Partitioning of Thaumarchaeota populations along environmental gradients in high mountain lakes.

We investigated the spatial distribution and diversity of ammonia-oxidizing Archaea (AOA) across gradients of pH, trophic status and altitude in a set of high mountain lakes (Limnological Observatory of the Pyrenees, north-east Spain). Both phylogeny- and taxonomy-based approaches revealed well-defined AOA community patterns with pH as the main potential driving environmental factor. The I.1a and SAGMGC-1 Thaumarchaeota clusters, and their potentially associated amoA gene variants (clusters Fresh 5 and Soil/Fresh 1, respectively) showed highest relative abundances in the most oligotrophic lakes. Euryarchaeota (i.e. HV-Fresh cluster, Methanomicrobiales and Thermoplasmatales) dominated in lakes with higher trophic status. Phylogenetic diversity (PD) in Pyrenean lakes was 1.5- to 2.3-fold higher than the PD from an equivalent number of globally distributed marine and soil sites. We observed segregated distributions for SAGMGC-1, preferentially distributed in the lakes with the lowest pH (< 5) and the highest nitrite concentration (> 0.12 μm), and I.1a in lakes with lower nitrite and dissolved organic carbon concentrations below 0.5 mg L(-1) . Overall, these results showed strong selection by local environmental conditions, unveiled new ecological niches for freshwater SAGMGC-1 in low pH oligotrophic lakes, and suggested specific and successful adaptations of planktonic archaea to the high mountain lakes landscape.