Microbial acceleration of aerobic pyrite oxidation at circumneutral pH

Pyrite (FeS₂) is the most abundant sulfide mineral on Earth and represents a significant reservoir of reduced iron and sulfur both today and in the geologic past. In modern environments, oxidative transformations of pyrite and other metal sulfides play a key role in terrestrial element partitioning with broad impacts to contaminant mobility and the formation of acid mine drainage systems. Although the role of aerobic micro‐organisms in pyrite oxidation under acidic‐pH conditions is well known, to date there is very little known about the capacity for aerobic micro‐organisms to oxidize pyrite at circumneutral pH. Here, we describe two enrichment cultures, obtained from pyrite‐bearing subsurface sediments, that were capable of sustained cell growth linked to pyrite oxidation and sulfate generation at neutral pH. The cultures were dominated by two Rhizobiales species (Bradyrhizobium sp. and Mesorhizobium sp.) and a Ralstonia species. Shotgun metagenomic sequencing and genome reconstruction indicated the presence of Fe and S oxidation pathways in these organisms, and the presence of a complete Calvin–Benson–Bassham CO₂ fixation system in the Bradyrhizobium sp. Oxidation of pyrite resulted in thin (30–50 nm) coatings of amorphous Fe(III) oxide on the pyrite surface, with no other secondary Fe or S phases detected by electron microscopy or X‐ray absorption spectroscopy. Rates of microbial pyrite oxidation were approximately one order of magnitude higher than abiotic rates. These results demonstrate the ability of aerobic microbial activity to accelerate pyrite oxidation and expand the potential contribution of micro‐organisms to continental sulfide mineral weathering around the time of the Great Oxidation Event to include neutral‐pH environments. In addition, our findings have direct implications for the geochemistry of modern sedimentary environments, including stimulation of the early stages of acid mine drainage formation and mobilization of pyrite‐associated metals.     

Silicate Dissolution in Las Pailas Thermal Field: Implications for Microbial Weathering in Acidic Volcanic Hydrothermal Spring Systems

A longitudinal field microcosm study was conducted in the Las Pailas hot spring system, located on the SW flank of Rincon de la Vieja, Costa Rica, in order to investigate initial microbial attachment and colonization, as well as chemical (abiotic) and biological silicate weathering under hydrothermal conditions. Solution chemistry was pH = 2.42–3.96, T = 43–89.3°C, Si = 4.45–8.19 mmol L^?1, Fe = 1.50–6.95 mmol L^?1and PO^3? ₄ = below detection limits-4.9 μmol L^?1. Microcosms consisted of washed, sonicated primary silicate samples in polycarbonate vessels. The vessels were enclosed either by mesh to observe water/rock/microbial interactions or by 0.2–0.45 μm filters to observe water/rock interactions. Microcosms were incubated for periods of 6 h, 24 h, or 2 mo, fixed in the field, then analyzed in the laboratory. Scanning electron microscopy (SEM) analysis revealed that microbial attachment to mineral samples occurred in as little as 6 h. Microbial colonization and the development of minor etch pits associated with microorganisms occurred within 24 h. The most significant differences in chemical vs. biological weathering were observed after 2 mo. SEM analysis of these incubated surfaces showed that volumetric losses to mineral samples were more than one order of magnitude greater for samples that had been colonized by microorganisms and thus weathered biologically. With time, preferential colonization of anorthoclase mineral samples with Fe-oxides and apatite inclusions occurred. Subsequent weathering, therefore, may be a metabolic strategy by microorganisms to access mineral-bound PO^3? ₄, which is otherwise scarce in solution. Results from this study suggest that microorganisms may play a significant role in weathering in some hydrothermal systems.     

