Roles Played by MerE and MerT in the Transport of Inorganic and Organic Mercury Compounds in Gram-negative Bacteria

Abstract

In order to clarify the physiological roles played by MerP, MerT and MerE in Gram-negative bacteria, we constructed the plasmids pTP4 and pTPE21, which contained the genes merR, merT and merP, from the Pseudomonas K-62 plasmid pMR26, or the same genes with the merE gene of Tn21 from the Shigella flexneri plasmid NR1 (R100), respectively. Cells containing pTP4 showed increased hypersensitivity to Hg(II), but maintained a normal sensitivity to CH₃Hg(I). However, cells with pTPE21 exhibited increased hypersensitivity to Hg(II) and CH₃Hg(I). Cells with pTP4 accumulated appreciably more Hg(II) than control cells, but no significant difference was observed in their uptake of ¹⁴CH₃Hg(I). In contrast, the cells containing pTPE21 accumulated significantly larger amounts of Hg(II) and ¹⁴CH₃Hg(I) than either control cells or cells with pTP4. These results suggest that the mer operons have evolved to redirect uptake of mercurials into dedicated, specific and relatively high-affinity transport systems comprising the small periplasmic protein MerP and two inner membrane proteins, MerT and MerE.