Microbiological analysis of mortars from the church of San Juan del Mercado at Benavente, Spain

Two relatively recent techniques, epifluorescence microscopy and flow cytometry have been applied to the study of microorganisms in the mortars and frescoes of the church of San Juan del Mercado, Benavente, Spain. These results have been compared to those obtained with conventional techniques, the former showing clear advantages over the latter. Thus, with the aim of obtaining data, not only on the nature of the mortars themselves, but also on the metabolic products of the microorganisms, SEM-EDX and FT-IR analyses have also been carried out and considerable amounts of sulphates and nitrates have been detected. These results, taken together with the high microorganism count lead to the conclusion that the microorganisms possess high metabolic activities which necessarily influence the physico-chemical properties of the mortars.