Oxide Mats Research Articles

Microbial community response to hydrocarbon exposure in iron oxide mats: an environmental study.

Hydrocarbon pollution is a widespread issue in both groundwater and surface-water systems; however, research on remediation at the interface of these two systems is limited. This interface is the oxic-anoxic boundary, where hydrocarbon pollutant from contaminated groundwaters flows into surface waters and iron mats are formed by microaerophilic iron-oxidizing bacteria. Iron mats are highly chemically adsorptive and host a diverse community of microbes. To elucidate the effect of hydrocarbon exposure on iron mat geochemistry and microbial community structure and function, we sampled iron mats both upstream and downstream from a leaking underground storage tank. Hydrocarbon-exposed iron mats had significantly higher concentrations of oxidized iron and significantly lower dissolved organic carbon and total dissolved phosphate than unexposed iron mats. A strong negative correlation between dissolved phosphate and benzene was observed in the hydrocarbon-exposed iron mats and water samples. There were positive correlations between iron and other hydrocarbons with benzene in the hydrocarbon-exposed iron mats, which was unique from water samples. The hydrocarbon-exposed iron mats represented two types, flocculent and seep, which had significantly different concentrations of iron, hydrocarbons, and phosphate, indicating that iron mat is also an important context in studies of freshwater mats. Using constrained ordination, we found the best predictors for community structure to be dissolved oxygen, pH, and benzene. Alpha diversity and evenness were significantly lower in hydrocarbon-exposed iron mats than unexposed mats. Using 16S rDNA amplicon sequences, we found evidence of three putative nitrate-reducing iron-oxidizing taxa in microaerophile-dominated iron mats (Azospira, Paracoccus, and Thermomonas). 16S rDNA amplicons also indicated the presence of taxa that are associated with hydrocarbon degradation. Benzene remediation-associated genes were found using metagenomic analysis both in exposed and unexposed iron mats. Furthermore, the results indicated that season (summer vs. spring) exacerbates the negative effect of hydrocarbon exposure on community diversity and evenness and led to the increased abundance of numerous OTUs. This study represents the first of its kind to attempt to understand how contaminant exposure, specifically hydrocarbons, influences the geochemistry and microbial community of freshwater iron mats and further develops our understanding of hydrocarbon remediation at the land-water interface.

Preparation, Properties and Water Dissolution Behavior of Polyethylene Oxide Mats Prepared by Solution Blow Spinning.

The relationship between processing conditions, structure and morphology are key issues to understanding the final properties of materials. For instance, in the case of polymers to be used as scaffolds in tissue engineering, wound dressings and membranes, morphology tuning is essential to control mechanical and wettability behaviors. In this work, the relationship between the processing conditions of the solution blow spinning process (SBS) used to prepare nonwoven mats of polyethylene oxide (PEO), and the structure and morphology of the resulting materials are studied systematically, to account for the thermal and mechanical behaviors and dissolution in water. After finding the optimal SBS processing conditions (air pressure, feed rate, working distance and polymer concentration), the effect of the solvent composition has been considered. The structure and morphology of the blow spun fibers are studied as well as their thermal, mechanical behaviors and dissolution in water. We demonstrate that the morphology of the fibers (size and porosity) changes with the solvent composition, which is reflected in different thermal and mechanical responses and in the dissolution rates of the materials in water.

Needleless electrospun carboxymethyl cellulose/polyethylene oxide mats with medicinal plant extracts for advanced wound care applications

Electrospinning as method for fabrication of wound dressing materials with included medical plant extracts for wound treatment has lately gained increasing attention. However, the transfer of nanofiber fabrication with included plant extracts from the research to the pilot and industrial scale production, using needleless electrospinning is a vital area of research, which could enable its large-scale commercial exploitation. Carboxymethyl cellulose (CMC) is a cheap, water soluble biopolymer, and in blends with the spinning agent polyethylene oxide (PEO) it is a suitable polymer for a large-scale nanofiber production. Thus, this study addresses the needleless electrospinning of CMC/PEO/plant extract blend aqueous solutions in order to fabricate cellulose based wound dressing material, suitable for treatment of acute wounds. The influence of plant extracts on the morphology of the electrospun mats was further evaluated. The antioxidant and antibacterial properties of the as-prepared electrospun mats were determined, where special attention was devoted to the stability/degradation study of phenolic compounds in plant extracts during the electrospinning process. This research was complemented by the release study and cell viability testing with results indicating a promising potential of this product to use for wound care as a self-contained wound dressing or as a part of number of already existing novel wound dressing materials.

