Author:

Susana del Carmen De la Rosa-García, Otto Ortega-Morales, Christine Claire Gaylarde, Miguel Beltrán-García, Patricia Quintana-Owen, Manuela Reyes-Estebanez

Date: 16 July 2012

Abstract:

Abstract. Deteriorated limestone from Mayan buildings in Yucatan, Mexico, was analyzed with scanning electron microscopy (SEM) and microprobe with energy dispersive X-ray analysis (EDAX), X-ray diffraction (XRD) and Fourier-Transformed Infrared Spectroscopy (FTIR). Changes in surface chemical composition, caused by the biofilm layer and the conversion of calcite into gypsum, were demonstrated. Representative fungi include Aspergillus, Penicillium, Fusarium and Paecilomyces. Strains of Aspergillus niger and Penicillium sp., were selected for their ability to produce acidic metabolites. Both fungi excreted organic acids when incubated; ion exchange chromatography identified these acids as gluconic, succcinic-malic (coeluted) and oxalic. A. niger, the most active acid producer, also excreted citric acid. when grown in the presence of limestone coupons, calcium release from the mineral matrix paralleled the production of oxalic acid. However free calcium was considerably lower in filtrates from limestone coupon-containing culture, suggesting its complexation. SEM and EDAX confirmed that calcium oxalate crystals developed on the surface of the stone coupons. The results show that organic-acid-producing fungi may contribute to the deterioration of limestone monuments.Kew words: acidelysis, Aspergillus, biofilm layers, lime stone, Penicillium.

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