Rolf Warthmann

Bio: Rolf Warthmann is an academic researcher from ETH Zurich. The author has contributed to research in topics: Dolomite & Carbonate. The author has an hindex of 13, co-authored 18 publications receiving 2134 citations. Previous affiliations of Rolf Warthmann include École Polytechnique Fédérale de Lausanne & University of Granada.

Bacterially induced dolomite precipitation in anoxic culture experiments

Abstract: To study the process of microbial-mediated dolomite formation, growth experiments were carried out with selected bacterial cultures under anoxic environmental conditions simulating those found in Lagoa Vermelha, a hypersaline lagoon in Brazil where dolomite precipitation occurs. Specifically, we report the isolation of a particular strain of sulfate-reducing bacteria, LVform6, from Lagoa Vermelha sediment, which apparently promotes the formation of nonstoichiometric dolomite. Sulfate-reducing bacteria grown in a synthetic liquid medium produced dolomite during 30 days incubation at 30 °C. The precipitates have morphologies similar to those observed in Lagoa Vermelha sediment. Our results demonstrate that sulfate-reducing bacteria can influence dolomite precipitation under controlled lowtemperature, anoxic conditions, and imply that anaerobic microorganisms can play an important role in carbonate sedimentation. They may have been particularly significant in Earth's earliest history when a more reducing atmosphere existed.

Calibration of the δ18O paleothermometer for dolomite precipitated in microbial cultures and natural environments

Abstract: Decades of various and numerous isotopic studies to interpret the environmental conditions of dolomite formation proved to be inconclusive because the temperature-dependent oxygen isotope fractionation factor between dolomite and the solution from which it precipitated could not be determined experimentally at low temperatures. With the discovery of bacteria that mediate the precipitation of dolomite, it is now possible to overcome kinetic barriers and precipitate dolomite under controlled temperature conditions in culture experiments. Herein we report on the results of microbial experiments that have enabled us to calibrate the dolomite-water oxygen isotope fractionation factor and provide a paleothermometer to evaluate conditions of ancient dolomite formation. The temperature (T) dependence of the fractionation is defined by the equation: 1000 In α d o l o m i t e - w a t e r = 2.73 X 10 6 T - 2 + 0.26.

Sulphate-reducing bacteria induce low-temperature Ca-dolomite and high Mg-calcite formation

Abstract: In this study, we demonstrate that sulphate-reducing bacteria induce anoxic low-temperature Ca-dolomite formation both in situ in Lagoa Vermelha and Brejo do Espinho, two neighbouring, dolomite-precipitating hypersaline lagoons in Brazil, and in laboratory culture experiments. The metabolic activity of sulphate-reducing bacteria facilitates dolomite formation under anoxic conditions, as demonstrated with experiments using dialysis bags. Overall changes in the chemical conditions of the medium exclusively, without the presence of bacteria, did not result in carbonate precipitation. Only pure cultures of metabolizing sulphate-reducing bacteria induced Ca-dolomite and high Mg-calcite precipitates, indicating that the carbonate nucleation takes place in the locally changed microenvironment around the sulphate-reducing bacterial cells. Not all pure strains, however, produced Ca-dolomite under similar conditions, suggesting that the bacterial metabolism, activity and the rate of mineral precipitation have an influence on the type of carbonate formed.

Dolomite formation within microbial mats in the coastal sabkha of Abu Dhabi (United Arab Emirates)

Abstract: Microbial mediation is the only demonstrated mechanism to precipitate dolomite under Earth surface conditions. A link between microbial activity and dolomite formation in the sabkha of Abu Dhabi has, until now, not been evaluated, even though this environment is cited frequently as the type analogue for many ancient evaporitic sequences. Such an evaluation is the purpose of this study, which is based on a geochemical and petrographic investigation of three sites located on the coastal sabkha of Abu Dhabi, along a transect from the intertidal to the supratidal zone. This investigation revealed a close association between microbial mats and dolomite, suggesting that microbes are involved in the mineralization process. Observations using scanning electron microscopy equipped with a cryotransfer system indicate that authigenic dolomite precipitates within the exopolymeric substances constituting the microbial mats. In current models, microbial dolomite precipitation is linked to an active microbial activity that sustains high pH and alkalinity and decreased sulphate concentrations in pore waters. Such models can be applied to the sabkha environment to explain dolomite formation within microbial mats present at the surface of the intertidal zone. By contrast, these models cannot be applied to the supratidal zone, where abundant dolomite is present within buried mats that no longer show signs of intensive microbial activity. As no abiotic mechanism is known to form dolomite at Earth surface conditions, two different hypotheses can reconcile this result. In a first scenario, all of the dolomite present in the supratidal zone formed in the past, when the mats were active at the surface. In a second scenario, dolomite formation continues within the buried and inactive mats. In order to explain dolomite formation in the absence of active microbial metabolisms, a revised microbial model is proposed in which the mineral-template properties of exopolymeric substances play a crucial role.

