Expression of copper-resistance genes in microbial communities under copper stress and oxic/anoxic conditions.

Microorganisms have developed copper-resistance mechanisms in order to survive in contaminated environments. The abundance and expression of the copper-resistance genes cusA and copA, encoding respectively for a Resistance Cell Nodulation protein and for a P-type ATP-ase pump, was assessed along a gradient of copper concentration in microcosms prepared from Seine estuary mudflat sediment. We demonstrated that the abundance of copA and cusA genes decreased with the increase of copper concentration and that cusA gene was up to ten times higher than the copA gene. Only the copA gene was expressed in both oxic and anoxic conditions. The abundance and activity of the microbial community remained constant whatever the concentrations of copper along the gradient. The molecular phylogeny of the two copper-resistance genes was studied and revealed that the increase of copper increased the diversity of copA and cusA gene sequences.