Concepcion Jimenez-Lopez

Precipitation kinetics and carbon isotope partitioning of inorganic siderite at 25°C and 1 atm

Siderite was precipitated from NaHCO3 and Fe(ClO4)2 solutions under anaerobic conditions at 25°C and 1 atm total pressure using a modified version of the chemo-stat technique and the free-drift technique. Samples of solution and solid were withdrawn at different time intervals during time course experiments to determine the bulk and isotope composition of the solution and solid, and the morphology and mineralogy of the solid. A series of metastable precursors precipitated and dissolved sequentially, culminating in well-crystallized siderite rhombohedra having an average edge of ∼ 2 μm and a limited size distribution. Siderite precipitation rate ranged from 100.23 to 102.44 μmol•m−2•h−1 for saturation states (with respect to siderite) ranging from near equilibrium to 103.53. Calculated carbon isotope fractionation factors (103lnα) averaged 8.5 ± 0.2 (1σ n = 4) for the siderite-CO2(g) system and 0.5 ± 0.2 (1σ n = 4) for the siderite-HCO3−(aq) system.

Stone-isolated carbonatogenic bacteria as inoculants in bioconsolidation treatments for historical limestone.

Stone consolidation treatments that use bacterial biomineralization are mainly based on two strategies: (1) the inoculation of a bacterial culture with proven carbonatogenic ability and/or (2) the application of a culture medium capable of activating those bacteria able to induce the formation of calcium carbonate, from amongst the bacterial community of the stone. While the second strategy has been demonstrated to be effective and, unlike first strategy, it does not introduce any exogenous microorganism into the stone, problems may arise when the bacterial community of the stone is altered, for instance by the use of biocides in the cleaning process. In this study we isolate bacteria that belong to the natural microbial community of the stone and which have proven biomineralization capabilities, with the aim of preparing an inoculum that may be used in stone consolidation treatments wherein the natural community of those stones is altered. With this aim, outdoor experiments were undertaken to activate and isolate bacteria that display high biomineralization capacity from altered calcarenite stone. Most of the bacteria precipitated calcium carbonate in the form of calcite. The selected bacteria were phylogenetically affiliated with members of Actinobacteria, Gamma-proteobacteria and Firmicutes. Furthermore, the capability of these selected carbonatogenic bacteria to consolidate altered calcarenite stone slabs was studied in in vitro experiments, both in the presence and the absence of Myxococcus xanthus, as a potential reinforcement for the bacterial biomineralization. Herein, Acinetobacter species, belonging to the microbial community of the stone, are proposed as powerful carbonatogenic bacteria that, inoculated under appropriate conditions, may be used as inoculum for calcareous stone conservation/consolidation in restoration interventions where the microbial community of the stone is altered.

Magnetosomes and magnetite crystals produced by magnetotactic bacteria as resolved by atomic force microscopy and transmission electron microscopy.

Atomic force microscopy (AFM) was used in concert with transmission electron microscopy (TEM) to image magnetotactic bacteria (Magnetospirillum gryphiswaldense MSR-1 and Magnetospirillum magneticum AMB-1), magnetosomes, and purified Mms6 proteins. Mms6 is a protein that is associated with magnetosomes in M. magneticum AMB-1 and is believed to control the synthesis of magnetite (Fe(3)O(4)) within the magnetosome. We demonstrated how AFM can be used to capture high-resolution images of live bacteria and achieved nanometer resolution when imaging Mms6 protein molecules on magnetite. We used AFM to acquire simultaneous topography and amplitude images of cells that were combined to provide a three-dimensional reconstructed image of M. gryphiswaldense MSR-1. TEM was used in combination with AFM to image M. gryphiswaldense MSR-1 and magnetite-containing magnetosomes that were isolated from the bacteria. AFM provided information, such as size, location and morphology, which was complementary to the TEM images.

Subcellular localization of the magnetosome protein MamC in the marine magnetotactic bacterium Magnetococcus marinus strain MC-1 using immunoelectron microscopy.

