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Torbjorg Bjelland, University of Bergen (Norway)
Martin Grube, Karl-Franzens-Universität Graz (Austria)
Frida Lise Daae, University of Bergen (Norway)
Ingunn H. Thorseth, University of Bergen (Norway)
Lise Ovreas, University of Bergen (Norway)
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Lichens cover an estimated 10 percent of the planet's surface. They are among the earliest species in primary succession of rock-surfaces and in general the most common and visual colonizers of rocks. Crust-forming epilithic lichens are attached with their entire surface to the supporting substrate and their hyphae can massively penetrate into the weathering rind of porous rocks. Lichens have an effect on the degradation of rocks, leading to fragmentation, textural and chemical changes of the rock and to its component minerals. Preliminary data suggest a diverse community of Bacteria, Archaea and Eukarya (e.g. algae and fungi) to inhabit the lichen-mineral interface, though biologically mediated weathering of rock is likely to be a more complex phenomenon than expected.
The microbial communities associated with the thallus of four crustose rock-inhabiting lichens (Ophioparma ventosa, Pertusaria corallina, Rhizocarpon geographicum, and Hydropunctaria maura) and the underlying rock substrates (arcosic metasandstone) were analysed by PCR-DGGE profiling and sequencing of representative bands. Profound differences were detected between the endolithic substrate and the epilithic lichen communities, and between communities in different species of lichens. This can partly be explained by differences in the ecological requirements of the lichens. Bacteria in the lichens belong to major lineages including Alpha-, Beta-, Gammaproteobacteria, Actinobacteria, and Cyanobacteria. All the Archaea affiliated with the Crenarchaeota. The intertidal lichen H. maura show a distinct microbial community which include the genuine Eukarya photobiont, a number of Archaea and many different lineages of Bacteria. Cyanobacteria and Deinococcus were only found associated with H. maura. These data provide evidence for unique microbial communities in different lichen species (both epi- and endolithic), which may depend on various micro-ecological factors of the host symbiosis, including secondary metabolites, morphological structure, and photosynthetic partner, as well as local variations in the geochemical and mineralogical composition of the sandstone. The microbial diversity appears to be higher in the underlying rock substrate (here called the hypothallosphere) than within the algal containing part of the lichen thalli.
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