Maria Dittrich

Aerobic microbial dolomite at the nanometer scale: Implications for the geologic record

Microbial experiments are the only proven approach to produce experimental dolomite under Earths surface conditions. Although microbial metabolisms are known to induce dolomite precipitation by favoring dolomite growth kinetics, the involvement of microbes in the dolomite nucleation process is poorly understood. In particular, the nucleation of microbially mediated dolomite remains a matter for investigation because the metabolic diversity involved in this process has not been fully explored. Herein we demonstrate that Halomonas meridiana and Virgibacillus marismortui, two moderately halophilic aerobic bacteria, mediate primary precipitation of dolomite at low temperatures (25, 35 °C). This report emphasizes the biomineralogical implications for dolomite formation at the nanometer scale. We describe nucleation of dolomite on nanoglobules in intimate association with the bacterial cell surface. A combination of both laboratory culture experiments and natural samples reveals that these nanoglobule structures may be: (1) the initial step for dolomite nucleation, (2) preserved in the geologic record, and (3) used as microbial tracers through time and/or as a proxy for ancient microbial dolomite, as well as other carbonate minerals.

ARE PICOPLANKTON RESPONSIBLE FOR CALCITE PRECIPITATION IN LAKES

Abstract Deposits of lacustrine calcite are important records of environmental changes. In order to interpret these archives, knowledge about the origin of the calcite is essential. It has been accepted that calcite precipitation can be induced by bacteria and algae. However, the detailed mechanisms are still unclear. This review summarizes what is known about the interactions between calcite precipitation and the autotrophic picoplankton. We consider findings from both field and laboratory studies. Field studies show that calcite precipitation in oligotrophic lakes is strongly linked with picocyanobacteria blooms. Laboratory experiments led to the formulation of the mechanism of precipitation induced by microalga. Experiments also showed that precipitation induced by picocyanobacteria is influenced by various factors including the uptake of inorganic carbon and the structure of the cell walls. Recent studies indicate that the influence of environmental conditions like the composition of lake water has to be taken into account as well. We conclude that in situ observations of precipitation processes at picoplankton cells under controlled conditions are needed to improve our understanding of mineral bacteria interaction.

The Role of Autotrophic Picocyanobacteria in Calcite Precipitation in an Oligotrophic Lake

A 1-year field study monitoring depth profiles of picoplankton and physicochemical data in the oligotrophic Lake Lucerne (Switzerland) showed that picocyanobacteria play an important role in the CaCO3 precipitation process. Laboratory experiments with Mychonastes and Chlorella, isolated from Lake Lucerne and Synechococcus using ion selective electrodes, scanning electron microscopy and X-ray powder diffraction clearly demonstrated the potential of picoplankton for fast and effective CaCO3 precipitation. The combination of a field study with laboratory experiments confirmed the previous reports of picocyanobacteria triggering the CaCO3 precipitation in hardwater oligotrophic lakes. Electron micrographs of particles from the water column often reveal the size and shape of picoplankton cells covered by calcite. In addition the results from the laboratory approach indicated that algae and bacteria induced different precipitation mechanisms. Experiments with Mychonastes and Chlorella produced crystalline calcite completely covering the cells. Experiments with the cyanobacteria Synechococcus, however, yielded amorphous, micritic CaCO3, indicating a different precipitation process.

CaCO3 nucleation by cyanobacteria: laboratory evidence for a passive, surface-induced mechanism.