Further Readings in Geomicrobiology

Microbial biofilms preferentially colonized pyrite surfaces of black shale incubated in groundwater in the Newark Basin (northeastern United States) for 1 month. SEM observation revealed the co-occurrence of bacteria-shaped pits and secondary iron minerals on pyrite, which indicate biological involvement in pyrite weathering and secondary solid formation. Of the 24 16S rDNA sequences obtained from bacterial communities on pyrite, arsenopyrite and quartz sand, 22 belonged to the phylum proteobacteria, including 5 identified as β or ?-proteobacteria capable of oxidizing iron or sulfur, 16 identified as members of the Fe(III)-reducing Geobacteraceae in the δ-proteobacteria and one identified as the Fe(III)-reducing Ferribacterium. Results indicate that microbes play an essential role in the oxidation of iron sulfides (via direct contact and indirect pathways) and the reduction of iron oxides in pyrite-bearing substrata of a slightly acidic black shale aquifer.     

不同风化时间碳酸岩表面古菌群落结构与功能特征

【背景】古菌群落是碳酸岩表面微生物群落的重要成员,也是碳酸岩表面生物演替的先锋生物,能够促进碳酸岩风化和加快土壤形成,在生物地球化学循环中起重要作用。【目的】揭示在不同风化时间碳酸岩表面风化残积物中的古菌群落结构及生态功能。方法】采集19-213年风化时间段废弃碳酸岩墓碑表面风化残积物样品(n=18),基于宏基因组测序技术分析其古菌群落结构与功能特征。【结果】门水平上,优势门有广古菌门(Euryarchaeota),随后为奇古菌门(Thaumarchaeota)、未鉴定古菌门(unclassified Archaea)、深古菌门(Bathyarchaeota)和泉古菌门(Crenarchaeota);属水平上,优势属主要由甲烷八叠球菌属(Methanosarcina)、甲烷丝状菌属(Methanothrix)、Methanoperedens、氨氧化古菌属(Nitrosocosmicus)、亚硝化球菌属(Nitrososphaera)及其他未鉴定属组成;C/N、C/P、N/P是显著影响碳酸岩表面古菌群落的主要环境因子。进一步分析发现,碳酸岩表面古菌群落功能丰富,其中新陈代谢(metabo...     

The effect of bacteria and fungi on chemical weathering and chemical denudation fluxes in pine growth experiments

Vascular plants and associated microbial communities affect the nutrient resources of terrestrial ecosystems by impacting chemical weathering that transfers elements from primary minerals to other ecosystem pools, and chemical denudation that transports weathered elements out of the system in solution. We performed a year-long replicated flow-through column growth experiment to isolate the effects of vascular plants, ectomycorrhiza-forming fungi and associated bacteria on chemical weathering and chemical denudation. The study focused on Ca²⁺, K⁺ and Mg²⁺, for which the sole sources were biotite and anorthite mixed into silica sand. Concentrations of the cations were measured in input and output solutions, and three times during the year in plant biomass and on exchangeable cation sites of the growth medium. Weathering and denudation fluxes were estimated by mass balance, and mineral surface changes, biofilm and microbial attachments to surfaces were investigated with scanning electron microscopy. Both bacteria and fungi increased weathering fluxes compared to abiotic controls. Without a host plant denudation rates were as large as weathering rates i.e. the weathering to denudation ratio was about one. Based on whole year fluxes, ectomycorrhizal seedlings produced the greatest weathering to denudation ratios (1.5). Non-ectomycorrhizal seedlings also showed a high ratio of 1.3. Both ectomycorrhizal hyphal networks and root hairs of non-ectomycorrhizal trees, embedded in biofilm (microorganisms surrounded by extracellular polymers), transferred nutrients to the host while drainage losses were minimized. These results suggest that biofilms localize both weathering and plant nutrient uptake, isolating the root-hypha-mineral interface from bulk soil solution.     

Sedimentary pyrite sulfur isotope compositions preserve signatures of the surface microbial mat environment in sediments underlying low-oxygen cyanobacterial mats

