Quantcast


CURATOR
A pinboard by
Óscar Cabestrero

PhD candidate, Complutense University of Madrid

PINBOARD SUMMARY

Microbial mat manipulations & experiments to understand biominerals precipitation in ephemeral lakes

Understanding microbial carbonate precipitation from a highly alkaline lake using laboratory manipulated mats and experiments: The processes of carbonate precipitation may be observed in modern playa-lakes, where carbonates, sulfates and chlorides are associated with microbial mats (Sanz-Montero et al., 2013; Cabestrero et al., 2015). Modern and natural evaporitic microbial environments are important analogs for understanding brine evolution and mineral precipitation pathways in shallow water settings that have existed since the Archean on Earth and perhaps on Mars. Microbialites comprised of up to 45% hydromagnesite, 25% of calcite and 20% of dolomite have been recognized by microscopy and XRD in Eras playa-lake, Central Spain (Cabestrero and Sanz-Montero, 2016). Calcite, dolomite and hydromagnesite are commonly supersaturated in the analyzed waters although experiments replicating lake physicochemistry (using filtered natural water samples) showed that they do not precipitate directly from the brine. Many authors also confirmed the difficulties to precipitate Mg/Ca carbonates inorganically. Sulphates, chlorides, Na-carbonates and nesquehonite are supposed to precipitate directly from the brine as it evaporates but they are always undersaturated in the Lake water samples. Thus, these minerals should have precipitated favored by microbial mats EPS ion exchange in microenvironments. Micro niches cannot be directly assessed by common techniques (microscopy and XRD), so, in order to understand mineral formation forced precipitation experiments were designed. References: Cabestrero Ó, Sanz-Montero ME. 2016. Brine evolution in two inland evaporative environments: influence of microbial mats in mineral precipitation. Journal of Paleolimnology. 1-19. Cabestrero Ó, Arregui L, Sanz-Montero E, Serrano S. 2015. Biodiversity of protists and prokaryotes of two playa-lakes from Central Spain. Abstract book: VII European Congress of Protistology, Seville, Spain. Sanz-Montero ME, Arroyo X, Cabestrero Ó, Calvo JP, Fernández-Escalante E, Fidalgo C, García-del-Cura MA, García-Avilés J, González-Martín JA, Rodríguez-Aranda JP, Rovira JV. 2013. Procesos de sedimentación y biomineralización en la laguna alcalina de las Eras (Humedal Coca-Olmedo). Geogaceta. 53: 97-100

8 ITEMS PINNED

Dynamics of archaea at fine spatial scales in Shark Bay mat microbiomes.

Abstract: The role of archaea in microbial mats is poorly understood. Delineating the spatial distribution of archaea with mat depth will enable resolution of putative niches in these systems. In the present study, high throughput amplicon sequencing was undertaken in conjunction with analysis of key biogeochemical properties of two mats (smooth and pustular) from Shark Bay, Australia. One-way analysis of similarity tests indicated the archaeal community structures of smooth and pustular mats were significantly different (global R = 1, p = 0.1%). Smooth mats possessed higher archaeal diversity, dominated by Parvarchaeota. The methanogenic community in smooth mats was dominated by hydrogenotrophic Methanomicrobiales, as well as methylotrophic Methanosarcinales, Methanococcales, Methanobacteriales and Methanomassiliicoccaceae. Pustular mats were enriched with Halobacteria and Parvarchaeota. Key metabolisms (bacterial and archaeal) were measured, and the rates of oxygen production/consumption and sulfate reduction were up to four times higher in smooth than in pustular mats. Methane production peaked in the oxic layers and was up to seven-fold higher in smooth than pustular mats. The finding of an abundance of anaerobic methanogens enriched at the surface where oxygen levels were highest, coupled with peak methane production in the oxic zone, suggests putative surface anoxic niches in these microbial mats.

Pub.: 12 Apr '17, Pinned: 15 Jun '17

A Study of the Microbial Spatial Heterogeneity of Bahamian Thrombolites Using Molecular, Biochemical, and Stable Isotope Analyses.

