Sulfate-reducing bacteria-dominated biofilms that precipitate ZnS in a subsurface circumneutral-pH mine drainage system

The microbial diversity of ZnS-forming biofilms in 8 degrees C, circumneutral-pH groundwater in tunnels within the abandoned Piquette Zn, Pb mine (Tennyson, Wisconsin, USA) has been investigated by molecular methods, fluorescence in situ hybridization (FISH), and cultivation techniques. These biofilms are growing on old mine timbers that generate locally anaerobic zones within the mine drainage system. Sulfate-reducing bacteria (SRB) exclusively of the family Desulfobacteriaceae comprise a significant fraction of the active microbiota. Desulfosporosinus strains were isolated, but could not be detected by molecular methods. Other important microbial clusters belonged to the beta-, gamma-, and epsilon-Proteobacteria, the Cytophaga/Flexibacter/Bacteroides-group (CFB), Planctomycetales, Spirochaetales, Clostridia, and green nonsulfur bacteria. Our investigations indicated a growth dependence of SRB on fermentative, cellulolytic, and organic acid-producing Clostridia. A few clones related to sulfur-oxidizing bacteria were detected, suggesting a sulfur cycle related to redox gradients within the biofilm. Sulfur oxidation prevents sulfide accumulation that would lead to precipitation of other sulfide phases. FISH analyses indicated that Desulfobacteriaceae populations were not early colonizers in freshly grown and ZnS-poor biofilms, whereas they were abundant in older, naturally established, and ZnS-rich biofilms. Gram-negative SRB have been detected in situ over a period of 6 months, supporting the important role of these organisms in selective ZnS precipitation in Tennyson mine. Results demonstrate the complex nature of biofilms responsible for in situ bioremediation of toxic metals in a subsurface mine drainage system.

Energetics of nanocrystalline TiO2

The energetics of the TiO(2) polymorphs (rutile, anatase, and brookite) were studied by high temperature oxide melt drop solution calorimetry. Relative to bulk rutile, bulk brookite is 0.71 +/- 0.38 kJ/mol (6) and bulk anatase is 2.61 +/- 0.41 kJ/mol higher in enthalpy. The surface enthalpies of rutile, brookite, and anatase are 2.2 +/- 0.2 J/m(2), 1.0 +/- 0.2 J/m(2), and 0.4 +/- 0.1 J/m(2), respectively. The closely balanced energetics directly confirm the crossover in stability of nanophase polymorphs inferred by Zhang and Banfield (7). An amorphous sample with surface area of 34,600 m(2)/mol is 24.25 +/- 0.88 kJ/mol higher in enthalpy than bulk rutile.

Arsenite oxidation and arsenate respiration by a new Thermus isolate

A new microbial strain was isolated from an arsenic-rich terrestrial geothermal environment. The isolate, designated HR13, was identified as a Thermus species based on 16S rDNA phylogenetic relationships and close sequence similarity within the Thermus genus. Under aerobic conditions, Thermus HR13 was capable of rapidly oxidizing inorganic As(III) to As(V). As(III) was oxidized at a rate approximately 100-fold greater than abiotic rates. Metabolic energy was not gained from the oxidation reaction. In the absence of oxygen, Thermus HR13 grew by As(V) respiration coupled with lactate oxidation. The ability to oxidize and reduce arsenic has not been previously described within the Thermus genus.

Rapid arsenite oxidation by Thermus aquaticus and Thermus thermophilus: field and laboratory investigations

Thermus aquaticus and Thermus thermophilus, common inhabitants of terrestrial hot springs and thermally polluted domestic and industrial waters, have been found to rapidly oxidize arsenite to arsenate. Field investigations at a hot spring in Yellowstone National Park revealed conserved total arsenic transport and rapid arsenite oxidation occurring within the drainage channel. This environment was heavily colonized by Thermus aquaticus. In laboratory experiments, arsenite oxidation by cultures of Thermus aquaticus YT1 (previously isolated from Yellowstone National Park) and Thermus thermophilus HB8 was accelerated by a factor of over 100 relative to a biotic controls. Thermus aquaticus and Thermus thermophilus may therefore play a large and previously unrecognized role in determining arsenic speciation and bioavailability in thermal environments.

