The Dry Valleys of South Victoria Land (Antarctica) are ice-free due to strong katabatic winds falling from the polar ice plateau. An average annual temperature of -22 °C, winter temperatures as low as -60 °C and a relative humidity of 14 to 47 % (Friedmann et al., 1987) provide an environment which was thought to be hostile to any life form (Horowitz et al., 1972). But Friedmann & Ocampo (1976) reported "cryptoendolithic" microorganisms in the pore space of weathering Beacon sandstone. This stratified microbial ecosystem usually consisted of an uppermost black zone of lichen fungi associated with green algae (Trebouxia), followed by a whitish layer containing fungi and bacteria, a green zone with algae (Hemichloris, Stichococcus) and cyanobacteria (Chroococcidiopsis sp.) and often a brown zone rich in iron oxides. The microbial composition and community structure varied depending on sandstone location and exposure. A considerable amount of work on these cryptoendolithic communities was published (Nienow & Friedmann, 1993), especially on those from Linnaeus Terrace (1600m, Asgard Range) and Battleship Promontory (Mt. Gran, Covoy Range). But sandstones of University Valley, New Moutain and Mt. Fleming (all close to the ice plateau) also had cryptoendolithic communities in favourably exposed locations (Hirsch, unpublished).
Microscopy of our samples and enrichments revealed ca. 170 different morphotypes (MT), with up to 66 MT per rock sample and none of the samples completely sterile. The total numbers in Linnaeus Terrace samples ranged from 2 MT (a white, newly colonized spot) to 24 (a horizontal rock slab), those from Battleship Promontory from 8 (an especially hard sample) to 66 MT (a gray and wet boulder). The number of prokaryotic MT exceeded in most cases that of eukaryotes. Several samples lacked phototrophs but had up to 13 different heterotrophic MT. Enrichments resulted in the isolation of >700 strains; several of these were new genera: Friedmanniella antarctica (Schumann et al.,1997), Hymeno-bacter roseosalivarius (Hirsch et al., 1998) and Modestobacter multiseptatus (Mevs et al., 2000). Other isolates represented new species of Deinococcus, Micromonospora, Blastobacter, Amycolata, Micro-coccus, Brevibacterium, Arthrobacter, Bacillus and Mycobacterium spp.
Of special interest were possible interactions among components of the endolithic communities. Analysis of organic compounds extracted from the community´s layers showed that carbohydrates, sugars, amino acids and organic acids were released and could thus be utilized by other organisms. Pure cultures studies with 66 bacteria and algae isolated from 2 adjacent samples of a boulder revealed many possible interdependencies among these organisms, especially with vitamins and organic acids, and growth experiments demonstrated that bacteria were stimulated by the presence of algal cultures (Siebert et al., 1996). Several strains released specific restriction endonucleases and utilized free DNA as sole source of C, N and energy. Resistance against extremely high Cr concentrations in this boulder was present in 1/3 of all bacteria and was plasmid-encoded. Isolation and characterization of such a plasmid showed that a plasmid transfer to Cr sensitive isolates by natural transformation occurred (Gliesche et al., 1996). Although competition for nutrients can be expected to occur within these communities, antibiotic interactions could not be observed. Thus it was shown that this extreme cryptoendolithic environment can be colonized by diverse communities of positively interacting microorganisms.
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