Laguna Negra Research Articles

Completed genome segments of Maciel, Lechiguanas, and Laguna Negra orthohantaviruses.

New World orthohantaviruses are rodent-borne tri-segmented viruses that cause hantavirus cardiopulmonary syndrome in humans in the Americas. Molecular diagnostics for orthohantaviruses can be improved with more sequence data. Reported here are completed genomes for Lechiguanas, Maciel, and Laguna Negra viruses.

CITIZEN PARTICIPATION FOR THE MONITORING AND INTEGRAL VALUATION DESTINATION: THE CASE OF THE LAGUNA NEGRA WETLAND IN COLOMBIA

This study was conducted in the Laguna Negra wetland located in Villamaría, Caldas, Colombia, in order to determine indicators for monitoring, the integral valuation in the wetland and support its conservation. The dynamics of the water mirror was analyzed, finding that between the years 2015 - 2019 it had an increase, which is reported to the community to generate a space for citizen participation and to know their opinions on the ecosystem services of the same. An analysis of the carrying capacity was also conducted, obtaining a real carrying capacity of 5.5 people per day simultaneously. The ecosystem services were defined by the community living near the wetland, based on a participatory methodology. On the other hand, to calculate the WTP for the conservation of the site, an instrument was applied to the tourists, the results of which allowed a valuation of the cost of the trip and a contingent valuation considering the WTP. With the results of the instrument and the application of an econometric model, a model was proposed to calculate the probability of success associated with WTP, which according to the model is directly related to educational level and socioeconomic stratum.

Campo del Cielo modeling and comparison with observations: II. Funnels and craters

AbstractThe Campo del Cielo impact structure exhibits several penetration funnels and impact craters. Here, we model the formation of these funnels with pre‐impact conditions consistent with the results of meteoroid entry models. We study vertical impacts to find the dependence of funnel geometry (depth, diameter) on impact velocity and target porosity. At velocities above 1 km s−1, we observe strong deformation of the projectile and transformation of funnels into regular impact craters. We also use 3‐D impact models to study oblique impacts and find that in the case of impact angles <25° to the horizon, the projectile bounces off the target. Instead of a funnel, an elongated groove forms, while the fragmented projectile escapes and moves farther downrange. At steeper impact angles, funnels form with the projectile at its tip. Early interpretations of the Campo del Cielo impact angle at 9–10° were based on (i) an oversimplified atmospheric model allowing “correct” strewn field elongation and (ii) the results of excavation in which the sloping boundary between breccia‐like materials and infilling loess was interpreted as a true crater floor and its slope was equated to the impact angle. As our models show, the projectile trajectory within the target is not a straight line, and the angle to horizon changes from a steep one at the impact point to zero and then to a negative value (the projectile is moving upward). We also model two impact craters (Hoyo de la Cañada and Laguna Negra) created by high‐velocity fragments to demonstrate the projectile remnants ricochet in the downrange direction.

Caracterización limnológica, estructura del fitoplancton y batimetría de Laguna Negra, un lago coloreado del Parque Nacional Tierra del Fuego (Argentina)

The 4% of the Argentinian sector from Tierra del Fuego is covered with water. Colored lakes are among the most conspicuous water bodies in the Andean area, and Laguna Negra, in the National Park Tierra del Fuego, is one of them. The main physical and chemical variables were monitored and phytoplankton samples were obtained with a monthly frequency during the ice-free period, between September 2016 and March 2018 (n=15). Laguna Negra was deeper than expected, with a maximum depth of 15.5 m. In addition, this lake has high pH values (7.5±0.55), which were quite stable during the study (variation coefficient, VC=8.3%). These characteristics preclude us from considering this lake as a shallow peatland lake. Dissolved and total nutrients were low and did not show a temporal pattern of fluctuation during the study period. The same trend of no clear fluctuation was also shared by dissolved organic carbon concentration (DOC=7.7±0.78 mg/L). Taxa richness ranged between 6 and 13 throughout the study. The biovolume was inversely correlated with the vertical attenuation coefficient of light (Kd). Phytoplankton biomass (chlorophyll-a concentration, abundance, and biovolume) was generally low, with Dinobryon divergens, Mallomonas sp. and Parvodinium cf. inconspicuum being the dominant taxa. Depending on the classification used, Laguna Negra might be regarded as a humic or dystrophic lake because its color is at the edge of values used in the current literature to consider a lake as humic.

