New Undescribed Lineages of Non-extremophilic Archaea Form a Homogeneous and Dominant Element Within Alpine Moonmilk Microbiomes

The moonmilk deposits within the alpine Hundsalm cave in Austria offered the opportunity to investigate anthropogenically uninfluenced microbiomes. Via cultivation experiments we were able to show that the communities were cold-adapted and oligotrophic. Combined qPCR, DGGE, cloning and sequencing data further highlighted that the archaeal community basically comprises a low number of species, though highly abundant. These organisms are assumed to form new lineages within the <i>Euryarchaeota</i>, while the detected <i>Thaumarchaeota</i>, closely related to ammonium oxidizers, form a second, but minor, abundant group within the moonmilk deposits. Moreover, in terms of abundance the archaeal community clearly outnumbers bacteria (e.g., genera <i>Pseudomonas, Flavobacterium</i> and <i>Rhodococcus</i>) and fungi within the investigated microbiomes. In contrast to the highly complex bacterial and fungal communities, only a low number of archaeal species form a constant and essential element within the moonmilk speleothems and other cave-internal habitats.