Hydrolyzes the N-acetamido groups of N-acetyl-D-glucosamine residues in chitin to form chitosan and acetate (By similarity). Chitosan is required to anchor melanin to the cell wall, for maintenance of cell wall integrity, and for proper cytokinesis (By similarity). Chitosan offers an advantage during infection as it is less readily detected than chitin by host immunosurveillance mechanisms (By similarity). [(1->4)-N-acetyl-beta-D-glucosaminyl](n) + n H2O = n acetate + chitosan Belongs to the polysaccharide deacetylase family.