Mineralogical biosignatures and the search for life on Mars

If life ever existed, or still exists, on Mars, its record is likely to be found in minerals formed by, or in association with, microorganisms. An important concept regarding interpretation of the mineralogical record for evidence of life is that, broadly defined, life perturbs disequilibria that arise due to kinetic barriers and can impart unexpected structure to an abiotic system. Many features of minerals and mineral assemblages may serve as biosignatures even if life does not have a familiar terrestrial chemical basis. Biological impacts on minerals and mineral assemblages may be direct or indirect. Crystalline or amorphous biominerals, an important category of mineralogical biosignatures, precipitate under direct cellular control as part of the life cycle of the organism (shells, tests, phytoliths) or indirectly when cell surface layers provide sites for heterogeneous nucleation. Biominerals also form indirectly as by-products of metabolism due to changing mineral solubility. Mineralogical biosignatures include distinctive mineral surface structures or chemistry that arise when dissolution and/or crystal growth kinetics are influenced by metabolic by-products. Mineral assemblages themselves may be diagnostic of the prior activity of organisms where barriers to precipitation or dissolution of specific phases have been overcome. Critical to resolving the question of whether life exists, or existed, on Mars is knowing how to distinguish biologically induced structure and organization patterns from inorganic phenomena and inorganic self-organization. This task assumes special significance when it is acknowledged that the majority of, and perhaps the only, material to be returned from Mars will be mineralogical.

A new look at microbial leaching patterns on sulfide minerals

Leaching patterns on sulfide minerals were investigated by high-resolution scanning electron microscopy (SEM). Our goal was to evaluate the relative contributions of inorganic surface reactions and reactions localized by attached cells to surface morphology evolution. Experiments utilized pyrite (FeS(2)), marcasite (FeS(2)) and arsenopyrite (FeAsS), and two iron-oxidizing prokaryotes in order to determine the importance of cell type, crystal structure, and mineral dissolution rate in microbially induced pit formation. Pyrite surfaces were reacted with the iron-oxidizing bacterium Acidithiobacillus ferrooxidans (at 25 degrees C), the iron-oxidizing archaeon 'Ferroplasma acidarmanus' (at 37 degrees C), and abiotically in the presence of Fe(3+) ions. In all three experiments, discrete bacillus-sized (1-2 µm) and -shaped (elliptical) pits developed on pyrite surfaces within 1 week of reaction. Results show that attaching cells are not necessary for pit formation on pyrite. Marcasite and arsenopyrite surfaces were reacted with A. ferrooxidans (at 25 degrees C) and 'F. acidarmanus' (at 37 degrees C). Cell-sized and cell-shaped dissolution pits were not observed on marcasite or arsenopyrite at any point during reaction with A. ferrooxidans, or on marcasite surfaces reacted with 'F. acidarmanus'. However, individual 'F. acidarmanus' cells were found within individual shallow (<0.5 µm deep) pits. The size and shape (round rather than elliptical) of the pits conformed closely to the shape of F. acidarmanus (cells) pits on arsenopyrite. We infer these pits to be cell-induced. We attribute the formation of pits readily detectable (by SEM) to the higher reactivity of arsenopyrite compared to pyrite and marcasite under the conditions the experiment was conducted. These pits contributed little to the overall surface topographical evolution, and most likely did not significantly increase surface area during reaction. Our results suggest that overall sulfide mineral dissolution may be dominated by surface reactions with Fe(3+) rather than by reactions at the cell-mineral interface.

