Plasmids pMOL28 and pMOL30 of Cupriavidus metallidurans are specialised in the maximal viable response to heavy metals

We fully reannotated two large plasmids, pMOL28 (164 ORFs; 171 459 bp) and pMOL30 (247 ORFs; 233 720 bp), in the genome of Cupriavidus metallidurans CH34. Genes involved in the resistance to the heavy metals Co(II), Cr(VI), Hg(II), and Ni(II) are concentrated within a region of 34kb on pMOL28; those involved in the resistance to Ag(I), Cd(II), Co(II), Cu(II), Hg(II), Pb(II), and Zn(II) occur within a 132kb region on pMOL30. We identified putative genomic islands containing metal-resistance operons flanked by mobile genetic elements, one on pMOL28 and two on pMOL30. Transcriptomic analysis using quantitative PCR and microarrays revealed the metal-mediated up-regulation of 83 genes on pMOL28 and of 143 genes on pMOL30 that coded for all known heavy-metal resistance proteins, membrane proteins, truncated transposases, conjugative transfer-proteins, and many unknown proteins, and for some new ones (czcJ, mmrQ, and pbrU). Five genes on each plasmid were down-regulated; for one of them, chrI localised on pMOL28, this occurs in the presence of five cations. We observed multiple cross-responses ,suggesting that the cellular defences of C. metallidurans against heavy metal stress involves various regulons, and probably has multiple stages including a more general response, and a more metal-specific one