Microbial Diversity in Sediment Ecosystems (Evaporites Domes, Microbial Mats, and Crusts) of Hypersaline Laguna Tebenquiche, Salar de Atacama, Chile

We combined nucleic acid-based molecular methods, biogeochemical measurements, and physicochemical characteristics to investigate microbial sedimentary ecosystems of Laguna Tebenquiche, Atacama Desert, Chile. Molecular diversity, and biogeochemistry of hypersaline microbial mats, rhizome-associated concretions, and an endoevaporite were compared with: The V4 hypervariable region of the 16S rRNA gene was amplified by pyrosequencing to analyze the total microbial diversity (i.e., bacteria and archaea) in bulk samples, and in addition, in detail on a millimeter scale in one microbial mat and in one evaporite. Archaea were more abundant than bacteria. Euryarchaeota was one of the most abundant phyla in all samples, and particularly dominant (97% of total diversity) in the most lithified ecosystem, the evaporite. Most of the euryarchaeal OTUs could be assigned to the class Halobacteria or anaerobic and methanogenic archaea

Mercury contamination and cycling in the coastal zone

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Spirochetes et géochimie des tapis microbiens de marais salants : Implications pour l'enregistrement fossile

Les tapis microbiens sont des associations microbiennes agissant en synergie par le biais desquelles les éléments majeurs tels que le soufre sont recyclés au travers de processus microbiens et géologiques. Les variations de pH, de l'O2, des sulfures, des substances exopolymériques (EPS) et du taux de réduction des sulfates ont été mesurées en fonction de la profondeur dans un tapis microbien marin dominé par une Oscillatoria sp. et des Microcoleus, tapis localisé dans les marais salants de Great Sippewissett, Massachusetts. De plus, des mesures de l'enrichissement de spirochètes ainsi que des cultures de Spirochaetae litoralis ont mis en évidence la consommation des sulfures et la production concomitante de polysulfures, de thiosulfate et probablement aussi de sulfates. Ces données suggèrent que les spirochètes peuvent jouer un rôle dans le cycle du soufre dans ces tapis microbiens. Les spirochètes, qui sont des organismes obligatoirement ou facultativement anaérobies, pourraient utiliser les sulfures pour éliminer l'oxygène de leur environnement. Ainsi les spirochètes pourraient aussi favoriser la préservation des tapis microbiens dans l'enregistrement sédimentaire en dégradant les EPS et en libérant des composés organiques de faible poids moléculaire (LMWOC). L'oxydation des sulfures (c'est-à-dire suppression de l'oxygène) et la dégradation des EPS (c'est-à-dire la production de matériaux de faible poids moléculaire) stimulent tous deux l'activité des bactéries sulfato-réductrices (SRB) qui sont responsables de la précipitation du carbonate de calcium dans la plupart des tapis microbiens en cours de lithification.Microbial mats are synergistic microbial consortia through which major elements, including sulfur, are cycled due to microbial and geological processes. Depth profiles of pH, O2, sulfide, exopolymeric substances (EPS), and the rate of sulfate reduction were determined in an Oscillatoria sp. and Microcoleus-dominated marine microbial mat at the Great Sippewissett salt marsh, Massachusetts. In addition, measurements in spirochete enrichments and Spirochaetae litoralis cultures showed sulfide consumption during which polysulfides, thiosulfate, and presumably sulfate formed. These data suggest that spirochetes can play a role in the cycling of sulfur in these mats. The obligate to facultative anaerobic spirochetes may consume sulfide to remove oxygen. Furthermore, spirochetes may enhance preservation of microbial mats within the rock record by degrading EPS and producing low molecular weight organic compounds (LMWOC). Both sulfide oxidation (i.e., oxygen removal) and EPS degradation (i.e., production of LMW organic compounds) stimulate the activity of sulfate-reducing bacteria (SRB), which are responsible for the precipitation of calcium carbonate in most lithifying mats

Production and cycling of natural microbial exopolymers (EPS) within a marine stromatolite

