Crenarchaea And Bacteria From Subterranean Springs

Thermal springs, delivering their water from deep reservoirs, are in contact with the rock-dwelling subsurface biosphere and can transport members from these environments to the surface. They are thus a link between surface and subsurface. Although the environments may vary greatly in mineral composition, extent and depth, springs provide an access to explore the hidden biosphere, which would be difficult to achieve otherwise.

A culture independent molecular analysis of microbial communities on rocks and in the water of a moderately thermal spring (46°C) in the Central Alps near Bad Gastein, Austria, was performed. Four hundred fifteen clones were analyzed (Weidler et al., 2007); about 130 were found to be affiliated with 14 bacterial operational taxonomic units (OTUs) and about 280 with 4 archaeal OTUs. The majority of the cloned archaeal 16S rRNA gene sequences belonged to the so-called soil-freshwater-subsurface (1.1b) crenarchaeal group, according to DeLong (1998) and Jurgens et al. (2000); other representatives belonged to the freshwater-wastewater-soil (1.3b) group, except one clone, which was related to a group of uncultivated Euryarchaeota. These findings supported recent reports that Crenarchaeota do not only exist in high-temperature environments (DeLong, 1998; Bintrim et al., 1997; Schleper et al., 2005), but are probably wide-spread in rather temperate ecosystems. Most of the bacterial sequences were related to the Proteobacteria (a, f, y and S), Bacteroidetes and Planctomycetes. One OTU was allied with Nitrospina sp. (S-Proteobacteria) and three others grouped with Nitrospira. Since Crenarchaeota have been implicated recently in the nitrogen cycle (Treusch et al., 2005), the spring environment was also probed for the presence of one of the key enzymes, the ammonia monooxygenase subunit A (amoA) gene. Sequences were obtained which were related to crenarchaeal amoA genes from marine and soil habitats. The data suggested that nitrification processes are occurring in the subterranean environment and that ammonia could possibly be an energy source for the resident communities (Weidler et al., 2007).

Probing biofilms in the spring with fluorescently labeled oligonucleotides directed against portions of the 16S rRNA genes of bacteria revealed numerous morphologies, most notably single cells and chains of bacteria (Fig. 4, left panel); similar hybridisation experiments were performed with archaea-specific sequences and showed mainly short rods or coccoid cells (Fig. 4, right panel) of uncultured archaea; similar archaeal morphologies were reported recently from a Siberian spring by Hatzenpichler et al. (2008), who discussed in their paper also the early evolution of nitrogen cycling.

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