Picocyanobacterial assemblages in ultraoligotrophic Andean lakes reveal high regional microdiversity

Picocyanobacteria (Pcy) diversity was studied in a set of ultraoligotrophic North Patagonian Andean lakes. The glacial lake system includes a central lake (Lake Nahuel Huapi, with its side basin, Lake Moreno) and four satellite lakes (Lakes Espejo, Correntoso, Gutierrez and Mascardi) derived from a larger paleolake. Automated ribosomal intergenic spacer analysis showed a Pcy community structure composed of 18 operational taxonomic units (OTUs), of which only one (OTU 1094) was widely distributed, being found at all depths in all of the lakes. Most of the others were observed in a few of the lakes. The principal component analysis revealed the habitat specificity of some Pcy OTUs: the satellite lakes have a highly irradiated epilimnion, while the central lake has a well-mixed euphotic zone that does not extend beyond the epilimnion. We also observed a distinctive vertical distribution of the OTUs and a significant correlation between Pcy chlorophyll-specific primary production and OTU 738, which was only found in the satellite lakes. Lastly, the high beta-diversity of this lake district supports the hypothesis that microdiversity is higher in glacier-derived lake systems where habitat fragmentation due to geographic barriers results in rapid speciation.