Sulfidation of Electrospun Vanadium Oxide Fiber Mats for Lithium-Ion Battery Electrodes

Energy storage plays a fundamental part in fulfilling the necessity of a more efficient, renewable, and environmentally friendly energy supply chain. Lithium-ion batteries are currently the most widely portable storage devices and typically employ transition metal oxides or dichalcogenides as electrode materials that promote redox reactions with lithium ions by either insertion or conversion mechanisms. For the latter, metal sulfides are prominent electrode materials owing to their high electrical conductivity and redox reversibility and high specific capacity. Vanadium sulfides exist in a range of crystal structures that can promote insertion of different ions in both anode and cathode side. Besides, they can also take part in conversion mechanisms in lithium-sulfur batteries. However, slow diffusion of lithium ions through the structure and high volumetric expansion compromises the average performance and stability of these materials. One strategy commonly adopted is the synthesis of hybrid nanostructured particles that combine a large surface area with short ion and electron transport pathways. The presence of conductive carbon in the hybrid material constrains the material expansion and ensures a conductive network during the conversion mechanism. Compared to other synthetic approaches, electrospinning enables the production of fibers constituted of nanosized structured materials. The continuous network of fibers forms free-standing mats that can be directly used as electrodes with no post-processing, coating or binder additives. Such mats allow continuous electron transport across the material while the synthesis itself promotes the homogeneous distribution of the components along the fibers, preventing particle agglomeration. In this work, vanadium oxide (VOx) mats are produced by electrospinning and converted to vanadium sulfide by thermal sulfidation process. The VOx fibers were prepared by the previously optimized electrospinning process.[1] The fiber mats were thermally treated under H2S/Ar atmosphere in different conditions to convert VOx into VSx. Lower synthesis temperatures promote a high degree of conversion while keeping smaller VSx domain size,and a higher interfacial contact between the carbon and the VSx phase. The VSx/C hybrid mats were directly applied as Li-ion battery electrodes and tested in different potential ranges to evaluate conversion and insertion mechanisms. The electrodes were paired with Li-ion discs in standard LP30 electrolyte using custom-built cell using spring-loaded titanium pistons.[2] The different VSx fibers were tested regarding redox profile, rate handling, and cycle stability. For the fibers with smaller VSx domain size, capacities up to 900 mAh/g were achieved when evaluating the whole active potential window, yet rate handling was compromised. When restricted to intercalation side capacities ranging of 150-280 mAh/g were observed, with good rate handling up to 2 A/g and full recovery of the initial capacity.

Free‐standing nitrogen‐doped graphene‐carbon nanofiber composite mats: electrospinning synthesis and application as anode material for lithium‐ion batteries

AbstractBACKGROUNDGraphene and carbon nanofibers have shown outstanding advantages as anode materials in lithium‐ion batteries (LIBs) because of their prominent electronic conductivity, outstanding flexibility, high theoretical specific capacity, high specific surface, and chemical durability. Free‐standing nanocomposite mats from graphene and carbon nanofibers, without any conductive additive and binder, could improve the weight energy density of the LIBs.RESULTSNitrogen‐doped carbon fiber‐reduced graphene oxide (NCNFs‐rGO) mats are fabricated by high‐temperature thermal treatment of graphene oxide/polyacrylonitrile (PAN‐GO) nanofiber composite mats via a simple electrospinning method. The resultant free‐standing NCNFs‐rGO mats which were systematically characterized by scanning electron microscopy, X‐ray diffraction, Raman spectroscopy, X‐ray photoelectron spectroscopy, and electrochemical properties as an anode for LIBs were also measured. Without any conductive additive and binder, the resultant free‐standing NCNFs‐rGO mats were directly used as an anode material in LIBs.CONCLUSIONThe LIBs with NCNFs‐rGO mats as anodes exhibited a high rate capability and long cycle stability owing to the structural integrity and highly electrical conductivity. © 2019 Society of Chemical Industry

