The bioremoval of nitrate and sulfate alterations on artistic stonework: The case-study of Matera Cathedral after six years from the treatment

Abstract

The bioremoval of nitrate and sulfate salts from the tuff stone surfaces of 12th century Matera Cathedral, which had been altered by nitrates and sulfates, using nitrate and sulphate reducing bacteria was performed. The bioremoval treatment was based on the direct application onto the altered stone surfaces of a previously-isolated Pseudomonas pseudoalcaligenes KF707 strain and Desulfovibrio vulgaris ATCC 29579 cells. The two strains were entrapped in a Carbogel and applied individually and together to the vertical wall; the protocol adopted included a multilayer biosystem, as a solution to maximise the efficacy of the biocleaning process on artistic stonework. The biological procedure resulted in the efficient, homogeneous removal of surface deposits and salt alterations. In fact, at 24 h the strains had removed 55% of the nitrate and 85% of the sulfate deposits, respectively. After six years from the original application the results show further improvements in microbial technology when applied to “bioremoval” and “biocleaning” of cultural heritage surface alterations.