Picocyanobacterial assemblages in ultraoligotrophic Andean lakes reveal high regional microdiversity

Abstract

Picocyanobacteria (Pcy) diversity was studied in a set of ultraoligotrophic NorthPatagonian Andean lakes. The glacial lake system includes a central lake (LakeNahuel Huapi, with its side basin, Lake Moreno) and four satellite lakes (LakesEspejo, Correntoso, Gutie´rrez and Mascardi) derived from a larger paleolake.Automated ribosomal intergenic spacer analysis showed a Pcy community structurecomposed 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 componentanalysis revealed the habitat specificity of some Pcy OTUs: the satellite lakes havea highly irradiated epilimnion, while the central lake has a well-mixed euphoticzone that does not extend beyond the epilimnion. We also observed a distinctivevertical distribution of the OTUs and a significant correlation between Pcy chlorophyll-specific primary production and OTU 738, which was only found in the satellitelakes. Lastly, the high ß-diversity of this lake district supports the hypothesisthat microdiversity is higher in glacier-derived lake systems where habitat fragmentationdue to geographic barriers results in rapid speciation.