Anthropic effect on the lichen colonization in building stones from cultural heritage

In this study the effect of human urine on lithobiontic microorganisms colonizing stone materials from the cultural heritage was evaluated in situ by means of a field experiment in a historic quarry (Redueña dolostone quarry, Madrid, Spain). With this experiment, it was possible to assess the effect of this bioproduct when interacting with the existing lithobiontic microbial community at the most real conditions. The application of the bioproduct was performed by directly spraying onto the rock surface of the quarry front with abundant lichen colonization during 8 weeks (one application per week). After the application, the structure of Verrucaria nigrescens lichen thalli and the ultrastructure of their algal and fungal cells components resulted to be affected. The upper cortex of the lichen thalli was particularly affected, with damage-like fungal cells, and even in some cases, disappeared, leaving unprotected and exposed algal cells to environmental conditions.