Abstract Extracellular polymeric secretions (EPS) that are produced by cyanobacteria represent potential structuring agents in the formation of marine stromatolites. The abundance, production, and degradation of EPS in the upper layers of a microbial mat forming shallow subtidal stromatolites at Highborne Cay, Bahamas, were determined using 14 C tracer experiments and were integrated with measurements of other microbial community parameters. The upper regions of a Type 2 [Reid, R.P., Visscher, P.T., Decho, A.W., Stolz, J., Bebout, B., MacIntyre, I.G., Dupraz, C., Pinckney, J., Paerl, H., Prufert-Bebout, L., Steppe, T., Des Marais, D., 2000. The role of microbes in accretion, lamination and early lithification of modern marine stromatolites. Nature (London) 406, 989-992] stromatolite mat exhibited a distinct layering of alternating bgreenQ cyanobacteria-rich layers (Layers 1 and 3) and bwhiteQ layers (Layers 2 and 4), and the natural abundance of EPS varied significantly depending on the mat layer. The highest EPS abundance occurred in Layer 2. The production of new EPS, as estimated by the incorporation of 14 C-bicarbonate into EPS, occurred in all layers examined, with the highest production in Layer 1 and during periods of photosynthesis (i.e., daylight hours). A large pool (i.e., up to 49%) of the total 14 Cbicarbonate uptake was released as low molecular-weight (MW) dissolved organic carbon (DOC). This DOC was rapidly mineralized to CO 2 by heterotrophic bacteria. EPS degradation, as determined by the conversion of 14 C-EPS to 14 CO 2 , was slowest in Layer 2. Results of slurry experiments, examining O 2 uptake following additions of organic substrates, including EPS, supported this degradation trend and further demonstrated selective utilization by heterotrophs of specific monomers, such as acetate, ethanol, and uronic acids. Results indicated that natural EPS may be rapidly transformed post-secretion by heterotrophic degradation, specifically by sulfate-reducing bacteria, to a more-refractory remnant polymer that is relatively slow to accumulate. A mass balance analysis suggested that a layer-specific pattern in EPS and low-MW DOC turnover may contribute to major carbonate precipitation events within stromatolites. Our findings represent the first estimate of EP

Characteristics and turnover of exopolymeric substances in a hypersaline microbial mat

The properties and microbial turnover of exopolymeric substances (EPS) were measured in a hypersaline nonlithifying microbial mat (Eleuthera, Bahamas) to investigate their potential role in calcium carbonate (CaCO3) precipitation. Depth profiles of EPS abundance and enzyme activities indicated that c. 80% of the EPS were turned over in the upper 15-20 mm. Oxic and anoxic mat homogenates amended with low-molecular-weight (LMW) organic carbon, sugar monomers, and different types of EPS revealed rapid consumption of all substrates. When comparing the consumption of EPS with that of other substrates, only marginally longer lag times and lower rates were observed. EPS (5-8%) were readily consumed during the conversion of labile to refractory EPS. This coincided with a decrease in glucosidase activity and a decrease in the number of acidic functional groups on the EPS. Approximately half of the calcium bound to the EPS remained after 10 dialyses steps. This tightly bound calcium was readily available to precipitate as CaCO3. We present a conceptual model in which LMW organic carbon complexed with the tightly bound calcium is released upon enzyme activity. This increases alkalinity and creates binding sites for carbonate and allows CaCO3 to precipitate. Therefore, this model explains interactions between EPS and CaCO3 precipitation, and underscores the critical role of aerobic and anaerobic microorganisms in early diagenesis and lithification processe

Active eukaryotes in microbialites from Highborne Cay, Bahamas, and Hamelin Pool (Shark Bay), Australia

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in The ISME Journal 8 (2014): 418–429, doi:10.1038/ismej.2013.130.Microbialites are organosedimentary structures that are formed through the interaction of benthic microbial communities and sediments and include mineral precipitation. These lithifying microbial mat structures include stromatolites and thrombolites. Exuma Sound in the Bahamas, and Hamelin Pool in Shark Bay, Western Australia are two locations where significant stands of modern microbialites exist. Although prokaryotic diversity in these structures is reasonably well documented, little is known about the eukaryotic component of these communities and their potential to influence sedimentary fabrics through grazing, binding and burrowing activities. Accordingly, comparisons of eukaryotic communities in modern stromatolitic and thrombolytic mats can potentially provide insight into the coexistence of both laminated and clotted mat structures in close proximity to one another. Here we examine this possibility by comparing eukaryotic diversity based on Sanger and high-throughput pyrosequencing of small subunit ribosomal RNA (18S rRNA) genes. Analyses were based on total RNA extracts as template to minimize input from inactive or deceased organisms. Results identified diverse eukaryotic communities particularly stramenopiles, Alveolata, Metazoa, Amoebozoa, and Rhizaria within different mat types at both locations, as well as abundant and diverse signatures of eukaryotes with <80% sequence similarity to sequences in GenBank. This suggests presence of significant novel eukaryotic diversity, particularly in hypersaline Hamelin Pool. There was evidence of vertical structuring of protist populations and foraminiferal diversity was highest in bioturbated/clotted thrombolite mats of Highborne Cay.This work was funded by grant OCE-0926421 to JMB and VPE and OCE-0926372 to RES

External controls on the distribution, fabrics and mineralization of modern microbial mats in a coastal hypersaline lagoon, Cayo Coco (Cuba).