The sedimentary pyrite sulfur isotope (δ³⁴S) record is an archive of ancient microbial sulfur cycling and environmental conditions. Interpretations of pyrite δ³⁴S signatures in sediments deposited in microbial mat ecosystems are based on studies of modern microbial mat porewater sulfide δ³⁴S geochemistry. Pyrite δ³⁴S values often capture δ³⁴S signatures of porewater sulfide at the location of pyrite formation. However, microbial mats are dynamic environments in which biogeochemical cycling shifts vertically on diurnal cycles. Therefore, there is a need to study how the location of pyrite formation impacts pyrite δ³⁴S patterns in these dynamic systems. Here, we present diurnal porewater sulfide δ³⁴S trends and δ³⁴S values of pyrite and iron monosulfides from Middle Island Sinkhole, Lake Huron. The sediment–water interface of this sinkhole hosts a low-oxygen cyanobacterial mat ecosystem, which serves as a useful location to explore preservation of sedimentary pyrite δ³⁴S signatures in early Earth environments. Porewater sulfide δ³⁴S values vary by up to ~25‰ throughout the day due to light-driven changes in surface microbial community activity that propagate downwards, affecting porewater geochemistry as deep as 7.5 cm in the sediment. Progressive consumption of the sulfate reservoir drives δ³⁴S variability, instead of variations in average cell-specific sulfate reduction rates and/or sulfide oxidation at different depths in the sediment. The δ³⁴S values of pyrite are similar to porewater sulfide δ³⁴S values near the mat surface. We suggest that oxidative sulfur cycling and other microbial activity promote pyrite formation in and immediately adjacent to the microbial mat and that iron geochemistry limits further pyrite formation with depth in the sediment. These results imply that primary δ³⁴S signatures of pyrite deposited in organic-rich, iron-poor microbial mat environments capture information about microbial sulfur cycling and environmental conditions at the mat surface and are only minimally affected by deeper sedimentary processes during early diagenesis.     

Comparative study of weathering signatures in felsic igneous rocks of Hong Kong

Abstract

Mineralogical, petrographical and geochemical characteristics of two weathered profiles, derived from rhyolitic tuff and granitic rocks under humid conditions, were studied by atomic absorption spectrometry, X-ray fluorescence spectrometry, inductively coupled plasma-mass spectrometry, and X-ray diffractometry. The granitic profile is derived from medium-grained, equigranular monzogranitic parent rocks and typically contains corestones, whereas the pyroclastic profile is derived from rhyolitic crystal-vitric tuffs, which were subjected to deuteric alteration prior to weathering. The two parent rocks contain similar primary mineral constituents and display similar sequential changes in response to weathering at mineral scale. However, samples of the granitic profile reveal more pronounced intergranular and transgranular microcracks and wider grain boundaries compared with samples of the same weathering grade from the pyroclastic profile. Sesquioxide networks and veins are more common in the pyroclastic profile than in the granitic profile.

Special emphasis is given to the type, abundance and distribution of clay minerals within the weathered profiles. Kaolinite, halloysite, illite and interstratified smectite are ubiquitous clay-size minerals of both profiles. However, the abundance of clay minerals varies significantly within each profile as well as between profiles. The granitic profile is dominated by halloysite regardless of the degree of weathering, whereas halloysite is the dominant clay mineral only in moderately to highly decomposed samples of the pyroclastic profile. The relative abundance of illite in the granitic profile is rather low (less than 10%) and more stable than the profile compared to the pyroclastic profile where illite is the dominant clay mineral in fresh to moderately decomposed samples. In general, as the intensity of weathering increases, the relative abundance ratios of halloysite to kaolinite and illite to kaolin decrease.

Parent rock normalized chemical variation diagrams reveal that as the intensity of weathering increases, Ca, Na, K, Rb and Sr contents decrease, whereas Al, Mg, Mn, Ti, Cu, Cr, Ni, Ba, Sc and LOI contents increase. Although these variations can easily be explained by decomposition of feldspar grains and formation of sesquioxides and clay minerals, overall chemical trends are not sufficiently systematic to allow prediction of theweathering degree of a given sample based solely on its chemical composition. In general, the granitic profile has been developed under better-drained and more hydrous conditions compared to the pyroclastic profile. Microenvironmental conditions, which are significantly different between the two profiles, ultimately control the type and abundance of clay minerals and the distribution of sesquioxides, and thus govern the level of microfabric heterogeneity in weathered profiles.     

