Bacterial and Geochemical Composition of Thrombolites from Lake Sarmiento, Torres del Paine National Park of Chilean Patagonia

Microbialites are organo-sedimentary structures formed as minerals precipitate due to the metabolic activity of microorganisms. They can be differentiated by their internal mesostructure into stromatolites and thrombolites. Lake Sarmiento, located in the Patagonia region of southern Chile, is a sub-saline alkaline lake in which living submerged and sub-fossil thrombolites are present. A submerged thrombolite was collected and one of the fragments was deposited in an experimental aquarium for 1.5 years, in order to examine possible changes to its biological and chemical composition. The bacterial biodiversity was examined using Illumina sequencing of PCR-amplified 16S V4 rRNA genes from total extracted DNA. The chemical structure was studied using XRD and bench chemical methods. The results show that in the living submerged and aquarium thrombolite samples, the Proteobacteria, Verrucomicrobia, Planctomycetes and Bacteroidetes phyla dominated the bacterial communities, which were similar at the upper taxonomic level. However, differences between the samples were detected at deeper classification levels (class, genus). Interestingly, no changes in the carbonate composition of the thrombolites were observed after culturing during 1.5 years. This study is the first to provide new insights into the bacterial community composition of thrombolites from this site. The thrombolites from Lake Sarmiento are active and contain a unique bacterial community composition. Further studies, including greater sampling and greater variety of experimental conditions in vitro (aquarium) will be helpful to create a global understanding of the microbial composition and formation of the thrombolites from Lake Sarmiento.