Читать книгу Monument Future - Siegfried Siegesmund - Страница 124

Our historic built heritage consists mainly out of natural building stones. As these stones interact with the environment, their properties slowly alter and the stones degrade. On limestones, gypsum crusts are among the most abundant deterioration features. These are sulphate encrustations that incorporate airborne dust, giving them a black appearance (Camuffo, Del Monte and Sabbioni, 1983). There is a strong correlation with pollution, especially with SO₂ and NO_x. It has been regarded that atmospheric SO₂ oxidizes and forms H₂SO₄, 96which will transform CaCO₃ to gypsum. NO_x acts as a catalyst (Bai, Thompson and Martinez-Ramirez, 2006).

Besides air pollution, biodeterioration by lichens, algae, fungi, archaea and bacteria can alter building stones significantly. Several groups of prokaryotes produce acids, chelating agents and pigments leading to dissolution and discolouration. (Doehne and Price, 2010). Some autotrophic prokaryotes can oxidize sulphur or nitrogen compounds and produce respectively H₂SO₄ or HNO₃. By other means they can turn air pollutants such as NO_x and SO₂ into nitrates and sulphates and can play a role in gypsum crust formation (Doehne and Price, 2010). Those prokaryotes have been isolated and sequenced from buildings and a correlation between air pollution and their occurrence has been indicated (Mansch and Bock, 1998; Villa et al., 2015; Li et al., 2016) Laboratory tests by Mansch and Bock (1996) show an increase of gypsum formation in the presence of nitrifying bacteria. The role of nitrogen and sulphur oxidizers in gypsum crust formation is still unclear and for this reason we sampled specifically gypsum crusts of Lede stone at the city and the countryside (De Kock et al., 2015), to characterize the prokaryotic community and to test if they can alter natural building stones.

This manuscript will focus on sulphur and nitrogen oxidizing prokaryotes and the discolouration potential of one of the isolates. A more in-depth description of the whole microbial community can be found (Schröer et al., 2020).