河南卢氏和江西宜春两处锂矿山地表微生物群落分布特征差异及成因分析

[目的] 揭示地表锂矿石表面和风化产物中细菌群落多样性特征。[方法] 针对细菌16S rRNA片段扩增进行高通量测序,分析不同锂矿石表面及其风化产物中细菌群落组成、多样性及功能属性等信息。[结果] 河南卢氏南阳山伟晶岩型锂矿石和江西宜春花岗岩型锂矿石表面及其风化产物的细菌群落多样性有差异。南阳山伟晶岩矿石与其风化产物、宜春花岗岩矿石表面和风化产物（NK-1、NK-1F、YK-1、YK-1F、YK-2、YK-2F、YK-3）的OTUs分别是1010、540、835、828、1117、974和604,其差异与不同的矿物组成显著关联。两矿山均有其优势微生物,在门水平上,两矿山均以放线菌门（Actinobacteria）、变形菌门（Proteobacteria）为优势菌门。同时两矿区微生物群落组成具有显著差异性（P<0.05）,不同地理位置风化产物样本之间差异尤为显著（P<0.001）;在属水平上,NK-1中相对丰度大于5%的属为鞘氨醇单胞菌属（Sphingomonas）、马赛菌属（Massilia）;NK-1F为类芽孢杆菌属（Paenibacillus）、杆状细菌属（Bacillus）、马赛菌属（Massilia）;YK-1F为芽球菌属（Blastococcus）、念珠菌固体杆菌属（Candidatus-Solibacter）、Noviherbaspirillum属、伯克霍尔德氏菌属（Burkholderia-Caballeronia-Paraburkholderia）,YK-2为unidentified-Chloroplast属,YK-2F为北里孢菌属（Kitasatospora）,YK-3为1174-901-12属、甲基杆菌属（Methylobacterium）。不同地理位置的矿石及其风化物样本的功能注释均涉及代谢、遗传信息处理、环境信息处理等6个代谢通路。[结论] 16S rRNA高通量测序揭示不同地区锂矿石及其风化产物的细菌多样性存在差异,各具优势类群,样本间菌落组成、多样性及功能属性的差异与锂矿石化学组成、风化程度和地理分布密切相关。这项研究揭示了优势微生物类群的元素地球化学功能与含锂矿物地表风化的潜在联系,可为微生物生态分布研究及相关微生物资源开发提供新数据。     

In situ S‐isotope compositions of sulfate and sulfide from the 3.2 Ga Moodies Group,South Africa: A record of oxidative sulfur cycling

Sulfate minerals are rare in the Archean rock record and largely restricted to the occurrence of barite (BaSO₄). The origin of this barite remains controversially debated. The mass‐independent fractionation of sulfur isotopes in these and other Archean sedimentary rocks suggests that photolysis of volcanic aerosols in an oxygen‐poor atmosphere played an important role in their formation. Here, we report on the multiple sulfur isotopic composition of sedimentary anhydrite in the ca. 3.22 Ga Moodies Group of the Barberton Greenstone Belt, southern Africa. Anhydrite occurs, together with barite and pyrite, in regionally traceable beds that formed in fluvial settings. Variable abundances of barite versus anhydrite reflect changes in sulfate enrichment by evaporitic concentration across orders of magnitude in an arid, nearshore terrestrial environment, periodically replenished by influxes of seawater. The multiple S‐isotope compositions of anhydrite and pyrite are consistent with microbial sulfate reduction. S‐isotope signatures in barite suggest an additional oxidative sulfate source probably derived from continental weathering of sulfide possibly enhanced by microbial sulfur oxidation. Although depositional environments of Moodies sulfate minerals differ strongly from marine barite deposits, their sulfur isotopic composition is similar and most likely reflects a primary isotopic signature. The data indicate that a constant input of small portions of oxidized sulfur from the continents into the ocean may have contributed to the observed long‐term increase in Δ³³S_sulfate values through the Paleoarchean.     

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 ~0.5 to ~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 (~43°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.     