Formation of sphalerite (ZnS) deposits in natural biofilms of sulfate-reducing bacteria

Abundant, micrometer-scale, spherical aggregates of 2- to 5-nanometer-diameter sphalerite (ZnS) particles formed within natural biofilms dominated by relatively aerotolerant sulfate-reducing bacteria of the family Desulfobacteriaceae. The biofilm zinc concentration is about 10(6) times that of associated groundwater (0.09 to 1.1 parts per million zinc). Sphalerite also concentrates arsenic (0.01 weight %) and selenium (0.004 weight %). The almost monomineralic product results from buffering of sulfide concentrations at low values by sphalerite precipitation. These results show how microbes control metal concentrations in groundwater- and wetland-based remediation systems and suggest biological routes for formation of some low-temperature ZnS deposits.

Comparison of acid mine drainage microbial communities in physically and geochemically distinct ecosystems

This study presents population analyses of microbial communities inhabiting a site of extreme acid mine drainage (AMD) production. The site is the inactive underground Richmond mine at Iron Mountain, Calif., where the weathering of a massive sulfide ore body (mostly pyrite) produces solutions with pHs of approximately 0.5 to approximately 1.0. Here we used a suite of oligonucleotide probes, designed from molecular data recently acquired from the site, to analyze a number of microbial environments by fluorescent in situ hybridization. Microbial-community analyses were correlated with geochemical and mineralogical data from those environments. The environments investigated were within the ore body and thus at the site of pyrite dissolution, as opposed to environments that occur downstream of the dissolution. Few organism types, as defined by the specificities of the oligonucleotide probes, dominated the microbial communities. The majority of the dominant organisms detected were newly discovered or organisms only recently associated with acid-leaching environments. "Ferroplasma" spp. were detected in many of the communities and were particularly dominant in environments of lowest pH and highest ionic strength. Leptospirillum spp. were also detected in many slime and pyrite-dominated environments. In samples of an unusual subaerial slime, a new uncultured Leptospirillum sp. dominated. Sulfobacillus spp. were detected as a prominent inhabitant in warmer ( approximately 43 degrees C) environments. The information gathered here is critical for determining organisms important to AMD production at Iron Mountain and for directing future studies of this process. The findings presented here also have relevance to the microbiology of industrial bioleaching and to the understanding of geochemical iron and sulfur cycles.

Phylogeny of microorganisms populating a thick, subaerial, predominantly lithotrophic biofilm at an extreme acid mine drainage site

An unusually thick ( approximately 1 cm) slime developed on a slump of finely disseminated pyrite ore within an extreme acid mine drainage site at Iron Mountain, near Redding, Calif. The slime was studied over the period of 1 year. The subaerial form of the slime distinguished it from more typical submerged streamers. Phylogenetic analysis of 16S rRNA genes revealed a diversity of sequences that were mostly novel. Nearest relatives to the majority of sequences came from iron-oxidizing acidophiles, and it appears that iron oxidation is the predominant metabolic characteristic of the organisms in the slime. The most abundant of the 16S rRNA genes detected were from organisms related to Leptospirillum species. The dominant sequence (71% of clones) may represent a new genus. Sequences within the Archaea of the Thermoplasmales lineage were detected. Most of these were only distantly related to known microorganisms. Also, sequences affiliating with Acidimicrobium were detected. Some of these were closely related to "Ferromicrobium acidophilus," and others were affiliated with a lineage only represented by environmental clones. Unexpectedly, sequences that affiliated within the delta subdivision of the Proteobacteria were detected. The predominant metabolic feature of bacteria of this subdivision is anaerobic sulfate or metal reduction. Thus, microenvironments of low redox potential possibly exist in the predominantly oxidizing environments of the slime. These results expand our knowledge of the biodiversity of acid mine drainage environments and extend our understanding of the ecology of extremely acidic systems.

Aggregation-based crystal growth and microstructure development in natural iron oxyhydroxide biomineralization products

Crystals are generally considered to grow by attachment of ions to inorganic surfaces or organic templates. High-resolution transmission electron microscopy of biomineralization products of iron-oxidizing bacteria revealed an alternative coarsening mechanism in which adjacent 2- to 3-nanometer particles aggregate and rotate so their structures adopt parallel orientations in three dimensions. Crystal growth is accomplished by eliminating water molecules at interfaces and forming iron-oxygen bonds. Self-assembly occurs at multiple sites, leading to a coarser, polycrystalline material. Point defects (from surface-adsorbed impurities), dislocations, and slabs of structurally distinct material are created as a consequence of this growth mechanism and can dramatically impact subsequent reactivity.