Geospatial insights into the controls of microbialite formation at Laguna Negra, Argentina.

Microbialites provide a record of the interaction of microorganisms with their environment constituting a record of microbial life and environments through geologic time. Our capacity to interpret this record is limited by an incomplete understanding of the microbial, geochemical, and physical processes that influence microbialite formation and morphogenesis. The modern system Laguna Negra in Catamarca Province, Argentina contains microbialites in a zone of carbonate precipitation associated with physico-chemical gradients and variable microbial community structure, making it an ideal location to study how these processes interact to drive microbialite formation. In this study, we investigated the geospatial relationships between carbonate morphology, geochemistry, and microbial community at the macro- (decimeter) to mega- (meter) scale by combining high-resolution imagery with field observations. We mapped the distribution of carbonate morphologies and allochtonously-derived volcaniclasts and correlated these with sedimentary matrices and geochemical parameters. Our work shows that the macroscale distribution of different carbonate morphologies spatially correlates with microbial mat distributions-a result consistent with previous microscale observations. Specifically, microbialitic carbonate morphologies more commonly occur associated with microbial mats while abiotically derived carbonate morphologies were less commonly associated with microbial mats. Spatial variability in the size and abundance of mineralized structures was also observed, however, the processes controlling this variability remains unclear and likely represent a combination of microbial, geochemical, and physical processes. Likewise, the processes controlling the spatial distribution of microbial mats at Laguna Negra are also unresolved. Our results suggest that in addition to the physical drivers observed in other modern environments, variability in the spatial distribution of microbialites and other carbonate morphologies at the macro- to megascale can be controlled by microbial processes. Overall, this study provides insight into the interpretation of microbialite occurrence and distributions in the geologic record and highlights the utility of geospatial statistics to probe the controls of microbialite formation in other environments.

Community Vertical Composition of the Laguna Negra Hypersaline Microbial Mat, Puna Region (Argentinean Andes).

Simple SummaryThe Laguna Negra is a high-altitude hypersaline lake located in the Puna region in Argentina, hosting microbial mats and modern stromatolites, microbially formed rocks found throughout the geological record. Some recent studies have shown the relevance of the lakes in this region for (i) the discovery of new extremophiles, particularly those tolerant to high UV and, furthermore, (ii) the study of biosignatures in stromatolites. In this work, a detailed survey, layer by layer, of the microbial diversity of the most widespread microbial mat in the Laguna Negra was reported, to unravel the spatial arrangement of the microbial community. The results reveal the vertical distribution of the main prokaryotic microbial taxa, and underline abundant Deinococcus-Thermus at the top of the microbial mat with high amounts of deinoxanthin, which may help the total community to cope with high UV radiation. This study allows a better understanding of the community strategies to thrive under environmental stressors in the Laguna Negra and its counterparts in the Altiplano-Puna region. The Altiplano-Puna region is a high-altitude plateau in South America characterized by extreme conditions, including the highest UV incidence on Earth. The Laguna Negra is a hypersaline lake located in the Catamarca Province, northwestern Argentina, where stromatolites and other microbialites are found, and where life is mostly restricted to microbial mats. In this study, a particular microbial mat that covers the shore of the lake was explored, to unravel its layer-by-layer vertical structure in response to the environmental stressors therein. Microbial community composition was assessed by high-throughput 16S rRNA gene sequencing and pigment content analyses, complemented with microscopy tools to characterize its spatial arrangement within the mat. The top layer of the mat has a remarkable UV-tolerance feature, characterized by the presence of Deinococcus-Thermus and deinoxanthin, which might reflect a shielding strategy to cope with high UV radiation. Chloroflexi and Deltaproteobacteria were abundant in the second and third underlying layers, respectively. The bottom layer harbors copious Halanaerobiaeota. Subspherical aggregates composed of calcite, extracellular polymeric substances, abundant diatoms, and other microorganisms were observed all along the mat as the main structural component. This detailed study provides insights into the strategies of microbial communities to thrive under high UV radiation and hypersalinity in high-altitude lakes in the Altiplano-Puna region.