Abstract: Thrombolites are buildups of carbonate that exhibit a clotted internal structure formed through the interactions of microbial mats and their environment. Despite recent advances, we are only beginning to understand the microbial and molecular processes associated with their formation. In this study, a spatial profile of the microbial and metabolic diversity of thrombolite-forming mats of Highborne Cay, The Bahamas, was generated by using 16S rRNA gene sequencing and predictive metagenomic analyses. These molecular-based approaches were complemented with microelectrode profiling and in situ stable isotope analysis to examine the dominant taxa and metabolic activities within the thrombolite-forming communities. Analyses revealed three distinctive zones within the thrombolite-forming mats that exhibited stratified populations of bacteria and archaea. Predictive metagenomics also revealed vertical profiles of metabolic capabilities, such as photosynthesis and carboxylic and fatty acid synthesis within the mats that had not been previously observed. The carbonate precipitates within the thrombolite-forming mats exhibited isotopic geochemical signatures suggesting that the precipitation within the Bahamian thrombolites is photosynthetically induced. Together, this study provides the first look at the spatial organization of the microbial populations within Bahamian thrombolites and enables the distribution of microbes to be correlated with their activities within modern thrombolite systems. Key Words: Thrombolites-Microbial diversity-Metagenome-Stable isotopes-Microbialites. Astrobiology 17, 413-430.

Pub.: 19 May '17, Pinned: 15 Jun '17

Unveiling microbial interactions in stratified mat communities from a warm saline shallow pond.

Abstract: Modern phototrophic microbial mats are complex communities often used as analogs of major Precambrian ecosystems. Characterizing biotic, notably metabolic, interactions among different microbial mat members is essential to gain insights into the ecology and biogeochemistry of these systems. We applied 16S/18S rRNA metabarcoding approaches to characterize the structure of archaea, bacteria and protist communities from microbial mats collected along strong physicochemical (oxygen, salinity, temperature, depth) gradients in a shallow pond at the salar de Llamara (Chile). All mats were highly diverse, including members of virtually all known high-rank eukaryotic and prokaryotic taxa but also many novel lineages. Bacterial candidate divisions accounted for almost 50% of sequences in deeper mats, while Archaea represented up to 40% of sequences in some mat layers. Molecular phylogenetic analyses revealed six novel deeply divergent archaeal groups, along abundant and diverse Pacearchaeota and Woesearchaeota. Multivariate statistical analyses showed that local environmental conditions strongly influenced community composition. Co-occurrence network structure was markedly different between surface mats located in the oxygenated zone and mats located in transition and anoxic water layers. We identified potential biotic interactions between various high- and low-rank taxa. Notably, a strong positive correlation was observed between Lokiarchaeota and the poorly known candidate bacterial division TA06.

Pub.: 11 May '17, Pinned: 15 Jun '17

Inside the alkalinity engine: the role of electron donors in the organomineralization potential of sulfate-reducing bacteria.

Abstract: Mineral precipitation in microbial mats may have been the key to their preservation as fossil stromatolites, potentially documenting evidence of the earliest life on Earth. Two factors that contribute to carbonate mineral precipitation are the saturation index (SI) and the presence of nucleation sites. Both of these can be influenced by micro-organisms, which can either alter SI through their metabolisms, or produce and consume organic substances such as extracellular polymeric substances (EPS) that can affect nucleation. It is the balance of individual metabolisms within the mat community that determines the pH and the dissolved inorganic carbon concentration, thereby potentially increasing the alkalinity and consequently the SI. Sulfate-reducing bacteria (SRB) are an important component of this 'alkalinity engine.' The activity of SRB often peaks in layers where CaCO(3) precipitates, and mineral precipitation has been demonstrated in SRB cultures; however, the effect of their metabolism on the alkalinity engine and actual contribution to mineral precipitation is the subject of controversy. Here, we show through culture experiments, theoretical calculations, and geochemical modeling studies that the pH, alkalinity, and organomineralization potential will vary depending on the type of electron donor. Specifically, hydrogen and formate can increase the pH, but electron donors like lactate and ethanol, and to a lesser extent glycolate, decrease the pH. The implication of this for the lithification of mats is that the combination of processes supplying electron donors and the utilization of these compounds by SRB may be critical to promoting mineral precipitation.

Pub.: 29 Aug '12, Pinned: 08 Jun '17

Characterization of bacterial diversity associated with microbial mats, gypsum evaporites and carbonate microbialites in thalassic wetlands: Tebenquiche and La Brava, Salar de Atacama, Chile.

