Genomic Island 3 Is an Integrative and Conjugative Element and Contributes to Copper and Arsenic Tolerance of .

genomic island 3 (SGI3) was first described as a chromosomal island in 4,[5],12:i:-, a monophasic variant of subsp. serovar Typhimurium. The SGI3 DNA sequence detected from 4,[5],12:i:- isolated in Japan was identical to that of a previously reported one across entire length of 81 kb. SGI3 consists of 86 open reading frames, including a copper homeostasis and silver resistance island (CHASRI) and an arsenic tolerance operon, in addition to genes related to conjugative transfer and DNA replication or partitioning, suggesting that the island is a mobile genetic element. We successfully selected transconjugants that acquired SGI3 after filter-mating experiments using the serovars Typhimurium, Heidelberg, Hadar, Newport, Cerro, and Thompson as recipients. Southern blot analysis using I-CeuI-digested genomic DNA demonstrated that SGI3 was integrated into a chromosomal fragment of the transconjugants. PCR and sequencing analysis demonstrated that SGI3 was inserted into the 3' end of the tRNA genes or The length of the target site was 52 or 55 bp, and a 55-bp sequence indicating generation of the circular form of SGI3 was also detected. The transconjugants had a higher MIC against CuSO compared to the recipient strains under anaerobic conditions. Tolerance was defined by the gene cluster in the CHASRI. The transconjugants also had distinctly higher MICs against NaHAsO compared to recipient strains under aerobic conditions. These findings clearly demonstrate that SGI3 is an integrative and conjugative element and contributes to the copper and arsenic tolerance of .