Arsenic in natural carbonates: The role of the biogeochemical conditions in its solid speciation

The interaction of geogenic arsenic (As) with carbonate minerals depends on the biological and geochemical conditions of the environment. This study sheds light on how different environmental conditions influence the carbonate mineral formation and the interaction with As. Three different samples were analyzed: carbonates associated with thermal springs, oncolites and a soil carbonate sample. Synchrotron-based XAS was used to evaluate the As solid speciation while micro-focused XPS analysis was performed to determine the surface speciation of Fe and S. Chemical and mineralogical characterization were performed using conventional techniques.The results revealed that the calcium carbonates minerals are a consequence of the environmental chemical composition (Sr2+, Mg2+ and arsenate), although physical factors (i.e., temperature) and the influence of microorganisms could not be ruled out. These conditions, identified in thermal springs samples and oncolites, determine the precipitation of aragonite, calcite and Sr/Mg-rich calcite and the inclusion of As(V)/(III) within crystal lattice. As(III) could be a product of the arsenate reduction by microbial activities. Conversely, in the soil carbonate sample, As(V) is adsorbed onto calcite. In addition, the As(1-) species was determined in one sample from Laguna Negra; this species likely corresponds to an As-bearing sulfide compound (i.e., arsenian pyrite).

BILOGÍA FÍLMICA MACHADIANA: LA SOMBRA DE CAÍN SOBRE LA ¡HERMOSA TIERRA DE ESPAÑA!

Resumen: Ya superado el octogésimo aniversario del fallecimiento de Antonio Machado, volvemos nuestra mirada hacia dos películas cuyos discursos gravitan sobre una honda inmersión en su obra y su personalidad. Dirigidas por Arturo Ruiz-Castillo entre el verano de 1952 y la primavera de 1953, La laguna negra surge como transposición de un romance del poeta sevillano, mientras que el relato posbélico de Dos caminos parece nutrirse de una tupida invocación alegórica del pensamiento machadiano. Escasamente conocidos y apenas considerados por la historiografía cinematográfica, ambos filmes conforman una inconfesa bilogía dotada de una insólita densidad semántica que urge reivindicar.Abstract: Just after the eightieth anniversary of death of Antonio Machado, we turn our attention to two films whose speeches gravitate a deep immersion in his work and his personality. Directed by Arturo Ruiz- Castillo between the summer of 1952 and the spring of 1953, La laguna negra emerges as transposition of a romance of the Sevillian poet, while the post-war account Dos caminos seem to be nourished by a dense allegorical invocation of Machadian thought. Scarcely known and barely considered by historiography film, both films make up an unmistakable biology with an unusual semantic density that needs to be vindicated urgently.

Molecular characterization of novel Ehrlichia genotypes in Ixodes auritulus from Uruguay

Ehrlichia are small intracellular Gram-negative bacteria transmitted by ticks. These microorganisms cause ehrlichiosis, a complex of life-threatening emerging zoonoses and diseases of global veterinary relevance. The aim of this study was to investigate the presence of Ehrlichia in free-living Ixodes auritulus collected in Uruguay. Ticks were collected from vegetation in five localities from the southeast and northeast of the country between 2014 and 2017. Detection of Ehrlichia DNA was performed in pools of adults or nymphs grouped according to the collection site and date. A total of 1,548 I. auritulus ticks were collected in four of the five locations sampled. Fragments of three loci (16S rRNA, dsb and groEL) were obtained by PCR, and phylogenies inferred using Bayesian inference analysis for each gene independently. DNA of Ehrlichia spp. was found in 15 out of 42 tick pools. Based on the topology of the phylogenetic trees, our sequences represent two novel genotypes for the genus named as Ehrlichia sp. Serrana and Ehrlichia sp. Laguna Negra. Both genotypes were closely related to Ehrlichia sp. Magellanica, a species detected in Ixodes uriae and Magellanic penguins. Considering that all stages of I. auritulus and I. uriae are parasites of birds, their phylogenetic relationships, and common eco–epidemiological profiles, it is reasonable to state that these genotypes of Ehrlichia spp. may represent a natural group likely associated with birds. Our results constitute the first characterization of Ehrlichia spp. in Uruguay. Future studies on birds reported as hosts for I. auritulus are needed to further understand the epidemiological cycles of both Ehrlichia genotypes in the country. Finally, I. auritulus does not feed on humans, so the two Ehrlichia species reported herein might have no implications in human health.

Phenotypic and genetic differentiation between diadromous and landlocked puyen Galaxias maculatus.

