Ecosystem Mural
In addition to moisture and air pollution, microorganisms play a significant role in the decay of old murals. Since the harmful effects of microbes were recognized a few years ago, strategies to protect art objects from microbial destruction have been sought worldwide. Scientists from the Institute for Microbiology and Genetics at the University of Vienna have now applied and further developed a time-saving method of identifying microorganisms. In principle, every surface is a potential settlement area for countless microorganisms. Even valuable wall paintings are not immune to colonization with bacteria, fungi and algae. They lose the paint layer and show discolouration. The list of microbes found on murals is so long that Sabine Rölleke from the Institute of Microbiology at the University of Vienna speaks naturally of the "ecosystem mural" given the large number of microbial populations.
In order to determine which microorganisms are involved, the microbes found in the painting samples often had to be cultivated in the laboratory for months and examined for their physiological characteristics. However, only a small percentage of the organisms could be cultivated at all, so that one had to fear that only a small part of the spectrum of species would be recorded at all.
The method developed by the Vienna research team is based on the differentiation of the genetic code of the respective microbe species. With it, the smallest painting samples – a sample area the size of a ballpoint pen tip is sufficient – can be used to examine a much larger section of the organisms actually present in a short time.
The starting point for the molecular-biological method, according to Sabine Rölleke, is the polymerase chain reaction (PCR). With their help, specific ribosomal DNA sequences in the sample can be rapidly amplified under the influence of heat, so that visible quantities of identical DNA sequences are produced. In a further step, the cocktail of different DNA sequences is arranged into band patterns using denaturing gradient gel electrophoresis (DGGE), in which each band then represents a bacterial species in the starting material. The more bands are contained per sample, the greater the variety of bacteria.
To identify the species, the bands can be cut out of the gel and their DNA sequence compared with those of previously known bacteria from DNA databases. With regular monitoring using this method, the success of conservation measures can be checked without a great deal of time, shifts in the population can be recognized and further steps can be taken.