45 pagesInternational audienceActive, carbonate-mineralizing microbial mats flourish in a tropical, highly evaporative, marine-fed lagoonal network to the south of Cayo Coco Island (Cuba). Hypersaline conditions support the development of a complex sedimentary microbial ecosystem with diverse morphologies, a variable intensity of mineralization and a potential for preservation. In this study, the role of intrinsic (i.e. microbial) and extrinsic (i.e. physicochemical) controls on microbial mat development, mineralization and preservation was investigated. The network consists of lagoons, forming in the interdune depressions of a Pleistocene aeolian substratum; they developed due to a progressive increase in sea-level since the Holocene. The hydrological budget in the Cayo Coco lagoonal network changes from west to east, increasing the salinity. This change progressively excludes grazers and increases the saturation index of carbonate minerals, favouring the development and mineralization of microbial mats in the easternmost lagoons. Detailed mapping of the easternmost lagoon shows four zones with different flooding regimes. The microbial activity in the mats was recorded using light–dark shifts in conjunction with microelectrode O2 and HS− profiles. High rates of O2 production and consumption, in addition to substantial amounts of exopolymeric substances, are indicative of a potentially strong intrinsic control on mineralization. Seasonal, climate-driven water fluctuations are key for mat development, mineralization, morphology and distribution. Microbial mats show no mineralization in the permanently submersed zone, and moderate mineralization in zones with alternating immersion and exposure. It is suggested that mineralization is also driven by water-level fluctuations and evaporation. Mineralized mats are laminated and consist of alternating trapping and binding of grains and microbially induced magnesium calcite and dolomite precipitation. The macrofabrics of the mats evolve from early colonizing Flat mats to complex Cerebroid or Terrace structures. The macrofabrics are influenced by the hydrodynamic regime: wind-driven waves inducing relief terraces in windward areas and flat morphologies on the leeward side of the lagoon. Other external drivers include: (i) storm events that either promote (for example, by bioclasts covering) or prevent (for example, by causing erosion) microbial mat preservation; and (ii) subsurface degassing, through mangrove roots and desiccation cracks covered by Flat mats (i.e. forming Hemispheroids and Cerebroidal structures). These findings provide in-depth insights into understanding fossil microbialite morphologies that formed in lagoonal settings

Prokaryotic diversity in ecosystems associated to minerals from the hypersaline lake Tebenquiche in the Atacama desert

The Salar de Atacama is located in the Chilean central Andes and it is a huge evaporitic system with a large number of saline water bodies in its interior. Lake Tebenquiche is one of the largest and prokaryotic microorganisms inhabiting this lake are subjected to severe conditions as high solar radiation due to a lower barometric pressure at high altitude, extreme daily temperature fluctuations, intense changes in salinity caused by net evaporation and high arsenic concentrations in the water due to volcanic events. Therefore, we decided to analyse the prokaryotic diversity of microbial mats, microbialites and one evaporite by pyrosequencing of the V4 hypervariable region of the 16S rRNA gene. In addition, the total metagenomic DNA of a microbial mat was sequenced to study the genetic and metabolic diversity for understanding the microbial processes associated to minerals in a system at high altitude. Methods: Five different samples were collected from lake Tebenquiche: two microbial mats, TebMa1 and TebMa2; two microbialites, TebMi1 and TebMi2; and one evaporite, TebEv1. The total metagenomic DNA of each sample was extracted and pyrosequenced the V4 hypervariable region of the prokaryotic 16S rRNA gene. The prokaryotic 16S rRNA amplicons were analysed using the QIIME software package. The total metagenomic DNA from microbial mat, TebMa1, was sequenced using paired-end Hi-Seq 1500 Illumina Technology and the raw reads obtained were filtered, assembled into contigs and annotated. Results: Euryarchaeota is one of the most abundant phyla in all samples studied, especially in TebEv1 with 97 % of 16S rRNA sequences. Most of the euryarchaeal OTUs are classified within the class Halobacteria or anaerobic and methanogenic archaea. Specific genes as indicators of particular biogeochemical cycles were searched in the assembled contigs of TebMa1. Nitrogenase gene sequences are found in a high amount and these sequences were aligned with a range of 70%-89% identity to known nitrogenase sequences. Phosphate is mainly obtained by two mechanisms when there is a reduced availability of phosphorous: polyphosphate metabolism and phosphate recycling. Cytoplasmic arsenate reduction and arsenite oxidation are clearly present in the arsenic-rich habitat TebMa1. Conclusions: The high conductivity measured in TebMa2 and TebEv1 must be promoting the growth of members belonging to the class Halobacteria due to the dominance of this taxon in both samples. In TebMa1, we suggest could be carried out an active biological nitrogen fixation by bacteria and archaea and due to the low percentage identity to the closest relative an important part could be novel diazotrophic microorganisms. This ecosystem is rich in arsenic and its inhabitants use arsenic resistance strategies as cytoplasmic arsenate reduction and arsenite oxidation but a possible mechanism employed by these microorganisms could be through quelation of this metalloid using polyphosphates.Fil: Fernandez, Ana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: Rasuk, Maria Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: Contreras, Manuel. Centro de Ecologia Aplicada; ChileFil: Novoa, Fernando. Centro de Ecologia Aplicada; ChileFil: Poire, Daniel Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Visscher, Pieter T.. University of Connecticut; Estados UnidosFil: Ventosa, Antonio. Universidad de Sevilla; EspañaFil: Farias, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaXI Congreso Argentino de Microbiologia GeneralCórdobaArgentinaSociedad Argentina de Microbiología Genera