This study reports the phenotypic and genetic differences between individuals of puyen Galaxias maculatus from two sites in the same river basin in Tierra del Fuego National Park, southern South America. Individuals from the two sampling sites presented morphometric and genetic differences. The morphometric differences indicated that individuals from Laguna Negra (LN) were short and more robust and had large eyes, whereas those from Arroyo Negro (AN) were thin and elongated and had small eyes. Genetic differences showed that AN individuals had a greater genetic structuration and an older demographic history than LN individuals. The results of this study affirmed that the individuals from the two sampling sites belong to different populations with a high degree of isolation. The demographic history could indicate that the individuals of G. maculatus which migrated to northern areas during the last glaciation settled in the Beagle Channel after its formation. The LN population could have originated after the retreat of the glaciers, migrating from AN.

Controls of extreme isotopic enrichment in modern microbialites and associated abiogenic carbonates

Microbialites and abiogenic carbonates of the closed-basin hypersaline lake Laguna Negra (Catamarca Province, Argentina) are highly enriched in both 13C and 18O. These carbonates precipitate in the zone of recharge where lake water mixes with groundwater. We examined the processes controlling the isotopic evolution of input waters in order to better interpret the isotopic compositions of the carbonates. Large enrichments of 13C in dissolved inorganic carbon and 18O in water occur as input groundwater chemically evolves. These enrichments can be explained through the abiotic processes of water-equilibration, evaporation, degassing, and carbonate precipitation. The 13C and 18O contents of lake carbonates are consistent with equilibrium precipitation from lake water indicating that the currently ongoing processes can explain the isotopic patterns observed in carbonates. Isotopic compositions of these microbialites are largely unrelated to the biological processes controlling microbialite formation – a pattern that may be generalizable to other settings. However, the isotopic compositions of these microbialites record information about their depositional environment.

A Test in a High Altitude Lake of a Multi-Parametric Rapid Methodology for Assessing Life in Liquid Environments on Planetary Bodies: A Potential New Freshwater Polychaete Tubeworm Community

On our planet, aqueous environments such as deep sea or high-altitude aphotic lakes, subject to present or past volcanic activity and active deglaciation, may provide analogues to the aqueous environments found on such planetary bodies as Europa, Titan or Enceladus. We report here methodologies and technologies tested in Laguna Negra, a high altitude lake in the Central Andes, Chile, for exploring and assessing the presence of life within planetary lakes or interior oceans. We adopted a multi-parametric Rapid Ecological Assessment (REA) approach centered around collecting video imagery (by an Underwater Imaging System) and sampling benthic sediments (for sedimentological, biological and geochemical analysis) to depths of 272 m, to complement physico-chemical sampling of the water column and collection of shallow sediments for microbiological analysis (reported in separate publications). This enabled us to classify and assess the apparent status of benthic habitats, based on substrata and environmental characteristics, together with floral and faunal community characteristics and bioturbation artifacts. Videos imagery showed that the lower water column was characterized by a variably intense sestonic flux of particles and debris among which were planktonic organisms such as ostracods, copepods and possibly cladocerans. Sediment analysis revealed at all depths abundant diatom frustules, mainly of an acidophile pennade diatom Pinnularia acidicola, amid vegetal debris likely originating from littoral macrophytes. Video imagery showed that the lakebed was partly covered by microbial mats and depositional matter and harboured an unexpectedly rich assortment of macrofauna, including sponges, tubificid worms, flatworms, bivalves and crustaceans. Various forms of bioturbation were also encountered, some with the animals in the tracks. Most notably, at the deepest site, a previously undescribed faunal feature was evident, apparently formed by a mat-like community of several layers of what appeared to be polychaete tubeworms, possibly of the family Siboglinidae. It is hypothesized that the hydrothermal activity observed in the region may supply the compounds able to support the deep-water microrganisms from which such tubeworms typically gain sustenance. Such processes could be present on other deep and aphotic liquid-water-bearing planetary bodies.

Microbiology and Nitrogen Cycle in the Benthic Sediments of a Glacial Oligotrophic Deep Andean Lake as Analog of Ancient Martian Lake-Beds.

