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GERNOT ARP CHRISTIAN OSTERTAG‐HENNING SELÇÜK YÜCEKENT JOACHIM REITNER VOLKER THIEL 《Sedimentology》2008,55(5):1227-1251
Fossil stromatolites may reveal information about their hydrochemical palaeoenvironment, provided that assignment to a specific microbial community and a corresponding biogeochemical mechanism of formation can be made. Tithonian stromatolites of the Münder Formation at Thüste, north Germany, have traditionally been considered as formed by intertidal cyanobacterial communities. However, thin sections of the stromatolites show elongated angular traces of former gypsum crystals in a dense arrangement, but no algal or cyanobacterial filament traces. Moreover, high Fe2+ and Mn2+ contents, oxygen‐isotope and sulphur‐isotope ratios of carbonate‐bound sulphates, and sulphurized hydrocarbon biomarkers of the stromatolitic carbonate indicate that CaCO3 precipitation occurred near the oxic–anoxic interface as a result of intensive bacterial sulphur cycling rather than photosynthetic activity. Furthermore, anaerobic oxidation of methane by Archaea may have driven CaCO3 precipitation in deeper parts of the biofilm community, as reflected by high concentrations of squalane with a strongly negative δ13C in conjunction with evaporite pseudomorphs showing extremely low δ13CCarb ratios. Consequently, the Thüste stromatolites are now interpreted as having initially formed by gypsum impregnation of biofilms. Subsequently, early Mg‐calcitic calcitization within the biofilms occurred because of combined bacterial iron, manganese and sulphate reduction, with an increasing contribution of anaerobic oxidation of methane with depth. This model plausibly explains the prominent preservation of signals derived from oxygen‐independent metabolic pathways, whereas virtually no geochemical record exists for an aerobic community that may, nevertheless, have prevailed at the stromatolite surface. Photic‐zone stromatolites with a prominent signal of anaerobic oxidation of methane may be common in, and indicative of, oxygen‐depleted sulphate‐bearing environments with high rates of methane production, conditions that possibly were fulfilled at the Archaean to Proterozoic transition. 相似文献
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Etch pit formation on iron silicate surfaces during siderophore-promoted dissolution 总被引：1，自引：0，他引：1
Understanding the effects of microbiota on mineral alteration requires the ability to recognize evidence of bacteria-promoted dissolution on mineral surfaces. Although siderophores are known to promote mineral dissolution, their effects on mineral surfaces are not well known. We have utilized atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Mirau vertical scanning interferometry (VSI) to investigate surfaces after incubation with the siderophore desferrioxamine-B mesylate (DFAM) and under colonies of bacteria. Iron-silicate glass planchets chemically similar to hornblende were incubated in buffered growth medium with siderophore-producing bacteria (Bacillus sp.) for 46 days with parallel abiotic experiments conducted with and without 240 μM DFAM, with and without 0.01 g l− 1 of microbially produced extracellular polysaccharides (EPS, alginate or xanthan gum). Some glass planchets were protected by dialysis tubing from direct contact with the EPS. Weekly sampling and analysis of all filtered sample solutions showed negligible Fe and Al release in the control experiments and significant release of Fe and Al in the presence of DFAM, with negligible changes in pH. Concentration of Fe in the filtered solutions after incubation with bacteria was below detection, consistent with uptake of Fe by cells. Release of Fe, Al, and Si in control, xanthan-only, and alginate-only experiments was negligible. Release of these elements was enhanced in all experiments containing DFAM, and greatest in alginate + DFAM experiments.