Multiscale analysis of autotroph-heterotroph interactions in a high-temperature microbial community

Interactions among microbial community members can lead to emergent properties, such as enhanced productivity, stability, and robustness. Iron-oxide mats in acidic (pH 2–4), high-temperature (> 65 °C) springs of Yellowstone National Park contain relatively simple microbial communities and are well-characterized geochemically. Consequently, these communities are excellent model systems for studying the metabolic activity of individual populations and key microbial interactions. The primary goals of the current study were to integrate data collected in situ with in silico calculations across process-scales encompassing enzymatic activity, cellular metabolism, community interactions, and ecosystem biogeochemistry, as well as to predict and quantify the functional limits of autotroph-heterotroph interactions. Metagenomic and transcriptomic data were used to reconstruct carbon and energy metabolisms of an important autotroph (Metallosphaera yellowstonensis) and heterotroph (Geoarchaeum sp. OSPB) from the studied Fe(III)-oxide mat communities. Standard and hybrid elementary flux mode and flux balance analyses of metabolic models predicted cellular- and community-level metabolic acclimations to simulated environmental stresses, respectively. In situ geochemical analyses, including oxygen depth-profiles, Fe(III)-oxide deposition rates, stable carbon isotopes and mat biomass concentrations, were combined with cellular models to explore autotroph-heterotroph interactions important to community structure-function. Integration of metabolic modeling with in situ measurements, including the relative population abundance of autotrophs to heterotrophs, demonstrated that Fe(III)-oxide mat communities operate at their maximum total community growth rate (i.e. sum of autotroph and heterotroph growth rates), as opposed to net community growth rate (i.e. total community growth rate subtracting autotroph consumed by heterotroph), as predicted from the maximum power principle. Integration of multiscale data with ecological theory provides a basis for predicting autotroph-heterotroph interactions and community-level cellular organization.

Marsarchaeota are an aerobic archaeal lineage abundant in geothermal iron oxide microbial mats.

The discovery of archaeal lineages is critical to our understanding of the universal tree of life and evolutionary history of the Earth. Geochemically diverse thermal environments in Yellowstone National Park provide unprecedented opportunities for studying archaea in habitats that may represent analogues of early Earth. Here, we report the discovery and characterization of a phylum-level archaeal lineage proposed and herein referred to as the 'Marsarchaeota', after the red planet. The Marsarchaeota contains at least two major subgroups prevalent in acidic, microaerobic geothermal Fe(III) oxide microbial mats across a temperature range from ~50-80 °C. Metagenomics, single-cell sequencing, enrichment culturing and in situ transcriptional analyses reveal their biogeochemical role as facultative aerobic chemoorganotrophs that may also mediate the reduction of Fe(III). Phylogenomic analyses of replicate assemblies corresponding to two groups of Marsarchaeota indicate that they branch between the Crenarchaeota and all other major archaeal lineages. Transcriptomic analyses of several Fe(III) oxide mat communities reveal that these organisms were actively transcribing two different terminal oxidase complexes in situ and genes comprising an F420-dependent butanal catabolism. The broad distribution of Marsarchaeota in geothermal, microaerobic Fe(III) oxide mats suggests that similar habitat types probably played an important role in the evolution of archaea.

Neurogenic differentiation of adipose derived stem cells on graphene-based mat

Adipose derived stem cells (ADSCs) have been proved as an abundant and accessible cell source with the ability to differentiate into neuron-like cells. However, the low differentiation efficiency puts forward an important challenge to practical applications in clinic. Considering of the good biocompatibility of graphene-based materials and the potential interaction between graphene and cells mentioned in previous studies, herein, we investigated the effect of graphene oxide (GO) and reduced graphene oxide (rGO) mats on neurogenic differentiation of the ADSCs. We demonstrated the excellent capabilities of graphene-based mats, especially GO to support the neural differentiation of ADSCs. By comparing the observation under an optical microscope and fluorescence microscope, the conversion rate of neuron-like cells reached about 90%. We consider that GO mat is better for promoting the differentiation of ADSCs into neuron-like cells, which compared to rGO based platforms. Meanwhile, we made an analysis of the mechanism by which graphene induced the differentiation of ADSCs to neuron-like cells. The data obtained here highlight the effect of GO mat on neurogenic differentiation of ADSCs and implicate the potential of graphene-based materials in application of neural tissue engineering for the limited self-repair capability of nerve cells.