Calcite nucleation on the surface of cyanobacteria of the Synechococcus leopoliensis strain PCC 7942 was investigated to assess the influence of photosynthetic uptake of inorganic carbon and active ion exchange processes across the cell membrane on the nucleation and precipitation mechanisms. We performed long-term precipitation experiments at a constant CO(2) level in ambient air by adding suspensions of previously washed cyanobacteria to solutions of NaHCO(3)/CaCl(2) which were supersaturated with respect to calcite. Induction times between 4 and 110 h were measured over a range of saturation states, Omega, between 8 and 4. The kinetics of CaCO(3) nucleation was compared between experiments: (i) with ongoing photosynthesis, (ii) with cells metabolizing but not undergoing photosynthetic uptake of inorganic carbon and (iii) in darkness without photosynthesis. No significant differences were observed between the three treatments. The results reveal that under low nutrient concentrations and permanent CO(2) supply, photosynthetic uptake of inorganic carbon predominantly uses CO(2) and consequently does not directly influence the nucleation process of CaCO(3) at the surface of S. leopoliensis. Furthermore, ion exchange processes did not affect the kinetics, indicating a passive nucleation process wherein the cell surface or extracellular polymers provided preferential sites for mineral nucleation. The catalyzing effect of the cyanobacteria on calcite nucleation was equivalent to a approximately 18% reduction in the specific interfacial free energy of the calcite nuclei. This result and the ubiquitous abundance of cyanobacteria suggest that this process may have an impact on local and global carbon cycling.

TEM-specimen preparation of cell/mineral interfaces by Focused Ion Beam milling

Abstract Picocyanobacteria were found to play an important role in calcite precipitation in oligotrophic lakes. In this study, investigations on the interface between cyanobacteria and attached biogenic calcite crystals have been performed to gain further insights into the mechanisms of nucleation of these precipitates. Ultramicrotomy, the conventional preparation technique of thin sections for Transmission Electron Microscopy (TEM) investigations, often fails when working on heterogeneous samples containing soft organic material and hard minerals. Thus, in this study the thin sections were prepared using Focused Ion Beam (FIB) milling. This approach is usually applied in material sciences but until recently was not very common in environmental research. Different analytical TEM methods like Electron Spectroscopic Imaging (ESI) and Electron Energy Loss Spectrometry (EELS) were used to test the suitability of FIB-milling for the preparation of organic/inorganic interface specimens. With this approach we were able to analyze both organic and the inorganic phases of the same sample. Elemental maps of the samples were also calculated. By analyzing the structure of the C K-absorption edge, the different bonding forms of the organic carbon cell and the inorganic carbon of the crystal could be clearly distinguished

Carbonate Precipitation through Microbial Activities in Natural Environment, and Their Potential in Biotechnology: A Review.

Calcium carbonate represents a large portion of carbon reservoir and is used commercially for a variety of applications. Microbial carbonate precipitation, a by-product of microbial activities, plays an important metal coprecipitation and cementation role in natural systems. This natural process occurring in various geological settings can be mimicked and used for a number of biotechnologies, such as metal remediation, carbon sequestration, enhanced oil recovery, and construction restoration. In this study, different metabolic activities leading to calcium carbonate precipitation, their native environment, and potential applications and challenges are reviewed.

Interactions between calcite precipitation (natural and artificial) and phosphorus cycle in the hardwater lake

The influence of calcite precipitation on the phosphorus cycle in stratified hardwater lake was studied before and during experiments with a new restoration technique. Surveys of the chemical composition of water column and monitoring of settling particles of Lake Luzin (North–East) showed that calcite precipitation occurs each year over 2–3 periods during spring and summer. The change of the phosphorus content influenced the calcite precipitation intensity. The sedimentation fluxes of phorphorus and the calcite precipitation were closely associated. Based on the hypothesis that calcite precipitation acts as an improvement to the trophic state by enhancing the internal phosphorus sink, this new technology for lake restoration was developed. The hypolimnetic Ca(OH)2 addition during summer stratification in 1996–1997 induced the calcite precipitation in the deep water layer of Basin Carwitz of Lake Schmaler Luzin. The treatment also supported the natural calcite precipitation in the epilimnion. The annual total phosphorus content decreased from 0.46 tons in 1995 to 0.35 tons in 1997. The annual SRP content decreased from 0.02 tons in 1996 to 0.01 tons in 1997 after beginning the artificial calcite precipitation in 1996. The decrease of the annual Chl-a concentration in 1998 on 38% compared with that in 1996 pointed out the lake recovering. According to the one box model, the artificial calcite precipitation affected the P cycle in the lake by suppressing the P release from the sediments.

