Catalyzes the N-deacetylation of poly-beta-1,6-N-acetyl-D-glucosamine (PNAG, also referred to as PIA), a biofilm adhesin polysaccharide. N-deacetylation is crucial for attachment of the polysaccharide to the bacterial cell surface; it leads to the introduction of positive charges in the otherwise neutral PIA polymer, allowing electrostatic interactions (By similarity). Attached to the cell surface. Belongs to the polysaccharide deacetylase family.