SGI0, a relative of Salmonella genomic islands SGI1 and SGI2, lacking a class 1 integron, found in Proteus mirabilis

Abstract Several groups of integrative mobilizable elements (IMEs) have been found at the 3′-end of the chromosomal trmE gene, all harbouring a class 1 integron. Here, a new IME, Salmonella Genomic Island 0 (SGI0), was found in trmE in a French clinical Proteus mirabilis strain. SGI0 was characterized by the lack of class 1 integron. SGI0 is closely related to the backbones of SGI1 (97.59% nucleotide identity) and SGI2 (97.72% nucleotide identity). SGI0 harboured also the AcaCD binding sites and could be excised and completely lost in presence of an IncC plasmid as for SGI1. SGI1-V was also re-assessed. The SGI1-V backbone shared only 97.25% nucleotide identity with SGI1 and its class 1 integron is inserted in a different position to In104 in SGI1. Hence, SGI1-V should be considered to be independently derived and was re-named SGI-V. The SGI0 structure was a mosaic including segments from the SGI1, SGI2 and SGI1-V backbones, which suggests that recombination between these backbones is occurring. All of these SGIs, SGI0, SGI1, SGI2 and SGI-V independently arose from an original ancestor.