Hydrogen Peroxide Cycling in High-Temperature Acidic Geothermal Springs and Potential Implications for Oxidative Stress Response

Hydrogen peroxide (H2O2), superoxide (O2•-), and hydroxyl radicals (OH•) are produced in natural waters via ultraviolet (UV) light-induced reactions between dissolved oxygen (O2) and organic carbon, and further reaction of H2O2 and Fe(II) (i.e., Fenton chemistry). The temporal and spatial dynamics of H2O2 and other dissolved compounds (Fe(II), Fe(III), H2S, O2) were measured during a diel cycle (dark/light) in surface waters of three acidic geothermal springs (Beowulf Spring, One Hundred Springs Plain, and Echinus Geyser Spring; pH = 3-3.5, T = 68-80 °C) in Norris Geyser Basin, Yellowstone National Park. In situ analyses showed that H2O2 concentrations were lowest (ca. 1 μM) in geothermal source waters containing high dissolved sulfide (and where oxygen was below detection) and increased by two-fold (ca. 2-3 μM) in oxygenated waters corresponding to Fe(III)-oxide mat formation down the water channel. Small increases in dissolved oxygen and H2O2 were observed during peak photon flux, but not consistently across all springs sampled. Iron-oxide microbial mats were sampled for molecular analysis of ROS gene expression in two primary autotrophs of acidic Fe(III)-oxide mat ecosystems: Metallosphaera yellowstonensis (Archaea) and Hydrogenobaculum sp. (Bacteria). Expression (RT-qPCR) assays of specific stress-response genes (e.g., superoxide dismutase, peroxidases) of the primary autotrophs were used to evaluate possible changes in transcription across temporal, spatial and/or seasonal samples. Data presented here documented the presence of H2O2 and general correlation with dissolved oxygen. Moreover, two dominant microbial populations expressed ROS response genes throughout the day, but showed less expression of key genes during peak sunlight. Oxidative stress response genes (especially external peroxidases) were highly-expressed in microorganisms within Fe(III)-oxide mat communities, suggesting a significant role for these proteins during survival and growth in situ.

Preparation and characterization of electrospun PHBV/PEO mats: The role of solvent and PEO component

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/polyethylene oxide (PEO) mats were fabricated by electrospinning in different weight ratios (i.e., 100/0, 90/10, 80/20, 70/30, 60/40, 50/50, 0/100). In this paper, dichloromethane (DCM) has been used as potential solvent for electrospinning. In order to evaluate the influence of PEO and DCM on the final properties of PHBV mat, the following characterization techniques were employed: scanning electron microscopy, Fourier transform infrared attenuated total reflectance spectroscopy, X-ray diffraction analysis, thermogravimetric analysis, differential scanning calorimetry, and the test of mechanical properties, water contact angle, porosity analysis, swelling properties, water–vapor transmission rate (WVTR) and in vitro degradation behavior. All PHBV/PEO electrospun mats consist of randomly oriented and distinctly separated fibers. The average fiber diameters and the porosity were 738–1098 nm and 80–90 %, respectively. The water contact angle, swelling ratio, WVTR, and in vitro degradation behavior of PHBV/PEO electrospun mats were 124°–55°, 265–436 %, 1977–2610 g m−2 day−1, and 17–50 %, respectively. Besides, the crystallinity degree of PHBV/PEO electrospun mats has decreased with the increasing of PEO content. Therefore, PEO imparted PHBV/PEO electrospun mats on better properties, improving the nature defects of PHBV. In particular, PHBV/PEO 70/30 electrospun mat with optimizing performance, was considered the best candidate for potential scaffold in skin tissue engineering.

Assembly and Succession of Iron Oxide Microbial Mat Communities in Acidic Geothermal Springs.

