, 2012). It GSK3235025 has been reported that V(IV) binds to the surface of certain proteins (Nishida et al., 2009); however, it is not known whether this property

is shared by the V(III) used in this study. Since exposure to Zn, Cu and Cd resulted in a decrease in the conjugation rate, the increased conjugation rate observed following V exposure might have been the result of specific physiological effects similar to those associated with Ca (Takeo, 1972). Chemical interactions between biomolecules and V should be studied to determine the mechanism by which V facilitates the acquisition of OTC resistance through HGT. To determine whether the observed increased rate of OTC resistance also occurs in the natural environment, we determined the V concentration and rate of OTC resistance in samples of marine sediment. As shown in Fig. 2, the proportion of OTC-resistant bacteria increased with an increase in the concentration of V. Although regression analysis revealed a significant positive correlation between the proportion of OTC-resistant bacteria and V concentration on medium containing 120 μg mL−1 of OTC (P = 0.023), this correlation was not significant on medium containing 60 μg mL−1 of

Trametinib concentration OTC (P > 0.1). Similarly, no positive correlation was observed between the sediment concentrations of Zn, Cu or Cd and OTC resistance, even though exposure to these metals suppressed acquisition of OTC resistance in E. coli JM109

(data not shown). The positive correlation between V concentration and OTC resistance suggests that more copies of OTC resistance genes may be present in sediments containing higher V concentrations. The rate of HGT increased at V concentrations of 500–1000 μM (1000 μM is equivalent to 157 μg mL−1). The maximum concentration of V in marine sediment was 140 μg g−1 of dry sediment (Fig. 2), which is within the range of HGT elevating concentrations. Despite the fact that our sediment sample was collected Methocarbamol in the open ocean, where ship traffic level is not high, the concentration of V was at a level sufficient to stimulate HGT, thus confirming that the V does appear to accumulate in open ocean sediment. Tamminen et al. (2011) reported that tet genes are highly persistent and do not disappear from aquaculture sites, even after several years without antibiotic use. The presence of residual V in coastal marine sediments is thus of concern as this may lead to the preservation and/or spread of antibiotic resistance genes in the marine environment. The susceptibility of bacteria to V-containing compounds varies (Fukuda & Yamase, 1997; Aendekerk et al., 2002; Denayer et al., 2006).