The Evolution Pathway of Ammonia-Oxidizing Archaea Shaped by Major Geological Events.

Primordial nitrification processes have been studied extensively using geochemical approaches, but the biological origination of nitrification remains unclear. Ammonia-oxidizing archaea (AOA) are widely distributed nitrifiers and implement the rate-limiting step in nitrification. They are hypothesized to have been important players in the global nitrogen cycle in Earth's early history. We performed systematic phylogenomic and marker gene analyses to elucidate the diversification timeline of AOA evolution. Our results suggested that the AOA ancestor experienced terrestrial geothermal environments at ∼1,165 Ma (1,928-880 Ma), and gradually evolved into mesophilic soil at ∼652 Ma (767-554 Ma) before diversifying into marine settings at ∼509 Ma (629-412 Ma) and later into shallow and deep oceans, respectively. Corroborated by geochemical evidence and modeling, the timing of key diversification nodes can be linked to the global magmatism and glaciation associated with the assembly and breakup of the supercontinent Rodinia, and the later oxygenation of the deep ocean. Results of this integrated study shed light on the geological forces that may have shaped the evolutionary pathways of the AOA, which played an important role in the ancient global nitrogen cycle.

Corrigendum: Active Anaerobic Archaeal Methanotrophs in Recently Emerged Cold Seeps of Northern South China Sea.

[This corrects the article DOI: 10.3389/fmicb.2020.612135.].

Impact of Terrestrial Input on Deep-Sea Benthic Archaeal Community Structure in South China Sea Sediments.

Archaea are widespread in marine sediments and play important roles in the cycling of sedimentary organic carbon. However, factors controlling the distribution of archaea in marine sediments are not well understood. Here we investigated benthic archaeal communities over glacial-interglacial cycles in the northern South China Sea and evaluated their responses to sediment organic matter sources and inter-species interactions. Archaea in sediments deposited during the interglacial period Marine Isotope Stage (MIS) 1 (Holocene) were significantly different from those in sediments deposited in MIS 2 and MIS 3 of the Last Glacial Period when terrestrial input to the South China Sea was enhanced based on analysis of the long-chain n-alkane C31. The absolute archaeal 16S rRNA gene abundance in subsurface sediments was highest in MIS 2, coincident with high sedimentation rates and high concentrations of total organic carbon. Soil Crenarchaeotic Group (SCG; Nitrososphaerales) species, the most abundant ammonia-oxidizing archaea in soils, increased dramatically during MIS 2, likely reflecting transport of terrestrial archaea during glacial periods with high sedimentation rates. Co-occurrence network analyses indicated significant association of SCG archaea with benthic deep-sea microbes such as Bathyarchaeota and Thermoprofundales in MIS 2 and MIS 3, suggesting potential interactions among these archaeal groups. Meanwhile, Thermoprofundales abundance was positively correlated with total organic carbon (TOC), along with n-alkane C31 and sedimentation rate, indicating that Thermoprofundales may be particularly important in processing of organic carbon in deep-sea sediments. Collectively, these results demonstrate that the composition of heterotrophic benthic archaea in the South China Sea may be influenced by terrestrial organic input in tune with glacial-interglacial cycles, suggesting a plausible link between global climate change and microbial population dynamics in deep-sea marine sediments.

Active Anaerobic Archaeal Methanotrophs in Recently Emerged Cold Seeps of Northern South China Sea.