AFM and VSI analyses reveal widespread, small etch pits and greater root mean squared roughness on siderophore-exposed surfaces and fewer, localized, larger etch pits on bacteria-exposed surfaces. This is the first documented case of etch pit development during siderophore-promoted dissolution. Roughness was not affected by the growth medium, alginate, or xanthan gum alone. The roughness trends among samples correlate with trends in Fe depletion documented by XPS. Enhanced dissolution and roughness cannot be attributed to direct contact with EPS because no significant chemical or physical differences were observed between surfaces directly exposed to EPS and those protected by dialysis tubing. Acetate released from the EPS may have enhanced the siderophore-promoted dissolution. Siderophores produced by Bacillus sp. may be responsible for some of the ‘biopits.’ The difference in size and distribution of the biopits may be related to colonization. 相似文献
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Microbial signatures in peritidal siliciclastic sediments: a catalogue 总被引：12，自引：0，他引：12
A catalogue of microbial structural signatures is presented, based upon the coupling of fundamental biogeochemical–microbial processes and local morphogenetic determinants. It summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones (temperate humid: Mellum Island, southern North Sea; subtropical arid: coast of southern Tunisia). Textural geometries reveal a high structural diversity, but their determinants are primarily based upon six major parameters: (1) intrinsic biofactors: structural diversification of sedimentary microbial films and mats inherent in the organisms, i.e. their construction morphology, growth, taxis and behaviour, and local abundance of specific morphotypes. Most prominent are the ensheathed filamentous cyanobacteria Microcoleus chthonoplastes and Lyngbya aestuarii, and the sheathless filamentous cyanobacterium Oscillatoria limosa. (2) Biological response to physical disturbances: sediment supply, erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats. (3) Trapping/binding effects: physicobiological processes give rise to grain orientations and wavy to lenticular lamina, lamina‐specific grain arrangements and ‘sucrose’ calcium carbonate accumulations. (4) Secondary physical deformation of biogenic build‐ups: mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures. (5) Post‐burial processes: textural fabrics that evolve from mechanical effects of gas formation from decaying mats, and features related to the formation of authigenic minerals (calcium carbonates, calcium sulphates, pyrite). (6) Bioturbation and grazing: post‐depositional structures, such as Skolithos‐type dwellings, traces of burrowing insects, gastropod grazing traces and faecal pellets. In synopsis, the catalogue firstly comprises a sound set of ubiquitous signatures. This uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings. The catalogue secondly documents signatures that are extremely sensitive to tidal position, hydrodynamic regime and overall climatic conditions. These kinds of signature indicate narrow facies zones, which often coincide with the activity or dominance zones of certain organisms. An overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings. 相似文献
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This study focused on clogging processes and on the benthic microalgal and meiofaunal assemblage in the sandy littoral zone of Lake Tegel, which are significantly involved in bank filtration, in a long-term. Our approach combined field studies and “in situ” experiments to highlight the structure of the biological active filter zone as well as the mechanisms and effects of clogging in the interstices that influence the infiltration process.Campaigns to measure “in situ” infiltration rates and hydraulic potential were conducted monthly from March 2004 to April 2005. Meiofaunal abundances and fine particulate organic matter (FPOM) were determined every 6 weeks in freeze cores down to depths of 50 cm. In parallel, concentrations of carbon, nitrogen and chlorophyll a were measured in samples of unfrozen sediment cores, that were divided in 1-cm steps down to depths of ≥10 cm. Similar sediment profiles were generated for analysis of colloidal carbohydrates, extracellular polymeric substances (EPS) and proteins between December 2005 and June 2006. Electron microscopy was used to visualize biofilm structure. Long-term experiments with natural FPOM and melamine resin particles as fluorescent tracers were performed to study “in situ” particle retention and transport, respectively. Additionally seston input was quantified during a 1-week period in April 2005.Infiltration rates showed a high temporal and spatial variability, but were not correlated with hydraulic conductivities as hydraulic gradients changed a lot. Likewise a correlation between infiltration rates and hydraulic potentials was not observed, indicating clogging processes. These are triggered to a high extend by biological compounds. In addition, seston input and intermittent gas intrusion are considered to reduce the hydraulic conductivity considerably. No significant “in situ” transport of inert natural fluorescent tracers was observed. However, a complete and permanent clogging of the sandy sediment does not occur, and daily infiltration rates of 0.7-27 L m−2 h−1 (mean 9 L m−2 h−1) guarantee a sufficient water supply by bank filtration for decades. 相似文献
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Mine tailings may be remediated using metal tolerant microorganisms as they may solve the limiting conditions for healthy
development of plants (i.e., low organic mater content and poor physical conditions). The aim of this study was to investigate
the consequences of microbial colonization on the chemical speciation of trace metals. Surface samples from the Valenciana
mine tailings (Guanajuato, Mexico) were used for long-term bioassays (BA), which consisted in the promotion of microorganisms,
development on tailings material under stable laboratory conditions (humidity, temperature, and light exposure). A five-step
sequential extraction method (exchangeable, carbonate/specifically adsorbed, Fe–Mn oxides, organic matter (OM)/sulfide, and
residual fractions) was performed before and after BA. Extraction solutions and leachates were analyzed by inductively coupled
plasma-mass spectrometry. OM content, cationic exchange capacity, and pH values were also assessed before and after BA. The
results indicate that trace elements are generally present in nonresidual fractions, mainly in the Fe–Mn oxides fraction.