Characteristics of attachment and growth of Thiobacillus caldus on sulphide minerals: a chemotactic response to sulphur minerals?

To further our understanding of the ecological role of sulphur-oxidizing microorganisms in the generation of acid mine drainage (AMD), growth and attachment of the chemoautotrophic sulphur-oxidizing bacterium, Thiobacillus caldus, on the sulphide minerals pyrite, marcasite and arsenopyrite was studied. Growth curves were estimated based on total cells detected in the system (in suspension and attached to mineral surfaces). In general, higher cell numbers were detected on surfaces than in suspension. Fluorescent in situ hybridizations to cells on surfaces at mid-log growth confirmed that cells on surfaces were metabolically active. Total cell (both surface and solution phase) generation times on pyrite and marcasite (both FeS2) were calculated to be approximately equals 7 and 6 h respectively. When grown on pyrite (not marcasite), the number of T. caldus cells in the solution phase decreased, while the total number of cells (both surface and solution) increased. Additionally, marcasite supported about three times more total cells (approximately equals 3 x 10(9)) than pyrite (approximately equals 8 x 10(8)). This may be attributed to the dissolution rate of marcasite, which is twice that of pyrite. Epifluorescent and scanning electron microscopy (SEM) were used to analyse the cell orientation on surfaces. Results of Fourier transform analysis of fluorescent images confirmed that attachment to all three sulphides occurred in an oriented manner. Results from high-resolution SEM imaging showed that cell orientation coincides with dissolution pit edges and secondary sulphur minerals that develop during dissolution. Preferential colonization of surfaces relative to solution and oriented cell attachment on these sulphide surfaces suggest that T. caldus may chemotactically select the optimal site for chemoautotrophic growth on sulphur (i.e. the mineral surface).

An archaeal iron-oxidizing extreme acidophile important in acid mine drainage

A new species of Archaea grows at pH approximately 0.5 and approximately 40 degrees C in slime streamers and attached to pyrite surfaces at a sulfide ore body, Iron Mountain, California. This iron-oxidizing Archaeon is capable of growth at pH 0. This species represents a dominant prokaryote in the environment studied (slimes and sediments) and constituted up to 85% of the microbial community when solution concentrations were high (conductivity of 100 to 160 millisiemens per centimeter). The presence of this and other closely related Thermoplasmales suggests that these acidophiles are important contributors to acid mine drainage and may substantially impact iron and sulfur cycles.

Seasonal variations in microbial populations and environmental conditions in an extreme acid mine drainage environment

Microbial populations, their distributions, and their aquatic environments were studied over a year (1997) at an acid mine drainage (AMD) site at Iron Mountain, Calif. Populations were quantified by fluorescence in situ hybridizations with group-specific probes. Probes were used for the domains Eucarya, Bacteria, and Archaea and the two species most widely studied and implicated for their role in AMD production, Thiobacillus ferrooxidans and Leptospirillum ferrooxidans. Results show that microbial populations, in relative proportions and absolute numbers, vary spatially and seasonally and correlate with geochemical and physical conditions (pH, temperature, conductivity, and rainfall). Bacterial populations were in the highest proportion (>95%) in January. Conversely, archaeal populations were in the highest proportion in July and September ( approximately 50%) and were virtually absent in the winter. Bacterial and archaeal populations correlated with conductivity and rainfall. High concentrations of dissolved solids, as reflected by high conductivity values (up to 125 mS/cm), occurred in the summer and correlated with high archaeal populations and proportionally lower bacterial populations. Eukaryotes were not detected in January, when total microbial cell numbers were lowest (<10(5) cells/ml), but eukaryotes increased at low-pH sites ( approximately 0.5) during the remainder of the year. This correlated with decreasing water temperatures (50 to 30 degrees C; January to November) and increasing numbers of prokaryotes (10(8) to 10(9) cells/ml). T. ferrooxidans was in highest abundance (>30%) at moderate pHs and temperatures ( approximately 2.5 and 20 degrees C) in sites that were peripheral to primary acid-generating sites and lowest (0 to 5%) at low-pH sites (pH approximately 0.5) that were in contact with the ore body. L. ferrooxidans was more widely distributed with respect to geochemical conditions (pH = 0 to 3; 20 to 50 degrees C) but was more abundant at higher temperatures and lower pHs ( approximately 40 degrees C; pH approximately 0.5) than T. ferrooxidans.