Sebastiano Genovese: In Memoriam

Abstract

Laboratory simulations have helped resolve several problems concerning the role of bacteria in producing acidic drainage from active and abandoned coal mines. It is well established that the bacterium Thiobacillus ferrooxidans oxidizes pyrite in synthetic liquid media and in flooded or agitated experimental simulations of coal mine environments. However, many geologists remain skeptical regarding the role of T. ferrooxidans in producing acidity below a near‐surface belt of soil water. We have demonstrated that T. ferrooxidans is capable of colonizing and acidifying a near‐neutral pH environment of crushed coal or overburden, without prior establishment of a pH‐dependent succession of bacteria. We have suggested that T. ferrooxidans may accomplish this by direct oxidation of pyrite. We have also shown that T. ferrooxidans catalyzes pyrite oxidation in the intermediate belt of the zone of aeration, although only for a limited period of time after rainfall infiltration. T. ferrooxidans was not found to be significant in the simulated zone of groundwater saturation.     

Temporal and spatial development of soil solution chemistry and element budgets in different mine soils of the Lusatian lignite mining area

Lignite and pyrite contents in the dump materials of the Lusatian opencast mining district in East Germany result in high acidification and salinization potentials. These extreme conditions require considerable amounts of alkaline materials like ash or lime to enable recultivation and revegetation. Investigations at chronosequence sites on different mining substrates show characteristic developments of the soil solution chemistry. Processes like weathering of primary and formation of secondary mineral phases, acid production and buffering, and their impacts on both the solid and the liquid soil phase result in high temporal and spatial dynamics especially in the initial phase of soil and ecosystem development. To study these processes we continuously collected soil solutions from different soil depths at seven sites with two representative soil substrates. All sites were afforested with pine and cover stand ages from 1 to 60 yr. The results show that actual pyrite oxidation occurs at the youngest sites on lignite and pyrite containing substrates leading to extremely low pH values and high Feⁿ⁺ and SO₄ ²- concentrations. The considerable acid production causes weathering of aluminium silicates resulting in high Alⁿ⁺ concentrations. Ca²⁺ concentrations are unexpectedly high even at low pH showing no correlation to amelioration amounts or depths. Therefore it seems most probable that these mining substrates contain geogenic Ca sources. The transport of dissolved weathering products is limited due to low leaching rates enabling formation of secondary phases which control the actual composition of the soil solution. Depth gradients of the soil solution composition at the chronosequence sites point to a gradual transport and leaching of these secondary phases from the soil profiles. Soil solution composition and dynamics at lignite and pyrite free sites show completely different patterns and have a higher potential for successful sustainable recultivation. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

An RNA-Sequencing Study of the Genes and Metabolic Pathways Involved in Aspergillus niger Weathering of Potassium Feldspar

Microbial transformation of potassium feldspar to produce organic composite potassium fertilizer is recognized to be an important method of effective use of the huge reserves of low grade K⁺-bearing rock in China. The mechanism underlying microbial weathering of silicate minerals is still unclear, and this is an obstacle to practical methods of application. To thoroughly understand the molecular mechanism responsible for the weathering of potassium feldspar by Aspergillus niger at a molecular level, high-throughput RNA-sequencing (RNA-seq) and treatment with different potassium sources (cultured in Czapek medium with soluble K⁺ or potassium feldspar) were used to investigate the differentially expressed genes of A. niger associated with potassium feldspar weathering and the related metabolic pathways. A series of differentially expressed genes related to the synthesis and transportation of organic acids, polysaccharides, and proteins (enzymes) were found to be closely associated with the K⁺ released from minerals through bioinformatic analysis. In addition, 12 genes that showed apparent expression differences by RNA-seq analysis and are relevant to organic acid synthesis, protein modification, maintenance of cellular homeostasis, and material transportation, were selected to be further verified using RT-qPCR. Compared to the fungal samples cultured with soluble K⁺, those with potassium feldspar have certain genes that are more up-regulated, such as the genes for Na⁺,K⁺-ATPase (447.6 multiples), cystathionine beta-synthase (5.6 multiples), cysteine synthase (9 multiples), and glutathione synthase (3.5 multiples). The analysis indicates that A. niger weathering of potassium feldspar is due to the synergistic effect of many factors including the up-regulation of certain genes and activation of related metabolite pathways. The research improves our understanding of the mechanisms of microbial weathering of silicate minerals.     

