidenced that the ces cluster had undergone horizontal gene transfer (HGT). This could be clued by the fact that the cluster

is present in different hosts (B. cereus sensu stricto vs. B. weihenstephanensis), which have different chromosomal background, and displays different genomic locations (plasmids vs. chromosome). Moreover, another striking indication for HGT was the presence of putative MGEs in all tested emetic strains. The composite transposon, Tnces, located on large plasmids (pMC67/pMC118) in two B. weihenstephanensis strains isolated from soil in Denmark Methane monooxygenase was identified. The mobility of Tnces was also proved by transposition experiments performed on a Tnces-derived element, indicating a HGT potential of the cereulide gene cluster in pMC67/pMC118. Although the ces gene cluster is not flanked by IS elements in the other two types of emetic isolates, a Group II intron carrying an endonuclease gene in AH187 and IS075, and a putative integrase/recombinase gene in CER057, CER074 and BtB2-4 were also observed downstream of cesD. Both Group II intron and recombinase can potentially be involved in genome dynamics.