Routes of phlogopite weathering by three fungal strains

Naturwissenschaften, 2008

Fungal activity is thought to play a direct and effective role in the breakdown and dissolution of primary minerals and in the synthesis of clay minerals in soil environments, with important consequences for plant growth and ecosystem functioning. We have studied primary mineral weathering in volcanic soils developed on trachydacite in southern Tuscany using a combination of qualitative and quantitative mineralogical and microbiological techniques. Specifically, we characterized the weathering and microbiological colonization of the magnetically separated ferromagnesian minerals (biotite and orthopyroxene) and non-ferromagnesian constituents (K-feldspar and volcanic glass) of the coarse sand fraction (250-1,000 µm). Our results show that in the basal horizons of the soils, the ferromagnesian minerals are much more intensively colonized by microorganisms than K-feldspar and glass, but that the composition of the microbial communities living on the two mineral fractions is similar. Moreover, X-ray diffraction, optical and scanning electron microscope observations show that although the ferromagnesian minerals are preferentially associated with an embryonic form of the clay mineral halloysite, they are still relatively fresh. We interpret our results as indicating that in this instance microbial activity, and particularly fungal activity, has not been an effective agent of mineral weathering, that the association with clay minerals is indirect, and that fungal weathering of primary minerals may not be as important a source of plant nutrients as previously claimed.

Colloids and Surfaces a Physicochemical and Engineering Aspects, 1997

Organic acids and their anions (for brevity we shall use the term "'acids" to include bothJ may affect mineral weathering rates by at least three mechanisms: by changing the dissolution rate far from equilibrium through decreasing solution pH or forming complexes with cations at the mineral surface; by affecting the saturation state of the solution with respect to the mineral; and by affecting the speciation in solution of ions such as A1-~ + that themselves affect mineral dissolution rate. In this paper we review the effects of organic acids on the dissolution rates of silicate minerals, particularly feldspars, under conditions approximating the natural weathering environment 25 C, pH 4 7 and with concentrations of organic acids comparable to those measured in soil solutions. Feldspar dissolution rates far from equilibrium increase with decreasing pH below pH 4 5. They appear to be independent ofpH between pH 4-5 and about 8, and above pH 8 feldspar dissolution rates increase with increasing pH. Small chelating ligands such as oxalate appear to accelerate feldspar dissolution through complexation of At at the surface of the mineral. Feldspar dissolution rates in the presence of 1 mM oxalic acid show efl'ects ranging from no enhancement to enhancements of a factor of 15, depending upon the data set, pH, and aluminum content of the mineral: there is a great deal of scatter in the available data. In general, concentrations of oxalate of the order of 1 mM are necessary to cause a significant effect. Humic acids do not appear to increase feldspar dissolution rates significantly. Dissolution rates must decrease as the solution approaches saturation with respect to the primary phase Iflae chemical affinity effect). Organic acids will influence chemical affinity by complexing A1 (and possibly other elements) in solution and hence decreasing the chemical activity of A13+. There are essentially no data on the effect of chemical affinity on feldspar dissolution rate at 25':'C and mildly acid pH, so it is hard to evaluate the importance of organic acids in accelerating silicate dissolution through the chemical affinity effect. The effect of complexation of dissolved A1 does not appear to be an important determinant of silicate dissolution rates in nature. Observed rates of silicate weathering in the field are typically much slower than predicted from laboratory experiments far from equilibrium, suggesting control by transport of solutes between "'micropores" and "'macropores'" I"micropores'" include fractures and crystal defects within grains). If such transport is rate-controlling, analysis of the effecl of organic acids on weathering rates in nature in terms of dissolution rates far fiom equilibrium may be misleading.