Accelerated weathering and biodegradation of E-glass polyester composites

Successful material performance of composites depends on the environmental conditions to which they are exposed. Biological factors in aquatic environments may accelerate material deterioration. Simultaneously, leached constituents can adversely affect the surrounding ecosystem. An accelerated weathering was used to demonstrate the ease of coupon biodeterioration. In 3 months, 21 mg l⁻¹ of organics were leached, aquatic bacteria numbers increased by 43%, and biofilm growth was accelerated. Degradability of leached compounds was tested in experiments with water collected from the accelerated weathered coupons and a synthetic leachate. The first experiment verified isophthalaldehyde as a polyester biodegradation byproduct. Although the rate of biodegradation was twice that of the abiotic system, microbial numbers had reduced from 5.0×10⁷ to 5.4×10⁴ CFU l⁻¹. Synthetic resin experiments showed that the bacteria were able to use the resin as a carbon source. However, compound toxicity prevented exponential growth of the bacteria.     

Karst development and sulfur deposit formation in the Ordos Basin: The role of bacterial sulfate reduction

Bacterial sulfate reduction is significant for the karst development and pyrite formation within the Ordovician weathering crust in the Ordos Basin of China. Bacterial communities were studied to determine their potential geomicrobiological functioning by constructing 16S rRNA clone library for in situ samples. The results showed that 147 positive clones sequenced were divided into 23 operational taxonomic units (OTUs), 8 OTUs accouting for 80% of all the selected clones belonged to the genus Desulfosporosinus. Bacterial sulfate reduction has been demonstrated to take place in the Ordovician by the classical hydrogeological information together with the stable sulfur isotope analysis from both the pyrite in the weathering crust and the products of the laboratory experiments on the dissolution of sulfate rock. The H₂S produced by bacterial sulfate reduction combined with iron to form pyrite, resulting in the development of hypogenic karst in the weathering crust. This process provided a reasonable interpretation for karst development in the vicinity of sulfur deposits in the Ordos Basin.     

Actinobacteria—An Ancient Phylum Active in Volcanic Rock Weathering

A molecular biological analysis of Icelandic volcanic rocks of different compositions and glassiness revealed the presence of Actinobacteria as an abundant phylum. In outcrops of basaltic glass they were the dominant bacterial phylum. A diversity of Actinobacteria were cultured from the rocks on rock-agar plates showing that they are capable of growing on rock-derived nutrient sources and that many of the taxa identified by molecular methods are viable, potentially active members of the community. Laboratory batch-culture experiments using a Streptomyces isolate showed that it was capable of enhancing the release of major elements from volcanic rocks, including weathered basaltic glass, crystalline basalt and komatiite, when provided with a carbon source. Actinobacteria of a variety of other sub-orders were also capable of enhancing volcanic rock weathering, measured as Si release. However, most strains did not significantly increase the weathering of the silica-rich rock, obsidian. These data show that Actinobacteria can contribute to volcanic rock weathering and, therefore, the carbonate-silicate cycle. Given their ancient lineage, it is likely they have played a role in rock weathering for over two billion years.     

Weathering of calcite,pyrite, and sulfur by Thermothrix thiopara in a thermal spring

The mineral weathering capabilities of Thermothrix thiopara were investigated by scanning electron microscopy and energy dispersive X‐ray analysis. Thermothrix thiopara is an extremely thermophilic, sulfur‐oxidizing bacterium that grows in a thermal spring whose principal minerals are calcium carbonate, pyrite, and sulfur. Crystals of these minerals were incubated in situ for periods up to eight days, removed, and examined. Results indicated that T. thiopara is partially responsible for weathering calcium carbonate by the production of sulfuric acid, thereby contributing to the formation of a porous tufa mound. Examination of ultravioletirradiated control crystals indicated that the sulfuric acid produced by T. thiopara caused solubilization of calcium carbonate even in the absence of direct bacterial colonization. Pyrite and sulfur were not visibly weathered, but instead were coated with calcium carbonate precipitate. During eight days incubation, growth forms of T. thiopara colonizing the minerals progressed from unicells to filaments to nets of filaments. Bacteria other than T. thiopara appeared after eight days, indicating an increased diversity.     