Biomineralized ferric oxide microbial mats are ubiquitous features on Earth, are common in hot springs of Yellowstone National Park (YNP, WY, USA), and form due to direct interaction between microbial and physicochemical processes. The overall goal of this study was to determine the contribution of different community members to the assembly and succession of acidic high-temperature Fe(III)-oxide mat ecosystems. Spatial and temporal changes in Fe(III)-oxide accretion and the abundance of relevant community members were monitored over 70 days using sterile glass microscope slides incubated in the outflow channels of two acidic geothermal springs (pH = 3–3.5; temperature = 68–75°C) in YNP. Hydrogenobaculum spp. were the most abundant taxon identified during early successional stages (4–40 days), and have been shown to oxidize arsenite, sulfide, and hydrogen coupled to oxygen reduction. Iron-oxidizing populations of Metallosphaera yellowstonensis were detected within 4 days, and reached steady-state levels within 14–30 days, corresponding to visible Fe(III)-oxide accretion. Heterotrophic archaea colonized near 30 days, and emerged as the dominant functional guild after 70 days and in mature Fe(III)-oxide mats (1–2 cm thick). First-order rate constants of Fe(III)-oxide accretion ranged from 0.046 to 0.05 day−1, and in situ microelectrode measurements showed that the oxidation of Fe(II) is limited by the diffusion of O2 into the Fe(III)-oxide mat. The formation of microterracettes also implicated O2 as a major variable controlling microbial growth and subsequent mat morphology. The assembly and succession of Fe(III)-oxide mat communities follows a repeatable pattern of colonization by lithoautotrophic organisms, and the subsequent growth of diverse organoheterotrophs. The unique geochemical signatures and micromorphology of extant biomineralized Fe(III)-oxide mats are also useful for understanding other Fe(II)-oxidizing systems.

Carbon Dioxide Fixation by Metallosphaera yellowstonensis and Acidothermophilic Iron-Oxidizing Microbial Communities from Yellowstone National Park

The fixation of inorganic carbon has been documented in all three domains of life and results in the biosynthesis of diverse organic compounds that support heterotrophic organisms. The primary aim of this study was to assess carbon dioxide fixation in high-temperature Fe(III)-oxide mat communities and in pure cultures of a dominant Fe(II)-oxidizing organism (Metallosphaera yellowstonensis strain MK1) originally isolated from these environments. Protein-encoding genes of the complete 3-hydroxypropionate/4-hydroxybutyrate (3-HP/4-HB) carbon dioxide fixation pathway were identified in M. yellowstonensis strain MK1. Highly similar M. yellowstonensis genes for this pathway were identified in metagenomes of replicate Fe(III)-oxide mats, as were genes for the reductive tricarboxylic acid cycle from Hydrogenobaculum spp. (Aquificales). Stable-isotope ((13)CO2) labeling demonstrated CO2 fixation by M. yellowstonensis strain MK1 and in ex situ assays containing live Fe(III)-oxide microbial mats. The results showed that strain MK1 fixes CO2 with a fractionation factor of ∼2.5‰. Analysis of the (13)C composition of dissolved inorganic C (DIC), dissolved organic C (DOC), landscape C, and microbial mat C showed that mat C is from both DIC and non-DIC sources. An isotopic mixing model showed that biomass C contains a minimum of 42% C of DIC origin, depending on the fraction of landscape C that is present. The significance of DIC as a major carbon source for Fe(III)-oxide mat communities provides a foundation for examining microbial interactions that are dependent on the activity of autotrophic organisms (i.e., Hydrogenobaculum and Metallosphaera spp.) in simplified natural communities.

A facile one-step way to anchor noble metal (Au, Ag, Pd) nanoparticles on a reduced graphene oxide mat with catalytic activity for selective reduction of nitroaromatic compounds

