Moreover, none of these resistance genes was detected to lay within the HSs under our buy GSK1120212 analysis conditions, such as the dfrA1 cassette in HS3 in four previously reported ICEs [23, 39]. However, we cannot rule out the possibility of resistance determinants present elsewhere in the ICEs or in host genomes independently of ICE sequences. The former hypothesis seems

more likely, for the successful transmissibility of the antibiotic resistance (Sulr and Stpr) between two Vibrio strains V. cholerae Chn108 and V. parahaemolyticus Chn25 and E. coli MG1655 has been demonstrated BVD-523 manufacturer by conjugation experiments (see below). The rumB and rumA genes encode a UV repair DNA polymerase and a UV repair protein, respectively [41]. Environmental strains tend to conserve ICEs devoid of antibiotic resistance genes by keeping a functional rumBA, compared with clinical strains not exposed to UV but to antibiotics [9]. Moreover, most of the ICE antibiotic resistance genes are found within transposon-like

structures [23]. These may serve as a good explanation as to why typical antibiotic resistance gene clusters were not detected in the VRIII of the ICEs characterized in this study. Exclusion system Entry exclusion systems specifically inhibit redundant conjugative transfers between cells that carry identical or similar elements [42, 43]. SXT and R391 carry genes for an entry exclusion XAV-939 in vitro system mediated by two inner membrane proteins, TraG and Eex, which are expressed in the donor and recipient cells, respectively

[44]. Consistent with previous results [10, 43], the ICEs characterized in this study fell into two exclusion groups, S and R (Figure 2). Multiple sequence alignments revealed that the S group elements encode EexS proteins with typical exclusion sequences [45] in their carboxyl termini as known EexS proteins in public databases (data not shown). They also encoded TraGS proteins with exclusion determinant residues P-G-E [43]. In contrast, four elements including ICEVchChn2, ICEVpaChn1, ICEVpaChn3 and ICEValChn1 fell into the R group, which encode the EexR, and TraGR proteins with characteristic exclusion filipin T-G-D residues (data not shown). It was reported that R391 and pMERPH, belonging to the R exclusion group, contain a DNA insertion conferring resistance to mercury immediately downstream of their respective eexR and eexR4 genes [29, 45]. Unexpectedly, in our study, neither the R nor the S group strains that display strong mercury resistance phenotypes was detected to carry any inserted sequence between the eeX and traG genes under our analysis conditions. The results suggest that the mercury resistance determinants or heavy metal efflux pumps mediating the resistance phenotypes may be present in additional loci in the ICEs, or in their host genomes independently of the ICE sequences. The latter hypothesis seems more likely based on the conjugation experiments.