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