A facile, one-step clean strategy has been utilized for anchoring noble metal (Au, Ag, Pd) nanoparticles onto the flat surface of two-dimensional (2D) graphene oxide (GO) nanosheets. Without using any additional reductants, surfactants or protecting ligands, the deposition of metallic noble metal (Au, Ag, Pd) nanoparticles on the partially reduced graphene oxide (PRGO) mat has been realized by a simple redox reaction between the noble metal precursors and GO in an aqueous solution. The main size distributions of the Au, Ag and Pd particles are centered on 1–20 nm, 3–10 nm and 0.5–3 nm, respectively. The as-obtained Au, Ag and Pd–PRGO nanocomposites display superb catalytic activities for the selective reduction of nitroaromatic compounds into the corresponding amino compounds under ambient conditions. The rates of reduction follow the sequence, Pd–PRGO > Ag–PRGO > Au–PRGO, suggesting that the smallest noble metal particles size affords the highest catalytic activity. In addition, considering that the Au, Ag and Pd–PRGO nanocomposites still hold the abundant functional groups of the original GO, these noble metal–PRGO composites maintain the excellent hydrophilic nature of GO, which provides a flexible platform for the further fabrication of PRGO–metal-based multicomponent functional materials by a wet-chemistry approach.

Metagenomic insights into the dominant Fe(II) oxidizing Zetaproteobacteria from an iron mat at Lō´ihi, Hawai´l

Zetaproteobacteria are among the most prevalent Fe(II)-oxidizing bacteria (FeOB) at deep-sea hydrothermal vents; however, knowledge about their environmental significance is limited. We provide metagenomic insights into an iron mat at the Lō´ihi Seamount, Hawai´l, revealing novel genomic information of locally dominant Zetaproteobacteria lineages. These lineages were previously estimated to account for ~13% of all local Zetaproteobacteria based on 16S clone library data. Biogeochemically relevant genes include nitrite reductases, which were previously not identified in Zetaproteobacteria, sulfide:quinone oxidases, and ribulose-1,5-bisphosphate carboxylase (RuBisCo). Genes assumed to be involved in Fe(II) oxidation correlate in synteny and share 87% amino acid similarity with those previously identified in the related Zetaproteobacterium Mariprofundus ferrooxydans PV-1. Overall, Zetaproteobacteria genes appear to originate primarily from within the Proteobacteria and the Fe(II)-oxidizing Leptospirillum spp. and are predicted to facilitate adaptation to a deep-sea hydrothermal vent environment in addition to microaerophilic Fe(II) and H2S oxidation. This dataset represents the first metagenomic study of FeOB from an iron oxide mat at a deep-sea hydrothermal habitat.

Microbial Iron Cycling in Acidic Geothermal Springs of Yellowstone National Park: Integrating Molecular Surveys, Geochemical Processes, and Isolation of Novel Fe-Active Microorganisms

Geochemical, molecular, and physiological analyses of microbial isolates were combined to study the geomicrobiology of acidic iron oxide mats in Yellowstone National Park. Nineteen sampling locations from 11 geothermal springs were studied ranging in temperature from 53 to 88°C and pH 2.4 to 3.6. All iron oxide mats exhibited high diversity of crenarchaeal sequences from the Sulfolobales, Thermoproteales, and Desulfurococcales. The predominant Sulfolobales sequences were highly similar to Metallosphaera yellowstonensis str. MK1, previously isolated from one of these sites. Other groups of archaea were consistently associated with different types of iron oxide mats, including undescribed members of the phyla Thaumarchaeota and Euryarchaeota. Bacterial sequences were dominated by relatives of Hydrogenobaculum spp. above 65–70°C, but increased in diversity below 60°C. Cultivation of relevant iron-oxidizing and iron-reducing microbial isolates included Sulfolobus str. MK3, Sulfobacillus str. MK2, Acidicaldus str. MK6, and a new candidate genus in the Sulfolobales referred to as Sulfolobales str. MK5. Strains MK3 and MK5 are capable of oxidizing ferrous iron autotrophically, while strain MK2 oxidizes iron mixotrophically. Similar rates of iron oxidation were measured for M. yellowstonensis str. MK1 and Sulfolobales str. MK5. Biomineralized phases of ferric iron varied among cultures and field sites, and included ferric oxyhydroxides, K-jarosite, goethite, hematite, and scorodite depending on geochemical conditions. Strains MK5 and MK6 are capable of reducing ferric iron under anaerobic conditions with complex carbon sources. The combination of geochemical and molecular data as well as physiological observations of isolates suggests that the community structure of acidic Fe mats is linked with Fe cycling across temperatures ranging from 53 to 88°C.