Potential benthic habitats of early Mars lakes, probably oligotrophic, could range from hydrothermal to cold sediments. Dynamic processes in the water column (such as turbidity or UV penetration) as well as in the benthic bed (temperature gradients, turbation, or sedimentation rate) contribute to supply nutrients to a potential microbial ecosystem. High altitude, oligotrophic, and deep Andean lakes with active deglaciation processes and recent or past volcanic activity are natural models to assess the feasibility of life in other planetary lake/ocean environments and to develop technology for their exploration. We sampled the benthic sediments (down to 269 m depth) of the oligotrophic lake Laguna Negra (Central Andes, Chile) to investigate its ecosystem through geochemical, biomarker profiling, and molecular ecology studies. The chemistry of the benthic water was similar to the rest of the water column, except for variable amounts of ammonium (up to 2.8 ppm) and nitrate (up to 0.13 ppm). A life detector chip with a 300-antibody microarray revealed the presence of biomass in the form of exopolysaccharides and other microbial markers associated to several phylogenetic groups and potential microaerobic and anaerobic metabolisms such as nitrate reduction. DNA analyses showed that 27% of the Archaea sequences corresponded to a group of ammonia-oxidizing archaea (AOA) similar (97%) to Nitrosopumilus spp. and Nitrosoarchaeum spp. (Thaumarchaeota), and 4% of Bacteria sequences to nitrite-oxidizing bacteria from the Nitrospira genus, suggesting a coupling between ammonia and nitrite oxidation. Mesocosm experiments with the specific AOA inhibitor 2-Phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) demonstrated an AOA-associated ammonia oxidation activity with the simultaneous accumulation of nitrate and sulfate. The results showed a rich benthic microbial community dominated by microaerobic and anaerobic metabolisms thriving under aphotic, low temperature (4°C), and relatively high pressure, that might be a suitable terrestrial analog of other planetary settings.

PLAGUICIDAS ORGANOCLORADOS EN AGUA DE LA LAGUNA NEGRA DE PUERTO MARQUÉS, ACAPULCO, GUERRERO, MÉXICO

The presence of organochlorine pesticides in aquatic systems is an issue of vital importance, because it affects non-renewable natural resources and as consequence the quality of water for organisms that live and use this resource. Coastal lagoons are aquatic systems that receive a large amount of organic matter and organic (petroleum hydrocarbons and pesticides) and inorganic (heavy metals) pollutants, where the biogeochemical and biological cycles of many species of commercial interest are carried out, as well as tourism activities. The objective of the present work was to quantify the concentrations of organochlorine pesticides in the water of the Laguna Negra of Puerto Marques, Acapulco. The organochlorine compounds were determined by gas chromatography analysis with electron capture detector ( 63 Ni). The results obtained in the sampling sites were divided into lagoon and discharge sites and did not show a significant difference, since the total average concentrations were 5.55 and 6.02 μg/L, respectively. It was also noted that during the dry season a total average of 6.80 μg/L was recorded, while in the rainy season it was 3.56 μg/L. According to the Official Mexican Standard NOM-SSA1-1994 there should be no organochlorine pesticides. Although concentrations are low (μg/L), they can cause some alteration to organisms through bioaccumulation and biomagnification with risks to the health of the natural system and the human being.

Mineralized microbialites as archives of environmental evolution, Laguna Negra, Catamarca Province, Argentina.

Environmental fluctuations are recorded in a variety of sedimentary archives of lacustrine depositional systems. Geochemical signals recovered from bottom sediments in closed-basin lakes are among the most sensitive paleoenvironmental indicators and are commonly used in reconstructing lake evolution. Microbialites (i.e., organosedimentary deposits accreted through microbial trapping and binding of detrital sediment or in situ mineral precipitation on organics [Palaios, 2, 1987, 241]), however, have been largely overlooked as paleoenvironmental repositories. Here, we investigate concentrically laminated mineralized microbialites from Laguna Negra, a high-altitude (4,100m above sea level) hypersaline, closed-basin lake in northwestern Argentina, and explore the potential for recovery of environmental signals from these unique sedimentary archives. Spatial heterogeneity in hydrological regime helps define zones inside Laguna Negra, each with their own morphologically distinct microbialite type. Most notably, platey microbialites (in Zone 3A) are precipitated by evaporative concentration processes, while discoidal oncolites (in Zone 3C) are interpreted result from fluid mixing and biologically mediated nucleation. This spatial heterogeneity is reflected in petrographically distinct carbonate fabrics: micritic, botryoidal, and isopachous. Fabric type is interpreted to reflect a combination of physical and biological influences during mineralization, and paired C-isotope measurement of carbonate and organic matter supports ecological differences as a dominant control on C-isotopic evolution between zones. Laminae of Laguna Negra microbialites preserve a range of δ13 Ccarb from +5.75‰ to +18.25‰ and δ18 Ocarb from -2.04‰ to +9.28‰. Temporal trends of lower carbon and oxygen isotopic compositions suggest that the influence of CO2 degassing associated with evaporation has decreased over time. Combined, these results indicate that microbialite archives can provide data that aid in interpretation of both lake paleohydrology and paleoenvironmental change.