Magnetotactic bacteria are a diverse group of prokaryotes that biomineralize intracellular magnetosomes, composed of magnetic (Fe3O4) crystals each enveloped by a lipid bilayer membrane that contains proteins not found in other parts of the cell. Although partial roles of some of these magnetosome proteins have been determined, the roles of most have not been completely elucidated, particularly in how they regulate the biomineralization process. While studies on the localization of these proteins have been focused solely on Magnetospirillum species, the goal of the present study was to determine, for the first time, the localization of the most abundant putative magnetosome membrane protein, MamC, in Magnetococcus marinus strain MC-1. MamC was expressed in Escherichia coli and purified. Monoclonal antibodies were produced against MamC and immunogold labeling TEM was used to localize MamC in thin sections of cells of M. marinus. Results show that MamC is located only in the magnetosome membrane of Mc. marinus. Based on our findings and the abundance of this protein, it seems likely that it is important in magnetosome biomineralization and might be used in controlling the characteristics of synthetic nanomagnetite.

Structure-function studies of the magnetite-biomineralizing magnetosome-associated protein MamC.

Magnetotactic bacteria are Gram-negative bacteria that navigate along geomagnetic fields using the magnetosome, an organelle that consists of a membrane-enveloped magnetic nanoparticle. Magnetite formation and its properties are controlled by a specific set of proteins. MamC is a small magnetosome-membrane protein that is known to be active in iron biomineralization but its mechanism has yet to be clarified. Here, we studied the relationship between the MamC magnetite-interaction loop (MIL) structure and its magnetite interaction using an inert biomineralization protein-MamC chimera. Our determined structure shows an alpha-helical fold for MamC-MIL with highly charged surfaces. Additionally, the MamC-MIL induces the formation of larger magnetite crystals compared to protein-free and inert biomineralization protein control experiments. We suggest that the connection between the MamC-MIL structure and the proteins charged surfaces is crucial for magnetite binding and thus for the size control of the magnetite nanoparticles.

Myxococcus xanthus Colony Calcification: An Study to Better Understand the Processes Involved in the Formation of this Stromatolite-Like Structure

Calcium carbonate precipitation is a common phenomenon in nature and has been observed to be mediated by a number of microorganisms (for a review, see Castanier et al. 2000; Wright and Oren 2005). Bacterially induced carbonate mineralization is important in a wide range of processes including atmospheric CO2 budgeting (Braissant et al. 2002; Ehrlich 2002), carbonate sediment and rock formation (Riding 2000; Ben Chekroun et al.

Chemical Purity of Shewanella oneidensis-Induced Magnetites

Magnetite is a common iron oxide produced both inorganically and biogenically. Biologically-induced magnetite is often originated, under appropriate conditions, as a result of the Fe3+ reduction by dissimilatory iron reducing bacteria, which are usually found in anoxic environments or at the oxic-anoxic interface. Such a Fe3+ bioreduction occurs upon this cation acting as an electron acceptor of an anaerobic respiration, thus creating favorable conditions for magnetite precipitation. This biologically-induced magnetite is an important biomineral in the environments inhabited by iron reducing bacteria. The presence of a variety of cations may influence both the biomineralization process and the resulting biomineral, however this phenomenon has not been investigated extensively. In the present study, we study the effect on the magnetite biomineralization process of the presence of calcium, magnesium and manganese in the culture medium where Shewanella oneidensis lives. We also test the incorporation of these cations into the crystalline structure of inorganic and biogenic magnetite induced by S. oneidensis. According to our findings, manganese ions likely become incorporated into the crystal structure of biologically produced magnetites, while magnesium ions are incorporated in inorganic magnetites, and calcium ions are excluded from the crystal structure of both inorganic and biotic magnetites. We hypothesize that the incorporation of cations into magnetite depends not only on the relative cation radii, but also on the mechanisms of magnetite formation.