Neutrophilic Iron-Oxidizing “ Zetaproteobacteria ” and Mild Steel Corrosion in Nearshore Marine Environments

Microbiologically influenced corrosion (MIC) of mild steel in seawater is an expensive and enduring problem. Little attention has been paid to the role of neutrophilic, lithotrophic, iron-oxidizing bacteria (FeOB) in MIC. The goal of this study was to determine if marine FeOB related to Mariprofundus are involved in this process. To examine this, field incubations and laboratory microcosm experiments were conducted. Mild steel samples incubated in nearshore environments were colonized by marine FeOB, as evidenced by the presence of helical iron-encrusted stalks diagnostic of the FeOB Mariprofundus ferrooxydans, a member of the candidate class "Zetaproteobacteria." Furthermore, Mariprofundus-like cells were enriched from MIC biofilms. The presence of Zetaproteobacteria was confirmed using a Zetaproteobacteria-specific small-subunit (SSU) rRNA gene primer set to amplify sequences related to M. ferrooxydans from both enrichments and in situ samples of MIC biofilms. Temporal in situ incubation studies showed a qualitative increase in stalk distribution on mild steel, suggesting progressive colonization by stalk-forming FeOB. We also isolated a novel FeOB, designated Mariprofundus sp. strain GSB2, from an iron oxide mat in a salt marsh. Strain GSB2 enhanced uniform corrosion from mild steel in laboratory microcosm experiments conducted over 4 days. Iron concentrations (including precipitates) in the medium were used as a measure of corrosion. The corrosion in biotic samples (7.4 ± 0.1 mM) was significantly higher than that in abiotic controls (5.0 ± 0.1 mM). These results have important implications for the role of FeOB in corrosion of steel in nearshore and estuarine environments. In addition, this work shows that the global distribution of Zetaproteobacteria is far greater than previously thought.

Microbial Ecology of Fe (hydr)oxide Mats and Basaltic Rock from Vailulu'u Seamount, American Samoa

Microbial community analysis of a deep-sea volcanic and hydrothermal system at Vailulu'u Seamount yielded 89 new organisms and three detailed 16S-rRNA gene clone libraries (one rock and two microbial mats). Proteobacterial communities dominate in most environments, but important differences are found between microbial mats from distinctly different geochemical environments and for the rock surface. Many cultured organisms are metabolically and functionally diverse, displaying at least two of the tested functions: heterotrophy, Fe(II) and Mn(II) oxidation, and siderophore-production. Metabolic versatility of microorganisms is suggested as an important trait allowing diverse populations of bacteria to adapt to these environments.

3D Bi2WO6/TiO2 Hierarchical Heterostructure: Controllable Synthesis and Enhanced Visible Photocatalytic Degradation Performances

A three-dimensional (3D) multicomponent oxide, Bi2WO6/TiO2 as an example, hierarchical heterostructure was successfully synthesized as a mat via a simple and practical electrospinning-assisted route. The as-prepared hierarchical nanofibrous mat consisted of Bi2WO6 nanoplates growing aslant on the primary TiO2 nanofibers. Interestingly, the nanoplates were further composed of nanoparticles with a size of less than 20 nm. Bi2WO6 with different morphologies and microstructures could be obtained by adjusting the concentration of the precursor. From the mat (10 cm) to the nanoparticle (20 nm), this multicomponent oxide mat due to the self-supporting property could be layed or hung conveniently anywhere under solar irradiation and recycled easily. Due to the structure−property relationships, the 3D Bi2WO6/TiO2 hierarchical heterostructure exhibited enhanced visible photocatalytic activity over that of the bulk Bi2WO6/TiO2 powder (SSR), the Bi2WO6 nanoparticles (BWO), and the TiO2 sample in the decomposition of both acetaldehyde (CH3CHO) in air and rhodamine B (RhB) in water which are typical model pollutants. Close investigation revealed that the surface area, grain size, and hierarchical heterostructure of the as-prepared Bi2WO6/TiO2 mat could improve the photocatalytic activities.