Atomic force microscope (AFM) combined with the ultramicrotome: a novel device for the serial section tomography and AFM/TEM complementary structural analysis of biological and polymer samples

A new device (NTEGRA Tomo) that is based on the integration of the scanning probe microscope (SPM) (NT‐MDT NTEGRA SPM) and the Ultramicrotome (Leica UC6NT) is presented. This integration enables the direct monitoring of a block face surface immediately following each sectioning cycle of ultramicrotome sectioning procedure. Consequently, this device can be applied for a serial section tomography of the wide range of biological and polymer materials. The automation of the sectioning/scanning cycle allows one to acquire up to 10 consecutive sectioned layer images per hour. It also permits to build a 3‐D nanotomography image reconstructed from several tens of layer images within one measurement session. The thickness of the layers can be varied from 20 to 2000 nm, and can be controlled directly by its interference colour in water.

Phosphorus retention in a mesotrophic lake under transient loading conditions: insights from a sediment phosphorus binding form study.

Phosphorus retention in sediments has been estimated for three basins in Lake Simcoe, a mesotrophic lake in Ontario, Canada. Total phosphorous (TP) fractionation was used to examine the concentration of phosphorus (P) binding forms in the sediments of Cooks Bay, Kempenfelt Bay, and the Main Basin. The extended sequential extractions allowed us to differentiate between organic-, inorganic-, carbonate-bounded and redox-sensitive phosphorus. Our results showed different mechanisms of P release in each of the three investigated basins, which may be linked to their distinct loading histories, present land-uses and morphology of the sampling sites. In the deep Main Basin, where moderate changes in P loading have been induced by deforestation, sediments are not an important long-term source of diagenetically mobile P, as almost 75% of P is released within a short time scale. P release is predominantly generated by a continuous epilimnetic P flux, rather than a large inventory of temporary P stored in the sediments. Diagenesis in the upper sediment layers is fast enough to prevent a large accumulation of temporary P. In the much deeper glacially formed Kempenfelt Bay with a highly urbanized catchment, P release from the sediments is dominated by the redox-sensitive P fraction, representing up to 40% and 57% of long- and short-term sediment P release, respectively. In the shallow and agriculturally-impacted Cooks Bay, the main P binding form that can be mobilized through diagenesis is carbonate-bound P. This fraction contributes 40.1% and 37.6% to the long- and short-term P sediment release, respectively. Although different mechanisms of P release have been revealed for the three basins in Lake Simcoe, the vertical profiles indicate that the sediments throughout the system are still able to bind deposited P.

Lake restoration by hypolimnetic Ca(OH)2 treatment: impact on phosphorus sedimentation and release from sediment.

A whole-lake hypolimnetic Ca(OH)(2) addition, that induced calcium carbonate precipitation, combined with deep water aeration has been applied to eutrophic Lake Luzin, Germany during 1996-1998. In this study we investigated the dynamic of phosphorus and its binding forms in seston and sediment before and during the treatment. The sedimentation rates of phosphorus increased within three years of induced calcite precipitation. The phosphorus binding forms shifted to the calcite-bound phosphorus in the settling matter. The increase of calcite-bound P in the settling material did not coincide with the maximum induced CaCO(3)-precipitation caused by the hypolimnetic addition of Ca(OH)(2). An impact of chemicals additions and pH on phosphorus binding forms in seston and surface sediments has been studied in laboratory experiments with sediment core incubations and slurry experiments. Laboratory studies showed that the lowest phosphorus flux from sediment was related to the experiment with pH=7 in overlaying water adjusted with Ca(OH)(2). The adjusting of pH with Ca(OH)(2) leads to a lower P flux of 2.3 mg Pm(-2)d(-1), while the highest P-flux is attributed to the experiment with the pH which was adjusted with NaOH. Phosphorus fraction which reflects phosphorus binding on carbonates in surface sediments increased within one year of treatment, enhancing the phosphorus retention capacity of sediments.