Reduces the permeability of the outer membrane to copper. Seems to be involved in the regulation of biofilm formation. May decrease biofilm formation by repressing cell-cell interaction and cell surface interaction. Repressed by ComR. Induced by copper via release of ComR. Induced in biofilms and by several stress conditions. Disruption of this gene increases copper sensitivity, induces stress response genes in biofilms, increases aggregation and cell surface hydrophobicity, and decreases indole synthesis. Belongs to the BhsA/McbA family.