| Abstract: |
Patination and staining of rock surfaces is usually attributed to chemical redox processes and to soot deposition. A second type of patina (bio-patina) has been attributed to phototrophic microorganisms. It turns out, however, that chemoorganotrophic microbiota are widespread and often the most important inhabitants of rock surfaces. In this study the pigments of two natural rock samples with brightly orange patina, and the pigments produced by a coccoid bacterium and the fungus Gibberella intricans that have both been isolated from these rock samples, are analysed by ultraviolet-visible spectroscopy and mass spectrometry. This chemical analysis shows that the fungus and the bacterium produce carotenoids that are the same as those found on the natural rock samples. Thus, the direct relation between the patination of the rocks and the rock-inhabiting microbiota is demonstrated. Further, it is shown by cultivation of the fungus and the bacterium on freshly cut marble that both organisms can rapidly create coloured patinas under laboratory conditions. It is concluded that a major source of coloured patinas on rocks are microbially produced pigments such as carotenoids.
|
