Biodecay of cultural heritage as a space/time-related ecological situation — an evaluation of a series of studies

Abstract

Mural paintings and stone monuments are exposed to natural and man-made hazards for time spans sometimes longer than 10,000 years without total decay. On the other hand, a high percentage of the mineral physical heritage suffers severe damage and even total loss within a few decades. Several factors influence this general situation. The mural paintings of Lascaux and Altamira had been stabilized in a protective environment for millennia until they were re-exposed to severe environmental risks. Wall paintings and stone sculptures may remain unaltered for many years through: (1) stabilized and protective environments, (2) development of a protective patina (biofilm, minerals, organics) or, (3) more recent additional paint or mortar layers, which themselves are exposed to environmental hazard instead of the fresco underneath. Natural or artificial coverage, however, will invariably hinder evaluation and appreciation of the object of art. Detrimental microorganisms often only sporadically interact with these precious paintings. Many microbes settling on and in mural paintings are of a unusual metabolic type, namely poikilotrophic organisms. These poikilotrophs are capable of forming a biocoenosis on and in mural paintings, which may establish itself within a few months or years and then remains unchanged in a dormant or non-cultivable state for many years, or even centuries. The same holds true for chemical and physical alterations brought about by microorganisms. After a damaging initiation period of growth, the microflora may turn into a biofilm, which continues to live at extremely low levels of metabolic activity. In this way, detrimental chemical, physical and biological activities may be screened or shielded off for a very long period of time. In order to understand these processes, we have studied poikilotroph sub-aerial biofilms of mural paintings and sculptures excavated after long periods of dormancy. Several methods for the characterization of the physical properties of the colonies of fungi involved in colonization and deterioration of mural paintings and stone monuments are described. The fairy-tale of “The Sleeping Beauty” maybe an excellent metaphor for this phenomenon. The main issue, however, is to understand the physical or mechanical impact of the poikilotroph flora on the materials of the physical heritage studied.