Transposons Tn 1696 and Tn 21 and Their Integrons In4 and In2 Have Independent Origins

Abstract

The first 13.6 kb of the mercury and multidrug resistance transposon Tn1696, which includes the class 1 integron In4, has been sequenced. In4 is 8.33 kb long and contains the 5-conserved segment (5-CS) and 2.24 kb of the 3-conserved segment (3-CS) flanking four integrated cassettes. The 3-CS region is followed by one full copy and an adjacent partial copy of the insertion sequence IS6100 flanked, in inverse orientation, by two short segments (123 and 152 bp) from the outer right-hand end of class 1 integrons. This structure is representative of a distinct group of class 1 integrons that differs from In2, found in Tn21, and other related class 1 integrons. In4 does not include transposition genes but is bounded by characteristic 25-bp inverted repeats and flanked by a direct duplication of 5 bp of the target sequence, indicating that it was inserted by a transpositional mechanism. In4 lies between the resII and resI sites of a backbone mercury resistance transposon which is >99.5% identical to Tn5036. Although Tn21 and Tn1696 are both classified as members of the Tn21 subfamily of the Tn3 transposon family, the backbone mercury resistance transposons are only 79 to 96% identical. Tn21 also contains a region of about 0.7 kb not found in Tn1696. The integrons In2 and In4 carrying the antibiotic resistance genes have been inserted at different locations into distinct ancestral mercury resistance transposons. Thus, Tn21 and Tn1696 have independent histories and origins. Other transposons (Tn1403 and Tn1412) that include a class 1 integron also have independent origins. In all except Tn21, the integron is located within the res region of the backbone transposon.

SGI1-K, a Variant of the SGI1 Genomic Island Carrying a Mercury Resistance Region, in Salmonella enterica Serovar Kentucky

“…However, the estimated sizes of the products (3.5 kb, 2.0 kb, and 1.0 kb, respectively) were all about 0.7 kb smaller than predicted for the standard In4-type integron configuration (26), which is present at the right-hand end of In104 in SGI1 (Fig. 1) and SGI1-A to SGI1-J.…”

Characterization of a marine-isolated mercury-resistant Pseudomonas putida strain SP1 and its potential application in marine mercury reduction

“…P. putida SP1 possessed a mer operon as a mercury-resistant determinant like most of the other mercury-resistant bacteria, and the mer operon of P. putida SP1 was located on the chromosomal DNA as described in other strains (De et al 2003;Bafana et al 2010). Because multiple resistance genes are often located on mobile genetic elements (Mindlin et al 2001;Partridge et al 2001;Barkay et al 2003) and genes encoding for heavy metal resistance are often linked to antibiotic resistance genes on the same mobile element (Mindlin et al 2002;Barkay et al 2003), the similarity between the mer operon of P. putida SP1 and the mer operon located on Tn5041 suggested that the environmental bacterium P. putida SP1 may have acquired this chromosomal mer operon and other heavy metal or antibiotic resistance determinants through transposable elements that confer resistance to HgCl 2 and a variety of other xenobiotics.…”

Mercury Resistance in Bacterial Strains Isolated from Tailing Ponds in a Gold Mining Area Near El Callao (Bolívar State, Venezuela)

“…2C). Multiple resistance genes are most often located in mobile genetic elements [2,4,15], able to spread among the bacterial community very rapidly [6,12]. Considering that 62.96% of the Hgresistant bacterial strains harbored large, potentially conjugative plasmids, we were concerned by the potential acquisition of multiple resistances by human pathogens through conjugation with indigenous bacteria.…”