American Mineralogist, 1998

Mineral dissolution experiments using batch cultures of soil and groundwater bacteria were monitored with solution chemistry and various microscopic techniques to determine the effects of these organisms on weathering reactions. Several strains of bacteria produced organic and inorganic acids and extracellular polymers in culture, increasing the release of cations from biotite (Si, Fe, Al) and plagioclase feldspar (Si, Al) by up to two orders of magnitude compared to abiotic controls. Microbial colonies on mineral grains were examined by cryo-scanning electron microscopy (cryo-SEM), confocal scanning laser microscopy (CSLM), and epifluorescence microscopy. Bacteria colonized all mineral surfaces, often preferentially along cleavage steps and edges of mineral grains. Low-voltage high-resolution cryo-SEM of high-pressure cryofixed and partially freeze-dried colonized minerals showed many bacteria attached by extracellular polymers of unknown composition. These biofilms covered much larger areas of the mineral surfaces than bacterial cells alone. Mineral surfaces where bacteria and extracellular polymers occurred appeared more extensively etched than surrounding uncolonized surfaces. CSLM was used to observe microbial colonization of biotite and to measure pH in microenvironments surrounding living microcolonies using a ratiometric pH-sensitive fluorescent dye set. A strain of bacteria (B0693 from the U.S. Department of Energy Subsurface Microbial Culture Collection) formed large attached microcolonies, both on the outer (001) surface and within interlayer spaces as narrow as 1 m. Solution pH decreased from near neutral at the mineral surface to 3-4 around microcolonies living within confined spaces of interior colonized cleavage planes. However, no evidence of pH microgradients surrounding exterior microcolonies was noted.

Scientific Reports, 2022

Nutrient foraging by fungi weathers rocks by mechanical and biochemical processes. Distinguishing fungal-driven transformation from abiotic mechanisms in soil remains a challenge due to complexities within natural field environments. We examined the role of fungal hyphae in the incipient weathering of granulated basalt from a three-year field experiment in a mixed hardwood-pine forest (S. Carolina) to identify alteration at the nanometer to micron scales based on microscopy-tomography analyses. Investigations of fungal-grain contacts revealed (i) a hypha-biofilm-basaltic glass interface coinciding with titanomagnetite inclusions exposed on the grain surface and embedded in the glass matrix and (ii) native dendritic and subhedral titanomagnetite inclusions in the upper 1-2 µm of the grain surface that spanned the length of the fungal-grain interface. We provide evidence of submicron basaltic glass dissolution occurring at a fungal-grain contact in a soil field setting. An example of how fungalmediated weathering can be distinguished from abiotic mechanisms in the field was demonstrated by observing hyphal selective occupation and hydrolysis of glass-titanomagnetite surfaces. We hypothesize that the fungi were drawn to basaltic glass-titanomagnetite boundaries given that titanomagnetite exposed on or very near grain surfaces represents a source of iron to microbes. Furthermore, glass is energetically favorable to weathering in the presence of titanomagnetite. Our observations demonstrate that fungi interact with and transform basaltic substrates over a threeyear time scale in field environments, which is central to understanding the rates and pathways of biogeochemical reactions related to nuclear waste disposal, geologic carbon storage, nutrient cycling, cultural artifact preservation, and soil-formation processes. The weathering of basalts and natural glasses has wide-ranging implications for our society and beyond including the supply of life-supporting nutrients from rocks to the environment 1. Over geologic timescales, the global consumption of atmospheric carbon dioxide by basaltic weathering sequesters carbon into stable carbonate rock, which is twice as efficient as weathering carbonate rocks themselves 2,3. The coevolution of the geospherebiosphere on early Earth was also linked to the weathering of basalt and the formation of clay minerals 4,5. With respect to the study of planetary systems, the degree of basaltic alteration observed on Mars contributes to our understanding of astrobiology and the evolution of extraterrestrial landscapes 6-8. The pathways and mechanisms that control the dissolution of synthetic glasses produced for the storage of radionuclides in geologic repositories has also been well-studied 9,10. Thus, assessing the biotic and abiotic drivers of basalt and glass weathering in natural Earth systems, including soils, remains of paramount importance for recognizing and predicting long-term ecosystem response to changes in global climate 11,12 , identifying lithologic controls on global carbon cycling 2,13 , or detecting mineralogical biosignatures that may provide evidence for past, present, and future life on other planets 14-16. Emphasis has been placed on the importance of micro-to nanoscale investigations for disentangling the intricacies of microbially-mediated or abiotically-driven weathering mechanisms 17,18

Geochimica et Cosmochimica Acta, 2015

Biotite dissolution rates were determined at 25°C, at pH 2-6, and as a function of mineral composition, grain size, and aqueous organic ligand concentration. Rates were measured using both open-and closed-system reactors in fluids of constant ionic strength. Element release was non-stoichiometric and followed the general trend of Fe, Mg > Al > Si. Biotite surface area normalised dissolution rates (r i ) in the acidic range, generated from Si release, are consistent with the empirical rate law:

Applied and Environmental Microbiology, 2013

ABSTRACTThe bioavailability of metals in soil is often cited as a limiting factor of phytoextraction (or phytomining). Bacterial metabolites, such as organic acids, siderophores, or biosurfactants, have been shown to mobilize metals, and their use to improve metal extraction has been proposed. In this study, the weathering capacities of, and Ni mobilization by, bacterial strains were evaluated. Minimal medium containing ground ultramafic rock was inoculated with either of twoArthrobacterstrains: LA44 (indole acetic acid [IAA] producer) or SBA82 (siderophore producer, PO4solubilizer, and IAA producer). Trace elements and organic compounds were determined in aliquots taken at different time intervals after inoculation. Trace metal fractionation was carried out on the remaining rock at the end of the experiment. The results suggest that the strains act upon different mineral phases. LA44 is a more efficient Ni mobilizer, apparently solubilizing Ni associated with Mn oxides, and this ap...

Clays and Clay Minerals, 1998

Microbial reduction of clay mineral structural Fe(III) decreases the swelling of nontronite gels, most importantly at intermediate oxidation states (40 to 80 cmoi Fe(II) kg -1 clay). The purpose of this study was to establish whether microbial reduction of structural Fe(III) decreased the swelling of other Fe-bearing smectites and to discern the influence that organic compounds of microbial origin (bacterial cells, cell fragments and/or exudates) may have on clay swelling and texture. Structural Fe(III) was reduced by incubating smectite suspensions with either a combination of Pseudomonas bacteria or a mixture of anaerobic bacteria. The influence of organics on clay swelling was estimated on smectites suspended in either organic or inorganic media in the absence of bacteria. The gravimetric water content of the reduced clay gels equilibrated at various applied pressures was recorded as a function of Fe oxidation state. Transmission electron microscopy (TEM) was employed to determine the influence of bacteria and type of media on the texture of reduced smectite gels. Reduction of structural Fe(III) by bacteria decreased the swelling pressure of all Fe-bearing smectites. Increased clay swelling, due to the presence of organics (organic medium, exudates or cell fragments), was correlated to the total Fe content, the extent of structural Fe reduction, as well as the initial swelling characteristics of the Fe-bearing smectites. High structural Fe(II) contents (>50 cmol Fe(II) kg -~) resulted in increased attractive forces between clay platelets that decreased clay swelling, even in organic medium suspensions. Microbial reduction resulted in increased face-face association of individual clay layers, forming larger and more distinct crystallite subunits than in nonreduced clay gels. But, perhaps more importantly, microbial reduction of structural Fe(III) resulted in an increased association between crystallite subunits and, thus, an overall larger particle size and pore size distribution, due to the interaction of bacteria ceils, cell fragments and organic exudates.

Hydrometallurgy, 2001

Microbiological weathering of a research-grade mica mineral, phlogopite, was studied using ferrous sulfate media that were inoculated with an acidophilic iron-oxidizing bacterium, Thiobacillus ferrooxidans. Weathering due to dissolution was monitored by analysis of Si, Al, Fe, K, Na, Mg, and Ca in the leach solutions and in chemical controls at pH 1.0, 1.5 and Ž . 2.0. Structural alterations of phlogopite were analyzed by X-ray diffraction. At pH 2, the oxidation of Fe II by T. ferrooxidans was accompanied by the formation of jarosite within 7 days of incubation at 228C. The precipitation of jarosite Ž . was coupled with partial alteration of phlogopite to vermiculite and an interstratified mixed-layer phlogopitervermiculite. Similar results were obtained with chemical controls containing 120 mM ferric sulfate. The data suggested that K incorporated into jarosite was released from interlayer positions in phlogopite; thus, jarosite constituted a sink for K. The formation of jarosite and expansible layer silicate phases was pH-dependent. At pH -1.5, jarosite was not formed and phlogopite weathering was due to chemical dissolution without detectable structural alteration. q

Mineralogical Magazine, 1973

The behaviour of iron in the weathering of biotite in a sedentary soil profile developed on appinite has been investigated using the M6ssbauer effect. Both Fe z+ and Fe a+ in sites with cis and trans hydroxyl groups were observed at various stages in the weathering sequence. The results indicate that there is little or no ordering of the octahedral cations in the fresh biotite and hydrobiotite, but in the more weathered interstratifled vermiculite-chlorite samples Fe a+ concentrates in the more distorted sites. No evidence was obtained for the presence of an anisotropic recoil-free fraction.

Addressing the paucity of reliable, robust studies into the weathering effect exerted by biota onto rocks and minerals: mineral weathering by the moss Physcomitrella patens was measured in a novel in vitro microcosm study.