Abstract: In this paper, we report the presence of sedimentary microbial ecosystems in wetlands of the Salar de Atacama. These laminated systems, which bind, trap and precipitate mineral include: microbial mats at Laguna Tebenquiche and Laguna La Brava, gypsum domes at Tebenquiche and carbonate microbialites at La Brava. Microbial diversity and key biogeochemical characteristics of both lakes (La Brava and Tebenquiche) and their various microbial ecosystems (non-lithifying mats, flat and domal microbialites) were determined. The composition and abundance of minerals ranged from trapped and bound halite in organic-rich non-lithifying mats to aragonite-dominated lithified flat microbialites and gypsum in lithified domal structures. Pyrosequencing of the V4 region of the 16s rDNA gene showed that Proteobacteria comprised a major phylum in all of the microbial ecosystems studied, with a marked lower abundance in the non-lithifying mats. A higher proportion of Bacteroidetes was present in Tebenquiche sediments compared to La Brava samples. The concentration of pigments, particularly that of Chlorophyll a, was higher in the Tebenquiche than in La Brava. Pigments typically associated with anoxygenic phototrophic bacteria were present in lower amounts. Organic-rich, non-lithifying microbial mats frequently formed snake-like, bulbous structures due to gas accumulation underneath the mat. We hypothesize that the lithified microbialites might have developed from these snake-like microbial mats following mineral precipitation in the surface layer, producing domes with endoevaporitic communities in Tebenquiche and carbonate platforms in La Brava. Whereas the potential role of microbes in carbonate platforms is well established, the contribution of endoevaporitic microbes to formation of gypsum domes needs further investigation.

Pub.: 21 Jan '14, Pinned: 08 Jun '17

Brine evolution in two inland evaporative environments: influence of microbial mats in mineral precipitation

Abstract: This paper gives new insight into the precipitation sequences in six playa basins that host microbial mats. The study basins are distributed across two evaporitic endorheic drainage systems located in the Central part of Spain with markedly different hydrochemistry and mineralogy. One group, in the north, consists of highly alkaline, brackish to saline lakes containing a high concentration of chloride with dominant carbonate over sulphates. A second group of lakes are mesosaline to hypersaline, with sulphate the dominant anion over chloride. Mineral assemblages identified in both contain several phases that provide evidence for mixed carbonate-sulphate precipitation pathways, in the north, and sulphate-dominated pathways in the south. Regardless of their ionic composition, saline lakes support thin veneers of microbial mats which, by integrating several lines of evidence (hydrochemical and physical analyses, statistical analyses of ions, mineralogical assemblages, textural relationships among mineral phases and microbial mats) are shown to modify the chemical behavior of the evaporitic sediment and promote the formation of carbonates and sulphates from Ca-poor waters with high Mg/Ca ratios. Geochemical changes induced in the environment surrounding the microorganism favor the nucleation of hydrated Mg-carbonates (hydromagnesite and nesquehonite), calcite and dolomite. Simultaneously, the microbial mats provide nucleation sites for gypsum crystals, where they are subjected to episodic stages of growth and dissolution due to saturation indices close to zero. In addition, the bubbles produced by the metabolic activities of microorganisms are shown to promote the precipitation of hydrated Mg-sulphates, despite permanent subsaturation levels. Although common in the studied playa basins, this effect has not been previously reported and is key to understanding sulphate behavior and distribution. Modern and natural evaporitic microbial environments are important analogs for understanding brine evolution and mineral precipitation pathways in shallow water settings that have existed since the Archean on Earth and perhaps on Mars. This paper gives new insight into the precipitation sequences in six playa basins that host microbial mats. The study basins are distributed across two evaporitic endorheic drainage systems located in the Central part of Spain with markedly different hydrochemistry and mineralogy. One group, in the north, consists of highly alkaline, brackish to saline lakes containing a high concentration of chloride with dominant carbonate over sulphates. A second group of lakes are mesosaline to hypersaline, with sulphate the dominant anion over chloride. Mineral assemblages identified in both contain several phases that provide evidence for mixed carbonate-sulphate precipitation pathways, in the north, and sulphate-dominated pathways in the south. Regardless of their ionic composition, saline lakes support thin veneers of microbial mats which, by integrating several lines of evidence (hydrochemical and physical analyses, statistical analyses of ions, mineralogical assemblages, textural relationships among mineral phases and microbial mats) are shown to modify the chemical behavior of the evaporitic sediment and promote the formation of carbonates and sulphates from Ca-poor waters with high Mg/Ca ratios. Geochemical changes induced in the environment surrounding the microorganism favor the nucleation of hydrated Mg-carbonates (hydromagnesite and nesquehonite), calcite and dolomite. Simultaneously, the microbial mats provide nucleation sites for gypsum crystals, where they are subjected to episodic stages of growth and dissolution due to saturation indices close to zero. In addition, the bubbles produced by the metabolic activities of microorganisms are shown to promote the precipitation of hydrated Mg-sulphates, despite permanent subsaturation levels. Although common in the studied playa basins, this effect has not been previously reported and is key to understanding sulphate behavior and distribution. Modern and natural evaporitic microbial environments are important analogs for understanding brine evolution and mineral precipitation pathways in shallow water settings that have existed since the Archean on Earth and perhaps on Mars.

Pub.: 16 Nov '16, Pinned: 08 Jun '17