THE INFLUENCE OF HYDROSTATIC PRESSURE ON SHELL MINERALIZATION OF ANODONTA CYGNEA: A COMPARATIVE STUDY WITH A HYDROTHERMAL VENT BIVALVE BATHYMODIOLUS AZORICUS

ABSTRACT The objective of this study was to determine at what level the shell mineralization of Anodonta cygnea, a shallow freshwater bivalve, is influenced by external physical—chemical factors, mainly concerning the habit and microstructure of the calcium carbonate crystals. A detailed examination of the inner shell layers of A. cygnea was carried out by scanning electron microscopy in animals living under natural environment conditions and after being exposed to artificially high hydrostatic pressure. Groups of 6 animals were exposed to different hydrostatic pressure (10, 20, 40, or 80 bar) in a hyperbaric chamber for 10 days. In general, we noted that the high pressure induced strong changes in the microstructure of all regions of the shell inner layer in A. cygnea, probably by altering organic matrix deposition, under every hyperbaric value. In fact, observations of the prismatic layer showed some significant alterations, presenting fibrous spherulitic crystalline arrangements instead of the nondenticular composite crystals. At the beginning of the nacreous layer, experimental animals showed several (5–7) superimposed lamellae consisting of unconnected round tablets. In the following regions, the nacreous layer with hexagonal-rhombohedral crystals displayed an intense growth resembling columnar formations resulting from a greater number of mineral layers, many more than would be expected. A similar phenomenon was also revealed in the inner palliai line regions of the exposed A. cygnea bivalves, with simultaneous visualization of more than 10–15 layers of nacre in contrast with 3–4 seen in natural situations. Curiously, similarly altered microstructures were observed in shell calcareous layers of a hydrothermal vent deepsea bivalve Bathymodiolus azoricus, particularly in the nacreous layer. This natural occurrence, together with the experimental work on A. cygnea, might imply that hydrostatic pressure is a physical parameter of great importance in microstructure definition. The basic mechanism is probably related to deficient chitin (or similar) polymerization, which promotes the vertical growth of the nacre crystals.

Learning from magnetotactic bacteria: A review on the synthesis of biomimetic nanoparticles mediated by magnetosome-associated proteins

Much interest has gained the biomineralization process carried out by magnetotactic bacteria. These bacteria are ubiquitous in natural environments and share the ability to passively align along the magnetic field lines and actively swim along them. This ability is due to their magnetosome chain, each magnetosome consisting on a magnetic crystal enveloped by a lipid bilayer membrane to which very unique proteins are associated. Magnetotactic bacteria exquisitely control magnetosome formation, making the magnetosomes the ideal magnetic nanoparticle of potential use in many technological applications. The difficulty to scale up magnetosome production has triggered the research on the in vitro production of biomimetic (magnetosome-like) magnetite nanoparticles. In this context, magnetosome proteins are being used to mediate such in vitro magnetite precipitation experiments. The present work reviews the knowledgement on the magnetosome proteins thought to have a role on the in vivo formation of magnetite crystals in the magnetosome, and the recombinant magnetosome proteins used in vitro to form biomimetic magnetite. It also summarizes the data provided in the literature on the biomimetic magnetite nanoparticles obtained from those in vitro experiments.

Nanocrystalline structures in calcium carbonate biominerals

Biological carbonate mineralization induced by both microorganisms and higher phyla organisms is very important in many different natural processes. The organisms precipitate calcium carbonate to form very sophisticated biomaterials that they used for many different functions. Organisms control calcium carbonate precipitation using specific organic macromolecules which are released at specific times and regulate crystal growth. Calcium carbonate crystals are formed and arranged in several representative biomaterials (e.g., avian eggshell, mollusk nacre and bacterially induced precipitates). Through these examples, we get an insight on how organisms are not only able to precipitate calcium carbonate but also comprehensively on how organisms control this process, during the nucleation, polymorphism selection and crystal growth stages, resulting in materials which highly reproducible characteristics at different scales from the nano- to the millimeter scale. The ordered arrangement of crystals in these materials is in part controlled by the organic matrix and in part determined by self-organization processes.