Isolation and Distribution of a Novel Iron-Oxidizing Crenarchaeon from Acidic Geothermal Springs in Yellowstone National Park

Novel thermophilic crenarchaea have been observed in Fe(III) oxide microbial mats of Yellowstone National Park (YNP); however, no definitive work has identified specific microorganisms responsible for the oxidation of Fe(II). The objectives of the current study were to isolate and characterize an Fe(II)-oxidizing member of the Sulfolobales observed in previous 16S rRNA gene surveys and to determine the abundance and distribution of close relatives of this organism in acidic geothermal springs containing high concentrations of dissolved Fe(II). Here we report the isolation and characterization of the novel, Fe(II)-oxidizing, thermophilic, acidophilic organism Metallosphaera sp. strain MK1 obtained from a well-characterized acid-sulfate-chloride geothermal spring in Norris Geyser Basin, YNP. Full-length 16S rRNA gene sequence analysis revealed that strain MK1 exhibits only 94.9 to 96.1% sequence similarity to other known Metallosphaera spp. and less than 89.1% similarity to known Sulfolobus spp. Strain MK1 is a facultative chemolithoautotroph with an optimum pH range of 2.0 to 3.0 and an optimum temperature range of 65 to 75 degrees C. Strain MK1 grows optimally on pyrite or Fe(II) sorbed onto ferrihydrite, exhibiting doubling times between 10 and 11 h under aerobic conditions (65 degrees C). The distribution and relative abundance of MK1-like 16S rRNA gene sequences in 14 acidic geothermal springs containing Fe(III) oxide microbial mats were evaluated. Highly related MK1-like 16S rRNA gene sequences (>99% sequence similarity) were consistently observed in Fe(III) oxide mats at temperatures ranging from 55 to 80 degrees C. Quantitative PCR using Metallosphaera-specific primers confirmed that organisms highly similar to strain MK1 comprised up to 40% of the total archaeal community at selected sites. The broad distribution of highly related MK1-like 16S rRNA gene sequences in acidic Fe(III) oxide microbial mats is consistent with the observed characteristics and growth optima of Metallosphaera-like strain MK1 and emphasizes the importance of this newly described taxon in Fe(II) chemolithotrophy in acidic high-temperature environments of YNP.

Linking geochemical processes with microbial community analysis: successional dynamics in an arsenic‐rich, acid‐sulphate‐chloride geothermal spring

ABSTRACTThe source waters of acid‐sulphate‐chloride (ASC) geothermal springs located in Norris Geyser Basin, Yellowstone National Park contain several reduced chemical species, including H2, H2S, As(III), and Fe(II), which may serve as electron donors driving chemolithotrophic metabolism. Microorganisms thriving in these environments must also cope with high temperatures, low pH (∼3), and high concentrations of sulphide, As(III), and boron. The goal of the current study was to correlate the temporal and spatial distribution of bacterial and archaeal populations with changes in temperature and geochemical energy gradients occurring throughout a newly formed (redirected) outflow channel of an ASC spring. A suite of complimentary analyses including aqueous geochemistry, microscopy, solid phase identification, and 16S rDNA sequence distribution were used to correlate the appearance of specific microbial populations with biogeochemical processes mediating S, Fe, and As cycling and subsequent biomineralization of As(V)‐rich hydrous ferric oxide (HFO) mats. Rapid As(III) oxidation (maximum first order rate constants ranged from 4 to 5 min−1, t1/2 = 0.17 − 0.14 min) was correlated with the appearance of Hydrogenobaculum and Thiomonas–like populations, whereas the biogenesis of As(V)‐rich HFO microbial mats (mole ratios of As:Fe ∼0.7) was correlated with the appearance of Metallosphaera, Acidimicrobium, and Thiomonas–like populations. Several 16S sequences detected near the source were closely related to sequences of chemolithotrophic hyperthermophilic populations including Stygiolobus and Hydrogenobaculum organisms that are known H2 oxidizers. The use of H2, reduced S(–II,0), Fe(II) and perhaps As(III) by different organisms represented throughout the outflow channel was supported by thermodynamic calculations, confirming highly exergonic redox couples with these electron donors. Results from this work demonstrated that chemical energy gradients play an important role in establishing distinct community structure as a function of distance from geothermal spring discharge.