•V. massiliensis increased pH to 9.1 under the action of NH3 and CA in HW.•Ca2+ ion precipitation ratios reached 87%−98% in immobilized bacterial groups.•Immobilized bacteria decrease the inhibition ...effect of NaCl on Ca2+ ion removal.•Humic acid-like substances, protein, DNA and polysacharide promoted Ca2+ removal.•3 biomineralization pathes were studied besides recycled and precultured bacteria.
Much attention has been paid to Ca2+ ion removal by biomineralization due to the dangers of Ca2+ on industrial processes and human health. However, Ca2+ removal from hypersaline water by biomineralization is quite difficult due to there being few halophilic bacteria tolerating higher salinities. In this study, free and immobilized Virgibacillus massiliensis C halophilic bacteria exhibiting carbonic anhydrase activity were used to remove Ca2+ ions from water at different NaCl concentrations. With increasing NaCl concentrations (10, 50, 100, 150 and 200 g/L), Ca2+ ion concentrations in the presence of free bacteria and in two groups of immobilized bacteria for a period of 6 days sharply decreased from 1200 mg/L to 219–562 mg/L, 71–214 mg/L and 21–159 mg/L, respectively; Ca2+ precipitation ratios were 55%-81%, 82%-94% and 87%-98%, respectively. The humic acid-like substances, protein, DNA and polysaccharide, released by the bacteria, promoted the Ca2+ ion removal. The immobilized bacteria were able to be recycled and precultured, which would save industry costs and increase Ca2+ ion removal efficiency. Biological processes for Ca2+ ion removal include cell surface, intracellular and extracellular biomineralization. The biogenesis of calcium carbonate was proved by SEM-EDS, FTIR, XPS and stable carbon isotope values. This study provides insights into the effective removal of Ca2+ ions by biomineralization in hypersaline water.
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Bacterial activities have been demonstrated as critical for protodolomite precipitation in specific aqueous conditions, whereas the relationship between the various hydrochemical factors and ...bacterial activity has not been fully explored. In this study, biomineralization experiments were conducted using a newly isolated extreme halophilic bacterium from salina mud,
QPL2, under various Mg/Ca molar ratios (0, 3, 6, 10, and 12) and a salinity of 200‰. The mineral phases, elemental composition, morphology, and crystal lattice structure of the precipitates were analyzed by XRD, SEM, and HRTEM, respectively. The organic weight and functional groups in the biominerals were identified by TG-DSC, FTIR, and XPS analysis. The amounts of amino acids and polysaccharides in the EPS of QPL2 cultured at various Mg/Ca molar ratios were quantified by an amino acid analyzer and high-performance liquid chromatography. The results confirm that disordered stoichiometric protodolomite was successfully precipitated through the activities of bacteria in a medium with relatively high Mg/Ca molar ratios (10 and 12) but it was not identified in cultures with lower Mg/Ca molar ratios (0, 3, and 6). That bacterial activity is critical for protodolomite formation as shown by the significant bacterial relicts identified in the precipitated spherulite crystals, including pinhole structures, a mineral coating around cells, and high organic matter content within the crystals. It was also confirmed that the high Mg/Ca molar ratio affects the composition of the organic components in the bacterial EPS, leading to the precipitation of the protodolomite. Specifically, not only the total EPS amount, but also other facilitators including the acidic amino acids (Glu and Asp) and polysaccharides in the EPS, increased significantly under the high Mg/Ca molar ratios. Combined with previous studies, the present findings suggest a clear link between high Mg/Ca molar ratios and the formation of protodolomite through halophilic bacterial activity.
Travertines, which precipitate from high temperature water saturated with calcium carbonate, are generally considered to be dominated by physico-chemical and microbial precipitates. Here, as an ...additional influence on organomineral formation, metagenomic data and microscopic analyses clearly demonstrate that highly diverse viral, bacterial and archaeal communities occur in the biofilms associated with several modern classic travertine sites in Europe and Asia, along with virus-like particles. Metagenomic analysis reveals that bacteriophages (bacterial viruses) containing icosahedral capsids and belonging to the Siphoviridae, Myoviridae and Podoviridae families are the most abundant of all viral strains, although the bacteriophage distribution does vary across the sampling sites. Icosahedral shapes of capsids are also the most frequently observed under the microscope, occurring as non-mineralized through to mineralized viruses and virus-like particles. Viruses are initially mineralized by Ca-Si amorphous precipitates with subordinate Mg and Al contents; these then alter to nanospheroids composed of Ca carbonate with minor silicate 80-300 nm in diameter. Understanding the roles of bacteriophages in modern carbonate-saturated settings and related organomineralization processes is critical for their broader inclusion in the geological record and ecosystem models.