The removal of pyritic sulphur from coal by Leptospirillum-like bacteria

Summary The microbial oxidation of pyritic sulphur was studied in a 4.5-l airlift fermentor at pH 1.5 and 100 g/l pulp density. By microbial leaching with Leptospirillum-like bacteria 85% of the pyritic sulphur was removed within 40 days; 30% of the removed pyrite was oxidized to elemental sulphur, the rest being transformed to soluble sulphate. Accumulation of elemental sulphur could be avoided by using a mixed culture of Leptospirillum-like bacteria and Thiobacillus ferrooxidans. Apart from oxidation of elemental sulphur neither the pure nor the mixed culture showed a significant difference as to removal of pyrite.     

In situ trace metal analysis of Neoarchaean – Ordovician shallow‐marine microbial‐carbonate‐hosted pyrites

Pre‐Cambrian atmospheric and oceanic redox evolutions are expressed in the inventory of redox‐sensitive trace metals in marine sedimentary rocks. Most of the currently available information was derived from deep‐water sedimentary rocks (black shale/banded iron formation). Many of the studied trace metals (e.g. Mo, U, Ni and Co) are sensitive to the composition of the exposed land surface and prevailing weathering style, and their oceanic inventory ultimately depends on the terrestrial flux. The validity of claims for increased/decreased terrestrial fluxes has remained untested as far as the shallow‐marine environment is concerned. Here, the first systematic study of trace metal inventories of the shallow‐marine environment by analysis of microbial carbonate‐hosted pyrite, from ca. 2.65–0.52 Ga, is presented. A petrographic survey revealed a first‐order difference in preservation of early diagenetic pyrite. Microbial carbonates formed before the 2.4 Ga great oxygenation event (GOE) are much richer in pyrite and contain pyrite grains of greater morphological variability but lesser chemical substitution than samples deposited after the GOE. This disparity in pyrite abundance and morphology is mirrored by the qualitative degree of preservation of organic matter (largely as kerogen). Thus, it seems that in microbial carbonates, pyrite formation and preservation were related to presence and preservation of organic C. Several redox‐sensitive trace metals show interpretable temporal trends supporting earlier proposals derived from deep‐water sedimentary rocks. Most notably, the shallow‐water pyrite confirms a rise in the oceanic Mo inventory across the pre‐Cambrian–Cambrian boundary, implying the establishment of efficient deep‐ocean ventilation. The carbonate‐hosted pyrite also confirms the Neoarchaean and early Palaeoproterozoic ocean had higher Ni concentration, which can now more firmly be attributed to a greater proportion of magnesian volcanic rock on land rather than a stronger hydrothermal flux of Ni. Additionally, systematic trends are reported for Co, As, and Zn, relating to terrestrial flux and oceanic productivity.     

Habitat and sediment preferences ofAxarus festivus larvae

During fall draw-down of a reservoir in northeast Kansas it was observed that larvae ofAxarus festivus were restricted to highly weathered Pennsylvanian Shale outcrops and surrounding coarse sediments with high-clay content derived from erosion of the shale outcroppings. Larvae constructed burrows into the outcrops and eroded coarse sediments, which they used to filter feed by setting up currents through the burrows. Burrows were widely distributed over the outcrops, with average densities ranging from 372–2,351 burrows m^–2. However, closer inspection revealed that burrows were more common at apices of individual shale strata, where weathering of the outcrop was most advanced. Here burrows were more uniformly distributed and densities ranged to 4,166 burrows m^–2. 73% of burrows contained larvae. Burrows were generally U-shaped, and averaged 1.8 mm in diameter and 42 mm in total length. Laboratory experiments revealed that 4th instar larvae removed from burrows could construct new burrows in weathered shale, but preferentially used old empty burrows if available. When given choices among alternative sediment combinations of sandvs. finely-ground shale, sandvs. coarsely-ground shale, and finely-ground shalevs. coarsely-ground shale, larvae exhibited statistically significant preferences for the finely-ground shales (P<0.001), coarsely-ground shales (P<0.001), and coarsely-ground shales (P<0.01), respectively. It is concluded that larvae (1) actively select shale or high-clay content sediments, (2) can differentiate among sediments with differing physical properties and (3) exhibit behavioral choices for sediment types that guide them toward shale outcrops.