Biodiversity analysis of the unique geothermal microbial ecosystem of the Blue Lagoon (Iceland) using next-generation sequencing (NGS)

The Blue Lagoon is a shallow geothermal lake which contains sea- and freshwater and is extremely high in silica content. This study has provided the first in-depth molecular survey of its planktic microbial inhabitants and laid the groundwork for future environmental and physiological work. Most MiSeq sequences obtained were affiliated with Alphaproteobacteria (36%), Cyanobacteria (26%), and Gammaproteobacteria (24%). Cyanobacteria were found to be the principal primary producers with 99.8% of the cyanobacterial sequences belonging to the unicellular Cyanobacterium aponinum. Filamentous genera: Halomicronema and Phormidium were very minor and present only outside the bathing area. The calculated diversity was typical of samples from extreme environments. Elevated salinity and high concentration of silicium attract extremophiles that are either highly adapted specialists for certain conditions or generalists with wide tolerance ranges. Relatively few abundant phyla were represented; 95% of observed OTUs consisted of less than ten sequences and only 0.5% had more than 1000 sequences. All rarefaction curves were far from saturation and a higher number of sequences is apparently required to cover the whole community diversity. Although, the diversity of the abundant taxa was limited, the rare biosphere, detectable only with next generation sequencing, increased significantly the diversity.