Cold seep ecosystems are developed from methane-rich fluids in organic rich continental slopes, which are the source of various dense microbial and faunal populations. Extensive studies have been conducted on microbial populations in this unique environment; most of them were based on DNA, which could not resolve the activity of extant organisms. In this study, RNA and DNA analyses were performed to evaluate the active archaeal and bacterial communities and their network correlations, particularly those participating in the methane cycle at three sites of newly developed cold seeps in the northern South China Sea (nSCS). The results showed that both archaeal and bacterial communities were significantly different at the RNA and DNA levels, revealing a higher abundance of methane-metabolizing archaea and sulfate-reducing bacteria in RNA sequencing libraries. Site ROV07-01, which exhibited extensive accumulation of deceased Calyptogena clam shells, was highly developed, and showed diverse and active anaerobic archaeal methanotrophs (ANME)-2a/b and sulfate-reducing bacteria from RNA libraries. Site ROV07-02, located near carbonate crusts with few clam shell debris, appeared to be poorly developed, less anaerobic and less active. Site ROV05-02, colonized by living Calyptogena clams, could likely be intermediary between ROV07-01 and ROV07-02, showing abundant ANME-2dI and sulfate-reducing bacteria in RNA libraries. The high-proportions of ANME-2dI, with respect to ANME-2dII in the site ROV07-01 was the first report from nSCS, which could be associated with recently developed cold seeps. Both ANME-2dI and ANME-2a/b showed close networked relationships with sulfate-reducing bacteria; however, they were not associated with the same microbial operational taxonomic units (OTUs). Based on the geochemical gradients and the megafaunal settlements as well as the niche specificities and syntrophic relationships, ANMEs appeared to change in community structure with the evolution of cold seeps, which may be associated with the heterogeneity of their geochemical processes. This study enriched our understanding of more active sulfate-dependent anaerobic oxidation of methane (AOM) in poorly developed and active cold seep sediments by contrasting DNA- and RNA-derived community structure and activity indicators.

Population dynamics of methanogens and methanotrophs along the salinity gradient in Pearl River Estuary: implications for methane metabolism.

Methane, a major greenhouse gas, plays an important role in global carbon cycling and climate change. Methanogenesis is identified as an important process for methane formation in estuarine sediments. However, the metabolism of methane in the water columns of estuaries is not well understood. The goal of this research was to examine the dynamics in abundance and community composition of methanogens and methanotrophs, and to examine whether and how they take part in methane metabolism in the water columns from the lower Pearl River (freshwater) to the coastal South China Sea (seawater). Quantitative PCR (qPCR) and high-throughput sequencing results showed that the abundance of methanogens decreased with increasing salinity, suggesting that growth of these methanogens in the Pearl River Estuary may be influenced by high salinity. Also, the methane concentration in surface waters was lower than that in near-bottom waters at most sites, suggesting sediment methanogens are a likely source of methane. In the estuarine mixing zone, significantly high methane concentrations existed with the presence of salt-tolerant methanogens (e.g., Methanomicrobiaceae, Methanocella, Methanosaeta and Methanobacterium) and methanotrophs (e.g., Methylocystis and Methylococcaceae), which were found in brackish habitats. Furthermore, a number of methanotrophic OTUs (from pmoA gene sequence data) had specific positive correlations with methanogenic OTUs (from mcrA gene sequence data), and some of these methanogenic OTUs were correlated with concentrations of particulate organic carbon (POC). The results indicate that methanotrophs and methanogens may be intimately linked in methane metabolism attached with particles in estuarine waters.

Synthesis of zinc-gallate phosphors by biomineralization and their emission properties.

Reduction of target species by microorganisms and their subsequent precipitation into sparingly soluble mineral phase nanoparticles have been referred to as microbially mediated nanomaterial synthesis. Here, we describe the microbially mediated production of nano-dimensioned spinel structured zinc-gallate (ZnGa2O4) phosphors exhibiting different emission performance with varying substituted elements. Interestingly, in the microbially mediated phosphor production described herein, there were no reducible metal- and non-metal species composing the target minerals. By varying substituted elements, zinc-gallate phosphors present typical red, green, and blue (RGB) emission. An apparent whitish emission was accomplished by blending phosphors. A promising potential for white light produced by biosynthesized mixtures of Cr-, Mn-, and Co- substituted zinc-gallates representing RGB emissions was evidenced. Microbial activity supplied a reducing driving force and provided appropriate near neutral pH and reduced Eh conditions to thermodynamically precipitate spinel structured nanomaterials from supersaturated divalent and trivalent cations. This result complemented conventional biomineralization concepts and expanded the realm of biomanufacturing nanomaterials for further applications. STATEMENT OF SIGNIFICANCE: This study substantiated that circumstances of a suitable pH/Eh derived from bacterial activity, divalent/trivalent ion supply, buffering capacity, and supersaturation could precipitate spinel structure nanoparticles. Even though live or dead cells with membrane could enhance the nuclei generation, the spinel structured phases were produced regardless of existence of live or dead cells and reducible metal or non-metal species incorporating into the produced solid phases. This finding led to production of a series of metal-substituted zinc-gallates with specific RGB emission that can result in whitish light using simple blending. We believe our findings could expand the realm of nanomaterial synthesis using low cost, highly scalable bio-nanotechnology.

