Carbonatogenic bacteria on the ‘Motya Charioteer’ sculpture

Abstract

The ‘Motya Charioteer’ marble statue, a masterpiece of ancient Greek sculpting, was discovered in 1979 on the island of Motya, Sicily. A general assessment of the statue's conditions in 2008 revealed that the marble has lost its luster and started to show some microcracks. In 2019 and in 2020, microbiological surveys were conducted to assess the marble's biodeterioration through the identification of bacteria capable of metabolizing calcium carbonate and damaging the statue. Bacterial strains with calcium carbonate dissolution properties were isolated exclusively from the damaged areas of the statue; among 31 strains showing calcium carbonate metabolism (precipitation and/or dissolution), 23 were bacilli. While causation cannot be confirmed, these bacterial strains are certainly capable of dissolving marble leading to statue degradation. In two damaged areas of the statue, Staphylococcus haemolyticus, a common component of human skin flora was identified. This strain demonstrated a fast calcium carbonate dissolution property, which has not previously reported for this species. Finally, two strains (Lysinibacillus fusiformis and Metabacillus litoralis), showed carbonatogenic features perfectly suitable for a bioconsolidation intervention on the sculpture.