References

Role of Microorganisms in Wear Down of Rocks and Minerals 67
Fig. 2. SEM-micrograph of etching and mechanical decohesion activity by a complex microbial
community on marble from a quarry in Carrara (Italy). The multi-compound subaerial
biofilm is composed of heterotroph free-living fungi (filamentous and yeast-like), microscopic
unicellular algae and accompanying bacteria. Macroscopically, the marble surface
has a slightly gray surface appearance created by numerous tiny microcolonies disguising
the original shiny white of the marble. The biological growth and wear down partially follow
the cleavage zones between the marble grains. However, some hyphae and yeast-like cells
of the fungi penetrate through the crystals without following any weakness of the mineral
structure (see Fig. 3), thus drastically increasing the contact surface between the biofilm
and the rock material
Warscheid et al. 1991). Even in remote places such as the world’s large
deserts, heterotrophic fungi settle on rocks without any support from autotrophic
algae or symbiotic algal partners within lichens (Staley et al.
1982; Gorbushina and Krumbein 1999, 2000). As a matter of fact, freeliving
fungi are the most enduring organisms under extremely changeable
desert conditions with rainfall below 180 mm/year (Perry 1979). They are
widely abundant cosmopolite invaders of air-exposed rock surfaces and
prevailinallsoilformationprocessesaswell.