Host-dependent activation of IS1203v excision in shiga toxin-producing Escherichia coli

Abstract IS 1203 v is an insertion sequence (IS) which is identical to the most abundant IS elements in the genome of Escherichia coli O157:H7. However, there is no sequence homologous to IS 1203 v in the genome of E. coli K-12. We constructed a system to analyze the excision frequency of IS 1203 v, and demonstrated that the frequency in E. coli O157:H7 was approximately 10 5 times higher than that in E. coli K-12. We also investigated the excision frequencies of IS 1203 v in various E. coli isolates, and showed that the excision frequencies of IS 1203 v-possessing strains were approximately 10 3 times higher than those of IS 1203 v-nonpossessing strains. The results suggest that the IS 1203 v-possessing strains use a common system to enhance IS 1203 v excision.