Metagenomic analysis of microbial mats from Brava and Tebenquiche lakes

Abstract

In this work, nucleic acid-based molecular methods, geochemical measurements andphysico-chemical characteristics were combined to investigate microbial sedimentary ecosystems ofLaguna Tebenquiche and Laguna Brava. Molecular diversity of two hypersaline microbial mats wascompared by WGS sequencing of environmental DNA from the mats.Brava and Tebenquiche are lakes in the Salar de Atacama, Chile, where microbial communities aregrowing in extreme conditions, including high salinity, high solar insolation, and high levels of metalssuch as lithium, arsenic, magnesium, and calcium. Evaporation creates hypersaline conditions inthese lakes and mineral precipitation is a characteristic geomicrobiological feature of these benthicecosystems. Microsensor measurements on the mats allowed determination of depth profiles of O2and sulfide, showing active production and respiration.The mat from Brava was more rich and diverse, with a higher number of different taxa and withspecies more evenly distributed. At the phylum level, Proteobacteria, Cyanobacteria, Chloroflexi,Bacteroidetes and Firmicutes were the most abundant, including ~75% of total sequences. At thegenus level, the most abundant sequences were affilitated to anoxygenic phototropic bacteria from thegenera Roseoflexus, Chloroflexus and Oscillochloris, followed by cyanobacterial genera such asMicrocoleus, Cyanothece and Nostoc. In Tebenquiche mats, Proteobacteria and Bacteroidetescovered ~70% of the sequences, with Cyanobacteria and Firmicutes including 5% each. Over 13% ofthe sequences were affiliated to Salinibacter genus, thus addressing the lower diversity. OtherBacteroidetes genera with more than 1% abundance included Rhodothermus and Bacteroides. Finally, the Alphaproteobacteria Rhodospirillum was also important.In spite of the differences at the taxonomic level, functionally the two mats were similar. Thus, similarroles could be fulfilled by different organisms. For example, primary production, performed mainly byphotosynthetic organisms from the phyla Cyanobacteria and Chloroflexi in Brava, is performed bymembers of Alphaproteobacteria in Tebenquiche.Further comparison with other microbial mats will allow identifying unique genes from theseenvironments related to their extreme characteristics.