Archaeal diversity: temporal variation in the arsenic-rich creek sediments of Carnoulès Mine, France.

The Carnoulès mine is an extreme environment located in the South of France. It is an unusual ecosystem due to its acidic pH (2-3), high concentration of heavy metals, iron, and sulfate, but mainly due to its very high concentration of arsenic (up to 10 g L⁻¹ in the tailing stock pore water, and 100-350 mg L⁻¹ in Reigous Creek, which collects the acid mine drainage). Here, we present a survey of the archaeal community in the sediment and its temporal variation using a culture-independent approach by cloning of 16S rRNA encoding genes. The taxonomic affiliation of Archaea showed a low degree of biodiversity with two different phyla: Euryarchaeota and Thaumarchaeota. The archaeal community varied in composition and richness throughout the sampling campaigns. Many sequences were phylogenetically related to the order Thermoplasmatales represented by aerobic or facultatively anaerobic, thermoacidophilic autotrophic or heterotrophic organisms like the organotrophic genus Thermogymnomonas. Some members of Thermoplasmatales can also derive energy from sulfur/iron oxidation or reduction. We also found microorganisms affiliated with methanogenic Archaea (Methanomassiliicoccus luminyensis), which are involved in the carbon cycle. Some sequences affiliated with ammonia oxidizers, involved in the first and rate-limiting step in nitrification, a key process in the nitrogen cycle were also observed, including Candidatus Nitrososphaera viennensis and Candidatus nitrosopumilus sp. These results suggest that Archaea may be important players in the Reigous sediments through their participation in the biochemical cycles of elements, including those of carbon and nitrogen.