Calcium ions in industrial wastewater needs to be removed to prevent the production of limescale, which can have negative consequences. Biomineralization has become the focus due to its lower costs ...than traditional methods of remediation. In this study, calcium ions were bio-precipitated under the action of free and immobilized Bacillus amyloliquefaciens DMS6 bacteria, and the calcium ion removal efficiency was also compared. The results show that it only needed 3 days to decrease the calcium ion concentration to an ideal level of 76-116 mg/L under the action of DMS6 bacteria immobilized by activated carbon fiber, with calcium ion removal ratios reaching 99%-95% by the 7th day. DMS6 bacteria immobilized by activated carbon fiber were superior to free bacteria and bacteria immobilized by sodium alginate in calcium ion removal. Calcium ions are biomineralized into calcite, Mg-rich calcite, aragonite and monohydrocalcite with abundant organic functional groups, 4 types of secondary protein structures, amino acids, phospholipids, negative stable carbon isotope δ13CPDB values (-16.68‰ to-17.25‰) and negatively charged biomineral surface. Calcium ions were diffused into cells and took part in the intracellular biomineralization of monohydrocalcite, also facilitating calcium ion removal. The formation of intracellular monohydrocalcite has rarely been reported. This study demonstrates an economic and environmentally friendly method to remove calcium ions from industrial wastewater.
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•DMS6 bacteria immobilized by ACF decreased 99-95% of soluable Ca2+ on the 7th day.•DMS6 bacteria immobilized by SA decreased 95%-92% of soluable Ca2+ on the 10th day.•Free DMS6 bacteria decreased 82-81% of soluable Ca2+ on the 17th day.•The formation of intracellular monohydracalcite also facilitated to Ca2+ removal.•The biogenesis of these calcium carbonate minerals was confirmed.
The assembly process of Organic Matter (OM) from single molecules to polymers and the formation process of Ca–CO3 ion-pairs are explored at the micro-scale, and then the relationship between OM and ...carbonate based on the results of microbially-induced carbonate precipitation (MICP) laboratory experiments is established at the macro-scale. Molecular dynamics (MD) is used to model the assembly of OM (a) in an aqueous solution, (b) on surfaces of calcite (10 1‾ 4) crystals and (c) on defective calcite (101‾ 4) crystal surfaces. From the MICP experiments, carbonate minerals containing abundant OM were precipitated and were characterized by Scanning Electron Microscopy (SEM), X-Ray Diffractometry (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The results of the MD show that OM is assembled into polymers in all three simulation systems. Although the Ca–CO3 ion-pairs and OM were briefly combined, the aggregation assembly of OM molecules and the precipitation of carbonate calcium are not related in the long run. The highly specific surface area of the defective calcite shows an increase in the adsorption of OM. The van der Waals forces, which are primarily responsible for controlling the assembly of OM molecules, increase with the degree of aggregation. According to the MICP experiments, OM is enriched on the mineral surfaces, and more OM is found at the steps of defective crystals with their larger surface areas. Through MD and MICP laboratory experiments, this work systematically describes the interaction of OM and carbonate minerals from the micro to the macro scales, and this provides insight into the interaction between OM and carbonates and biogeochemical processes related to the accumulation of OM in sediments.
•The interaction between organic matter and carbonate during sedimentation is examined from the micro to macro scale•The assembly of OM and the formation of Ca–CO3 ion pairs in an aqueous solution are transitory•The adsorption of organic matter is increased by surface defects in the calcite
Ca
2+
, Mg
2+
, and Sr
2+
are elements with similar ionic and hydrochemical characteristics, yet the microbial mineralization behavior in their coexisting environments is seldomly explored. In this ...study, the cyanobacterium Synechocystis sp. PCC6803 was used to induce the precipitation of minerals in mediums with various Mg/Ca and Sr/Ca ratios (Ca
2+
= 0.01 M). The medium hydrochemistry, including cell density, solution pH, and alkalinity, was recorded periodically. The bio-precipitates were characterized with X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), Fourier Translation Infrared spectroscopy (FT-IR), and Thermal Gravimetric Analyzer (TGA). The results show the growth of Synechocystis sp. PCC6803 was inhibited by increasing ionic strength, although the final alkalinity and pH values of the medium were not affected. Two crystalline minerals, calcite (CaCO
3
) and strontianite (SrCO
3
) were precipitated in the mediums with low ionic strength; these were transformed from early amorphous precipitates by a dissolution and re-precipitation mechanism. The morphology of the precipitated cyanobacterial strontianite changed from columnar to dumbbell shape and finally into a spherulite shape. High concentrations of Sr
2+
, like Mg
2+
, prolonged the stabilization of amorphous carbonate precipitates. The acidic amino acids (Glu and Asp) in the EPS of Synechocystis sp. PCC6803 cultured in mediums with high Sr
2+
and high Mg
2+
concentrations increased significantly, compared to those cultured in a medium with no Sr
2+
or Mg
2+
(p < 0.005) ions. The negative binding energy calculated by Density Functional Theory (DFT) on the binding between the two acidic amino acids (Glu and Asp) and ion-H
2
O complexes (CaH
2
O
6
2+
, MgH
2
O
6
2+
, and SrH
2
O
6
2+
), indicating that they are all thermodynamically-favored processes. Consequently, lower energy was needed in their subsequent precipitation and nucleation within the EPS of Synechocystis sp. PCC6803. This inferred process was also supported by the appearance of amorphous particles in the EPS of Synechocystis sp. PCC6803.
