Microbial metacommunities in the lichen–rock habitat Torbjørg Bjelland, 1,2 * Martin Grube, 3 Solveig Hoem, 1,2 Steffen L. Jorgensen, 1,2 Frida Lise Daae, 1,2 Ingunn H. Thorseth 2,4 and Lise Øvreås 1,2 1 Department of Biology, 2 Centre for Geobiology and 4 Department of Earth Science, University of Bergen, Postboks 7803, N-5020 Bergen, Norway. 3 Institute of Plant Sciences, Karl-Franzens-Universität Graz, Holteigasse 6, A-8010 Graz, Austria. Summary Lichens are common as colonizers of bare rocks and contribute to weathering, but their associated bacte- rial communities have been poorly studied. In this study Hydropunctaria maura, Ophioparma ventosa, Pertusaria corallina and Rhizocarpon geographicum were analysed to determine the influence of lichens on lichen–rock-associated microbial metacommunities. For the first time, Archaea were documented to be associated with rock-inhabiting lichens. All the archaeal sequences obtained were affiliated with Cre- narchaeota. The Bacteria detected in the lichen–rock samples were affiliated with the major lineages Acido- bacteria, Actinobacteria, Alpha-, Beta-, Gammaproteo- bacteria, Bacteriodetes, Chloroflexi, Deinococcus, Firmicutes, Planctomycetes, Tenericutes and Cyano- bacteria. The microbial communities of O. ventosa, P. corallina and R. geographicum were more similar to each other both terms of the number and types of different sequences, than to H. maura. A higher bacte- rial diversity was observed endolithically than within the epilithic lichen thalli directly above. The abun- dance of Archaea were also generally higher endolithi- cally than in the epilithic lichen thalli, while the abundance of Bacteria was higher in the lichen thalli compared with within the rock. These results demon- strated that the lichen–rock interfaces are complex habitats, where the macroscopic lichens influence the composition of microbial metacommunities. Introduction With their attractive colours and distinct morphologies, lichens are the first conspicuous colonizer of exposed rock surfaces. Lichens have been estimated to cover as much as 6% of the planet’s terrestrial surface (Haas and Purvis, 2006), and they are important agents in early stage rock weathering and soil formation (Gadd, 2007). Their vegetative bodies, or thalli, can be regarded as miniature ecosystems, which by definition consist of at least two organisms, a fungus and its eukaryotic and/or prokaryotic photosynthetic partner. Lichens allow the fungal and algal partners to thrive under ecological conditions that would not support the partners in non- symbiotic stages. The symbiotic relationship enables the partners to apparently tolerate a wide range of external stress factors including extreme fluctuations of tempera- tures, desiccation and salinity. Lichens, and in particular crust-forming rock inhabitants, grow at extremely slow rates, and undisturbed individuals can reach ages of several thousand years (Denton and Karlén, 1973). As such they act as generators of ecological niches for other indigenous rock-inhabiting microbial communities, either within the thalli or in the weathered rock below. Crust-forming epilithic lichens (a morphological group of lichens) are attached with their entire surface to the sup- porting substrate, and their hyphae can penetrate mas- sively and relative deeply into the weathering rind of rocks. The thickness of the hyphal layer formed by the lichen fungus inside the rock can be ~10 times as thick as the symbiotic thallus, which is visible at the surface of the rock (Bjelland and Ekman, 2005). The endolithic part rep- resents a significant component of the entire ecosystem of a crustose rock-inhabiting lichen. Lithic substrate is considered to be an important part of the biosphere; however, it remains poorly explored. Epi- and endolithic microbial communities are believed to play an important role in degradation and weathering of rocks, and in the global cycling of elements and nutrients (Kon- hauser, 2007). Microorganisms colonize exposed rock surfaces, or the rock fabric adjacent to the surface, in a wide variety of climates and environments (Konhauser, 2007). Representatives from all three domains of life, Bacteria, Archaea and Eukarya (e.g. algae and fungi), are common endolithic colonizers (e.g. Walker and Pace, 2007). Studies of subsurface microbial communities indi- cate that rocks harbour distinctive microbial communities (Lysnes et al., 2004; Bjelland and Ekman, 2005; Herrera et al., 2008; Santelli et al., 2008; Mason et al., 2009). Lichen–mineral interfaces (see Piervittori et al., 2004 for lists of references) represent the best-studied terrestrial endolithic communities. However, these works have Received 8 March, 2010; accepted 30 June, 2010. *For correspon- dence. E-mail torbjorg.bjelland@bio.uib.no; Tel. (+47) 55 58 35 73; Fax (+47) 55 58 37 07. Environmental Microbiology Reports (2011) 3(4), 434–442 doi:10.1111/j.1758-2229.2010.00206.x © 2010 Society for Applied Microbiology and Blackwell Publishing Ltd