Lake Pastos Grandes
Lake Pastos Grandes in Bolivia is mainly composed of salt flats, which are sporadically and only partially submerged during the wet season.  The lake has attracted attention for tourism as well as mineral extraction. Human activities can have severe negative impacts on lakes, for instance, by propagating pathogens with resistance to different antibiotics or altering the amount of bioavailable nitrogen. The chemical composition of water samples of the lake and some influent rivers was determined. We found that it is likely that the lake was influenced by the dilution of metals from ancient evaporites. We performed the first metagenomic studies on this lake. Analyses on shotgun metagenomics revealed that the relative abundances of Burkholderiales and Pseudomonadales were noteworthy in the water samples, whereas the archaea belonging to the Halobacteriales and Cyanobacteria from subsection III had high abundances in the salt flat. The eukaryotes Crustacea and Diatomea exhibited the highest abundances in the water samples. The diatoms Navicula spp. and Nitzschia spp. were detected, as in 1978, and may be used as bioindicators. Moreover, genes in the metagenomes were utilized to construct the N-cycle of the lake as a baseline to monitor the effect of environmental fluctuations in the lake, thus preventing its pollution by external sources. Genes related to cell biosynthesis (glnA, gs K00266, asnB), nitronate monooxygenase (nmo), and dissimilatory (nirD) or assimilatory (nasA) nitrate reduction had the highest relative abundances in the N-cycle. Additionally, rifamycin resistance genes (rpoB2, rpoB) and genes related to efflux pumps, which are not considered a hazard when identified in metagenomes, had the uppermost relative abundances in all sampling points. We found that Lake Pastos Grandes hitherto does not show an appreciable influence by anthropogenic actions.