Bacteria can facilitate the increase of Mg
2+
content in biotic aragonite, but the molecular mechanisms of the incorporation of Mg
2+
ion into aragonite facilitated by bacteria are still unclear and ...the dolomitization of aragonite grains is rarely reported. In our laboratory experiments, the content of Mg
2+
ions in biotic aragonite is higher than that in inorganically-precipitated aragonite and we hypothesize that the higher Mg content may enhance the subsequent dolomitization of aragonite. In this study, biotic aragonite was induced by
Bacillus licheniformis
Y
1
at different Mg/Ca molar ratios. XRD data show that only aragonite was precipitated in the media with Mg/Ca molar ratios at 6, 9, and 12 after culturing for 25 days. The EDS and atomic absorption results show that the content of Mg
2+
ions in biotic aragonite increased with rising Mg/Ca molar ratios. In addition, our analyses show that the EPS from the bacteria and the organics extracted from the interior of the biotic aragonite contain the same biomolecules, including Ala, Gly, Glu and hexadecanoic acid. The content of Mg
2+
ions in the aragonite precipitates mediated by biomolecules is significantly higher than that in inorganically-precipitated aragonite. Additionally, compared with Ala and Gly, the increase of the Mg
2+
ions content in aragonite promoted by Glu and hexadecanoic acid is more significant. The DFT (density functional theory) calculations reveal that the energy needed for Mg
2+
ion incorporation into aragonite mediated by Glu, hexadecanoic acid, Gly and Ala increased gradually, but was lower than that without acidic biomolecules. The experiments also show that the Mg
2+
ion content in the aragonite significantly increased with the increasing concentration of biomolecules. In a medium with high Mg
2+
concentration and with bacteria, after 2 months, micron-sized dolomite rhombs were precipitated on the surfaces of the aragonite particles. This study may provide new insights into the important role played by biomolecules in the incorporation of the Mg
2+
ions into aragonite. Moreover, these experiments may contribute towards our understanding of the dolomitization of aragonite in the presence of bacteria.
In a multi‐scale approach to the study of the organic and mineral components in an active barrage‐type tufa system of southern Italy, neo‐formed deposits, in both natural depositional sites and on ...inorganic substrates placed in the stream for this study, were observed and compared through one year of monitoring. Dams and lobes representing the basic morpho‐facies of the deposits are composed of two depositional facies: vacuolar tufa (a mixture of phytoclastic and framestone tufa) and stromatolitic tufa (phytoherm boundstone tufa). Three petrographic components comprise both facies: micrite and microsparite, often forming peloidal to aphanitc, laminar and dendrolitic fabrics, and sparite, which occurs as isolated to coalescent fan‐shaped crystals forming botryoids or continuous crusts. All fabrics occurring in all depositional facies are organized into layers with a more or less well‐developed cyclicity, which has its best expression in stromatolitic lamination. The precipitation of all types of calcite (with Mg 1·0 to 3·2 mole % and Sr 0·5 to 0·8 mole %) takes place more or less constantly during all seasons, in spite of the low saturation state of the water (the saturation index range is 0·75 to 0·89) within the active depositional zone; the latter extends for a few hundred microns through the external surface of the deposit. The active depositional zone has a particular micro‐morphology composed of porous micro‐columns (50 to 150 μm in size), separated by interstitial channels. Mineral precipitation occurs upon both external surfaces and within internal cavities of the micro‐columns, while further point sites of precipitation occur suspended within the masses of cyanobacterial tufts. Sub‐spherical mineral units, ‘nano‐spheres’ (10 to 20 nm in diameter) are the basic biotic neo‐precipitate; they commonly form by replacing non‐living degrading organic matter and at point sites along the external surface of living cyanobacterial sheaths. Nano‐spheres agglutinate to form first rod‐shaped aggregates (100 to 200 nm) which then evolve into triads of fibres or polyhedral structures. Successively, both triads and polyhedral solids coalesce to form larger calcite crystals (mainly tetrahedrons tens of microns in size) that represent the fundamental bricks for the construction of the micro‐columns in the active depositional zone. Precipitation is attributed to the presence of a widespread biofilm that occurs in the active depositional zone; this is composed of a heterogeneous community comprising epilithic and endolithic filamentous cyanobacteria, green algae, unicellular prokaryotes, actinobacteria and fungi, with a variable amount of extracellular polymeric substances. No precipitation takes place where the biofilm is absent, indicating that the biological activities of the biofilm are crucial, with its living organisms and non‐living organic matter. Basic aggregates of neo‐precipitates do not form in association with any one particular type of organic matter substrate, but appear to be related to the seasonal temperature variation: polyhedral micro‐crystals mainly precipitate in the colder season, short triads in the intermediate seasons, and long triads in the warmest conditions. These three basic crystal aggregates have a petrographic counterpart, respectively, in the spar, microspar and micrite.
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