Fragilariaceae (Bacillariophyta) en humedales de altura de Catamarca (Argentina).

Se estudiaron tres humedales de alta montaña en la provincia de Catamarca, Argentina, como parte de un estudio más amplio que se enfoca en cuerpos de agua en los Andes argentinos. En esta contribución damos a conocer dentro del grupo de Fragilariaceae de pequeño tamaño, especies de los géneros Staurosira, Staurosirella y Pseudostaurosira halladas en las lagunas Diamante (hiperhalina) y Salitre (dulce) y en la vega de la laguna Negra (mesohalina). De las especies encontradas, Staurosirella galanensis, S. salitrensis y Pseudostaurosira ferrarioae son nuevas para la ciencia y fueron descritas, ilustradas y comparadas con taxones similares. S. galanensis es más pequeña y romboidal que otras especies cruciformes del género, mientras que S. salitrensis es de menor tamaño y menos silicificada que otras especies estrechamente relacionadas. Pseudostaurosira ferrarioae se distingue de especies afines especialmente por tener campos de poros apicales bien desarrollados. Los otros representantes de esta familia encontrados en el área de estudio fueron Staurosira binodis, especie que se menciona por primera vez para Catamarca, Pseudostaurosira altiplanensis, citada por primera vez para Argentina y P. aff. polonica.

Rivularia halophila sp. nov. (Nostocales, Cyanobacteria): the first species of Rivularia described with the modern polyphasic approach

ABSTRACTNatural populations of a Rivularia-like cyanobacterium were collected from the carbonate deposits of the temporarily flooded littoral zone of a hypersaline, high elevation lake, The Laguna Negra, Andes, Argentina. Subsequently, the cyanobacterial strain PUNA-NP3, named after its origin (Puna Volcanic Plateau) was isolated from these Rivularia-like rounded, pillow-like, black microbial mats. None of the previously described species of the genus Rivularia occupy inland, hypersaline aquatic environments. After morphological examination of this strain, we found clear morphological autapomorphies, such as mucilaginous pads at the bases of the young trichomes, wide trichomes and filaments, and uniquely branched trichomes. Furthermore, based on results from 16S rRNA phylogeny and analysis of the 16S-23S ITS region, PUNA-NP3 was found to be an independent lineage of the evolutionary tree. Based on the combination of ecological, morphological and molecular evidence, we name strain PUNA-NP3 Rivularia halophila sp. nov. a new species under requirements of the International Code of Nomenclature for Algae, Fungi and Plants.

Calcium Carbonate Precipitation in Diatom-rich Microbial Mats: The Laguna Negra Hypersaline Lake, Catamarca, Argentina

Abstract Carbonate microbialites provide a window to understand microbe–mineral interactions in modern environments and in the geological record. Unraveling microbial versus physicochemical controls and biogeochemical signatures is not always straightforward. Environmental and laboratory studies have shown that microbial activity can play a central role in calcium carbonate precipitation. Most studies have focused on the effects of Bacteria and Archaea activity on carbonate precipitation processes (e.g., cyanobacteria, sulfate-reducing bacteria, sulfide-oxidizing bacteria and iron-reducing bacteria). The influence of eukaryotic activity, such as diatoms and other microalgae, on carbonate precipitation and microbialite formation has been the focus of less attention. This study explores carbonate mineralization in active diatom-rich microbial mats developed in a high-altitude groundwater-fed hypersaline lake in the Puna region of Catamarca, Argentina. Previous work has focused on the texture, mineralogy, and stable-isotope chemistry of the subfossil oncoidal and laminar microbialites. Here, using 16S rDNA Bacteria diversity analysis, confocal scanning laser microscopy, scanning electron microscopy, and transmitted-light microscopy, we explore the Bacteria and diatom diversity in the microbial mats and the related carbonates textures and make comparisons with similar textures in the associated oncoidal microbialites. Diatom-rich subspherical aggregates, which have not been previously described in the literature, show a diverse microbial community with abundant exopolymeric substances (EPSs) where carbonate precipitation takes place. These aggregates are a main component of the Laguna Negra microbial mats and show anhedral micritic calcite in the EPS matrix as the main mineral component. Similar calcite micrite textures are also preserved as one lamina type in the associated oncoids. On the other hand, where EPS are absent, carbonate precipitation, related to pennate diatom blooms, is represented by euhedral aragonite needles suggesting different mechanisms and controls. Changes in the microbial communities are recorded in the oncoids as different lamina types, providing a link between the currently active mats and the subfossil oncoidal structures. This is a first survey of these previously unexplored diatom-rich microbial mats developed under extreme environmental conditions in the Laguna Negra. Understanding the effect that the interaction between diatoms and prokaryotic communities has on carbonate precipitation may provide some insight on the evolution of microbialite textures and fabrics, and on the change from prokaryote-dominated systems to mixed eukaryotic–prokaryotic systems.