Biological impact on mineral dissolution: application of the lichen model to understanding mineral weathering in the rhizosphere

Microorganisms modify rates and mechanisms of chemical and physical weathering and clay growth, thus playing fundamental roles in soil and sediment formation. Because processes in soils are inherently complex and difficult to study, we employ a model based on the lichen-mineral system to identify the fundamental interactions. Fixed carbon released by the photosynthetic symbiont stimulates growth of fungi and other microorganisms. These microorganisms directly or indirectly induce mineral disaggregation, hydration, dissolution, and secondary mineral formation. Model polysaccharides were used to investigate direct mediation of mineral surface reactions by extracellular polymers. Polysaccharides can suppress or enhance rates of chemical weathering by up to three orders of magnitude, depending on the pH, mineral surface structure and composition, and organic functional groups. Mg, Mn, Fe, Al, and Si are redistributed into clays that strongly adsorb ions. Microbes contribute to dissolution of insoluble secondary phosphates, possibly via release of organic acids. These reactions significantly impact soil fertility. Below fungi-mineral interfaces, mineral surfaces are exposed to dissolved metabolic byproducts. Through this indirect process, microorganisms can accelerate mineral dissolution, leading to enhanced porosity and permeability and colonization by microbial communities.

Imperfect oriented attachment: dislocation generation in defect-free nanocrystals

Dislocations are common defects in solids, yet all crystals begin as dislocation-free nuclei. The mechanisms by which dislocations form during early growth are poorly understood. When nanocrystalline materials grow by oriented attachment at crystallographically specific surfaces and there is a small misorientation at the interface, dislocations result. Spiral growth at two or more closely spaced screw dislocations provides a mechanism for generating complex polytypic and polymorphic structures. These results are of fundamental importance to understanding crystal growth.

Distribution of thiobacillus ferrooxidans and leptospirillum ferrooxidans: implications for generation of acid mine drainage

Although Thiobacillus ferrooxidans and Leptospirillum ferrooxidans are widely considered to be the microorganisms that control the rate of generation of acid mine drainage, little is known about their natural distribution and abundance. Fluorescence in situ hybridization studies showed that at Iron Mountain, California, T. ferrooxidans occurs in peripheral slime-based communities (at pH over 1.3 and temperature under 30 degreesC) but not in important subsurface acid-forming environments (pH 0.3 to 0.7, temperature 30 degrees to 50 degreesC). Leptospirillum ferrooxidans is abundant in slimes and as a planktonic organism in environments with lower pH. Thiobacillus ferrooxidans affects the precipitation of ferric iron solids but plays a limited role in acid generation, and neither species controls direct catalysis at low pH at this site.

High-Resolution and Analytical Transmission Electron Microscopy of Mineral Disorder and Reactions

Crystal defects and chemical reactions occurring at scales beyond the resolution of light microscopes have major effects on the chemical and physical properties of rocks and minerals. High-resolution imaging, diffraction, and chemical analysis in the transmission electron microscope have become important methods for exploring mineral defect structures and reaction mechanisms and for studying the distribution of phases resulting from reactions. These techniques have shown that structural disorder is common in some rock-forming minerals but rare in others. They have also established mechanisms by which many reactions occur at the atomic cluster scale. These data thus provide an atomistic basis for understanding the kinetics of geological reactions. Furthermore, apparent major-element, minor-element, and trace-element chemistry of minerals can be influenced by submicroscopic inclusions or intergrowths, which commonly form as products of solid-state reactions.