The concentration of total Zn, As, Se, Pb, and exchangeable Cu and Pb is above the recommendable limits for soils. Despite
the high bioavailability of the former elements, biofilms successfully colonized the tailing samples during the BA. Cyanobacteria
and green algae, heterotrophic fungi, aerobic bacteria, and anaerobic bacteria composed the developed biofilms. Chemical controls
of trace elements could be attributed to absorption onto inorganic complexes (carbonates, metal oxides), while biofilm occurrence
seems to enhance complexation and immobilization of Cr, Ni, Cu, Zn, As, and Pb. The biofilm developed does not increase the
bioavailable forms and the leaching of the trace elements, but significantly improves the OM contents (natural fertilization).
The results suggest that biofilms are useful during the first steps of the mine tailings remediation. 相似文献
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We develop a one-equation non-equilibrium model to describe the Darcy-scale transport of a solute undergoing biodegradation in porous media. Most of the mathematical models that describe the macroscale transport in such systems have been developed intuitively on the basis of simple conceptual schemes. There are two problems with such a heuristic analysis. First, it is unclear how much information these models are able to capture; that is, it is not clear what the model's domain of validity is. Second, there is no obvious connection between the macroscale effective parameters and the microscopic processes and parameters. As an alternative, a number of upscaling techniques have been developed to derive the appropriate macroscale equations that are used to describe mass transport and reactions in multiphase media. These approaches have been adapted to the problem of biodegradation in porous media with biofilms, but most of the work has focused on systems that are restricted to small concentration gradients at the microscale. This assumption, referred to as the local mass equilibrium approximation, generally has constraints that are overly restrictive. In this article, we devise a model that does not require the assumption of local mass equilibrium to be valid. In this approach, one instead requires only that, at sufficiently long times, anomalous behaviors of the third and higher spatial moments can be neglected; this, in turn, implies that the macroscopic model is well represented by a convection–dispersion–reaction type equation. This strategy is very much in the spirit of the developments for Taylor dispersion presented by Aris (1956). On the basis of our numerical results, we carefully describe the domain of validity of the model and show that the time-asymptotic constraint may be adhered to even for systems that are not at local mass equilibrium. 相似文献
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Christopher T. Perry 《Sedimentology》1999,46(1):33-45
Micrite envelopes are a common feature in carbonate sediments and are typically associated with the micrite filling of borings produced by microendolithic organisms. These are referred to as 'destructive micrite envelopes' and have long been recognized as reflecting an important early diagenetic process. Recent analysis of sediments collected from back-reef environments at Discovery Bay, north Jamaica, however, has demonstrated 'envelope' formation on the surfaces of carbonate grains, clearly distinct from the micrite filling of microborings. Such constructive envelopes occur almost exclusively in sediments from grass-bed environments and are always intimately associated with 'biofilms' comprising abundant mucilage, cyanobacteria, bacteria and diatoms. It is suggested that these envelopes represent a product of both biologically mediated micrite precipitation (occurring within the biofilm mucilage and around the biofilm components, i.e. cyanobacteria and diatoms) and associated trapping of carbonate mud and fine-grained sediment. Their recognition only within grass-bed sediments may enable their use as a diagnostic feature of grass-bed environments or vegetation-stabilized substrates in the rock record. 相似文献
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