Microbial fossilization in carbonate sediments: a result of the bacterial surface involvement in dolomite precipitation

Abstract: Recent dolomitic sediment samples from Lagoa Vermelha, Brazil, were examined microscopically to study the process of bacterial fossilization in carbonate sediments. Bacteria-like bodies were intimately associated with carbonate mineral surfaces, and coatings on the former demonstrate the calcification of single bacterial cells. The bacterial fossilization process in Lagoa Vermelha sediments was simulated in the laboratory by cultivation of mixed and pure cultures of sulphate-reducing bacteria, which were isolated from the Lagoa Vermelha sediments. These cultures produced carbonate minerals that were studied to provide insight into the initiation of the fossilization process. In mixed culture experiments, bacterial colonies became calcified, whereas in pure culture experiments, single bacterial cells were associated with dolomite surfaces. Dolomite nucleated exclusively in bacterial colonies, intimately associated with extracellular organic matter and bacterial cells. Electrophoretic mobility measurements of the bacterial cells in electrolyte solutions demonstrated the specific adsorption of Ca 2 + and Mg 2 + onto the cell surfaces, indicating the role of the bacterial surface in carbonate nucleation and bacterial fossilization. The affinity of the cells for Mg 2 + was related to the capability of the strains to mediate dolomite formation. Combined with sulphate uptake, which dissociates the [MgSO 4 ] o ion pair and increases the Mg 2 + availability, the concentration of Mg 2 + ions in the microenvironment around the cells, where the conditions are favourable for dolomite precipitation, may be the key to overcome the kinetic barrier to dolomite formation. These results demonstrate that bacterial fossilization is a consequence of the cell surface involvement in carbonate precipitation, implying that fossilized bacterial bodies can be used as a tool to recognize microbially mediated carbonates.

Magnetic nanoparticles: design and characterization, toxicity and biocompatibility, pharmaceutical and biomedical applications.

Abstract: Biocompatibility, Pharmaceutical and Biomedical Applications L. Harivardhan Reddy,†,‡ Jose ́ L. Arias, Julien Nicolas,† and Patrick Couvreur*,† †Laboratoire de Physico-Chimie, Pharmacotechnie et Biopharmacie, Universite ́ Paris-Sud XI, UMR CNRS 8612, Faculte ́ de Pharmacie, IFR 141, 5 rue Jean-Baptiste Cleḿent, F-92296 Chat̂enay-Malabry, France Departamento de Farmacia y Tecnología Farmaceútica, Facultad de Farmacia, Campus Universitario de Cartuja s/n, Universidad de Granada, 18071 Granada, Spain ‡Pharmaceutical Sciences Department, Sanofi, 13 Quai Jules Guesdes, F-94403 Vitry-sur-Seine, France

Principles of Sedimentology and Stratigraphy

Abstract: 1. Weathering and Soils 2. Transport and Deposition of Siliciclastic Sediment 3. Sedimentary Textures 4. Sedimentary Structures 5. Siliciclastic Sedimentary Rocks 6. Carbonate Sedimentary Rocks 7. Other Chemical/Biochemical and Carbonaceous Sedimentary Rocks 8. Continental (Terrestrial) Environments 9. Marginal-Marine Environments 10. Siliciclastic Marine Environments 11. Carbonate and Evaporite Environments 12. Lithostratigraphy 13. Seismic, Sequence, and Magnetic Stratigraphy 14. Biostratigraphy 15. Chronostratigraphy and Geologic Time 16. Basin Analysis, Tectonics, and Sedimentation

Bacteria and archaea on Earth and their abundance in biofilms

Abstract: Biofilms are a form of collective life with emergent properties that confer many advantages on their inhabitants, and they represent a much higher level of organization than single cells do. However, to date, no global analysis on biofilm abundance exists. We offer a critical discussion of the definition of biofilms and compile current estimates of global cell numbers in major microbial habitats, mindful of the associated uncertainty. Most bacteria and archaea on Earth (1.2 × 1030 cells) exist in the ‘big five’ habitats: deep oceanic subsurface (4 × 1029), upper oceanic sediment (5 × 1028), deep continental subsurface (3 × 1029), soil (3 × 1029) and oceans (1 × 1029). The remaining habitats, including groundwater, the atmosphere, the ocean surface microlayer, humans, animals and the phyllosphere, account for fewer cells by orders of magnitude. Biofilms dominate in all habitats on the surface of the Earth, except in the oceans, accounting for ~80% of bacterial and archaeal cells. In the deep subsurface, however, they cannot always be distinguished from single sessile cells; we estimate that 20–80% of cells in the subsurface exist as biofilms. Hence, overall, 40–80% of cells on Earth reside in biofilms. We conclude that biofilms drive all biogeochemical processes and represent the main way of active bacterial and archaeal life. In this Analysis article, Flemming and Wuertz calculate the total number of bacteria and archaea on Earth and estimate the fraction that lives in biofilms. They propose that biofilms are the most prominent and influential type of microbial life.

Key roles of pH and calcium metabolism in microbial carbonate precipitation

Abstract: This paper reviews the general mechanismsof microbial carbonate precipitation and offersan alternative view on the role of calciummetabolism in this process, as well as on theoccurrence of species- and environment-specificcalcification.