Characterization of Pustular Mats and Related Rivularia-Rich Laminations in Oncoids From the Laguna Negra Lake (Argentina).

Stromatolites are organo-sedimentary structures that represent some of the oldest records of the early biosphere on Earth. Cyanobacteria are considered as a main component of the microbial mats that are supposed to produce stromatolite-like structures. Understanding the role of cyanobacteria and associated microorganisms on the mineralization processes is critical to better understand what can be preserved in the laminated structure of stromatolites. Laguna Negra (Catamarca, Argentina), a high-altitude hypersaline lake where stromatolites are currently formed, is considered as an analog environment of early Earth. This study aimed at characterizing carbonate precipitation within microbial mats and associated oncoids in Laguna Negra. In particular, we focused on carbonated black pustular mats. By combining Confocal Laser Scanning Microscopy, Scanning Electron Microscopy, Laser Microdissection and Whole Genome Amplification, Cloning and Sanger sequencing, and Focused Ion Beam milling for Transmission Electron Microscopy, we showed that carbonate precipitation did not directly initiate on the sheaths of cyanobacterial Rivularia, which dominate in the mat. It occurred via organo-mineralization processes within a large EPS matrix excreted by the diverse microbial consortium associated with Rivularia where diatoms and anoxygenic phototrophic bacteria were particularly abundant. By structuring a large microbial consortium, Rivularia should then favor the formation of organic-rich laminations of carbonates that can be preserved in stromatolites. By using Fourier Transform Infrared spectroscopy and Synchrotron-based deep UV fluorescence imaging, we compared laminations rich in structures resembling Rivularia to putatively chemically-precipitated laminations in oncoids associated with the mats. We showed that they presented a different mineralogy jointly with a higher content in organic remnants, hence providing some criteria of biogenicity to be searched for in the fossil record.

Watershed-Induced Limnological and Microbial Status in Two Oligotrophic Andean Lakes Exposed to the Same Climatic Scenario.

Laguna Negra and Lo Encañado are two oligotrophic Andean lakes forming part of the system fed by meltwater from distinct glacial tongues of the Echaurren glacier in central Chile, which is in a recession period. The recent increase in temperature and decline in precipitation have led to an increase of glacial meltwater and sediments entering these lakes. Although the lacustrine systems are also hydrogeologically connected, the limnology of the lakes is strongly controlled by the surface processes related to the respective sub-watersheds and hydrology. Watershed characteristics (area and length, slope, lithology, resistance to erosion, among others) affect the chemical and physical characteristics of both lakes (e.g., nutrient concentration and turbidity). We studied physical and chemical variables and performed 16S rRNA amplicon sequencing to determine the specific microbial signature of the lakes. The transparency, temperature, turbidity and concentrations of chlorophyll-a, dissolved organic matter, nutrients and the total number of cells, revealed the different status of both lakes at the time of sampling. The predominant bacterial groups in both lakes were Proteobacteria, Verrucomicrobia, and Bacteroidetes. Interestingly, the contribution of phototrophs was significantly higher in LN compared to LE (13 and 4% respectively) and the major fraction corresponded to Anoxygenic Phototrophs (AP) represented by Chloroflexi, Alpha, and Betaproteobacteria. Multivariate analyses showed that the nutrient levels and the light availability of both lakes, which finally depend on the hydrological characteristics of the respective watersheds, explain the differential community composition/function. The abundance of a diverse photoheterotrophic bacterioplankton community suggests that the ability to utilize solar energy along with organic and inorganic substrates is a key function in these oligotrophic mountain lakes.