Microcolonial fungi, long-living modified mycelia frequently occurring on desert and pseudodesert rock surfaces, are exposed to strong ultraviolet (UV) radiation, desiccation, and nutrient scarcity. They lack ascospores; all their cells grow by mitotic cell divisions and possess a thick melanized cell wall. Colonies of several randomly selected microcolonial strains were cultured and their structure was examined by cryo-scanning and transmission electron microscopy. Extracts of nine strains were analyzed by high performance liquid chromatography interfaced with mass spectrometry for the presence of mycosporines. These UV-absorbing compounds, common in spores and other survival structures, were thought to be limited to reproductive morphogenesis and unknown in growing hyphae. Mycosporines were present in eight of the strains, and mycosporineglutaminolglucoside (λmax = 310 nm; MH+ = 465) was the major mycosporine detected. Mycosporines present in the vegetative fungal microcolonies may be associated with the high survival potential, nonexpansive intracolonial growth, and longevity of these fungi. Intrahyphal growth and recolonization of old cells by new ones were observed in all strains investigated.Key words: mycosporines, microcolonial fungi, intrahyphal growth, survival, resting structures, rock surface.
Influences of the environment attack marble and ultimately destroy it. Especially the black yeast-like fungi which are often found on marbles especially in Mediterranean monuments strongly attack the marble. Colonization of the surface and interspaces inside the rock on experimental rock slabs lead to additional heat absorption and transfer. This imposes a higher dilatation of the marble causing losses of particles and ultimately the désintégration of the rock structure. For the first time the mechanical destruction of rock material by micro-organism is experimentally shown.
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