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Mural Pigment Biodeterioration by Streptomyces Through Metabolic Pathway
Akmal A. Sakr, Mohamed F. Ghaly, Howell Edwards and Yahia Elbashar

Streptomyces are involved in the chromatic alteration of mural paintings due to the metabolic production of acids, in particular oxalic acid which reacts with the blue azurite pigment (basic copper carbonate) to form the green color of copper oxalate and acetic acid which turns the green malachite pigment and blue azurite pigment colors into green verdigris (basic copper acetate). This can result in a misleading interpretation about the original pigments used historically in mural paintings .

Keywords: Streptomyces, copper oxalate, azurite, malachite green