Improved ZnS nanoparticle properties through sequential NanoFermentation.

Sequential NanoFermentation (SNF) is a novel process which entails sparging microbially produced gas containing H2S from a primary reactor through a concentrated metal-acetate solution contained in a secondary reactor, thereby precipitating metallic sulfide nanoparticles (e.g., ZnS, CuS, or SnS). SNF holds an advantage over single reactor nanoparticle synthesis strategies, because it avoids exposing the microorganisms to high concentrations of toxic metal and sulfide ions. Also, by segregating the nanoparticle products from biological materials, SNF avoids coating nanoparticles with bioproducts that alter their desired properties. Herein, we report the properties of ZnS nanoparticles formed from SNF as compared with ones produced directly in a primary reactor (i.e., conventional NanoFermentation, or "CNF"), commercially available ZnS, and ZnS chemically synthesized by bubbling H2S gas through a Zn-acetate solution. The ZnS nanoparticles produced by SNF provided improved optical properties due to their smaller crystallite size, smaller overall particle sizes, reduced biotic surface coatings, and reduced structural defects. SNF still maintained the advantages of NanoFermentation technology over chemical synthesis including scalability, reproducibility, and lower hazardous waste burden.

Impacts of Methane on Carbon Dioxide Storage in Brine Formations.

In the context of geological carbon sequestration (GCS), carbon dioxide (CO2 ) is often injected into deep formations saturated with a brine that may contain dissolved light hydrocarbons, such as methane (CH4 ). In this multicomponent multiphase displacement process, CO2 competes with CH4 in terms of dissolution, and CH4 tends to exsolve from the aqueous into a gaseous phase. Because CH4 has a lower viscosity than injected CO2 , CH4 is swept up into a 'bank' of CH4 -rich gas ahead of the CO2 displacement front. On the one hand, this may provide a useful tracer signal of an approaching CO2 front. On the other hand, the emergence of gaseous CH4 is undesirable because it poses a leakage risk of a far more potent greenhouse gas than CO2 if the cap rock is compromised. Open fractures or faults and wells could result in CH4 contamination of overlying groundwater aquifers as well as surface emissions. We investigate this process through detailed numerical simulations for a large-scale GCS pilot project (near Cranfield, Mississippi) for which a rich set of field data is available. An accurate cubic-plus-association equation-of-state is used to describe the non-linear phase behavior of multiphase brine-CH4 -CO2 mixtures, and breakthrough curves in two observation wells are used to constrain transport processes. Both field data and simulations indeed show the development of an extensive plume of CH4 -rich (up to 90 mol%) gas as a consequence of CO2 injection, with important implications for the risk assessment of future GCS projects.

The response of archaeal species to seasonal variables in a subtropical aerated soil: insight into the low abundant methanogens.

Archaea are cosmopolitan in aerated soils around the world. While the dominance of Thaumarchaeota has been reported in most soils, the methanogens are recently found to be ubiquitous but with low abundances in the aerated soil globally. However, the seasonal changes of Archaea community in the aerated soils are still in the mist. In this study, we investigated the change of Archaea in the context of environmental variables over a period of 12 months in a subtropical soil on the Chongming Island, China. The results showed that Nitrososphaera spp. were the dominant archaeal population while the methanogens were in low proportions but highly diverse (including five genera: Methanobacterium, Methanocella, Methanosaeta, Methanosarcina, and Methanomassiliicoccus) in the aerated soil samples determined by high throughput sequencing. A total of 126 LSA correlations were found in the dataset including all the 72 archaeal OTUs and 8 environmental factors. A significance index defined as the pagerank score of each OTU divided by its relative abundance was used to evaluate the significance of each OTU. The results showed that five out of 17 methanogen OTUs were significantly positively correlated with temperature, suggesting those methanogens might increase with temperature rather than being dormant in the aerated soils. Given the metabolic response of methanogens to temperature under aerated soil conditions, their contribution to the global methane cycle warrants evaluation.

Temporal Dynamics of In-Field Bioreactor Populations Reflect the Groundwater System and Respond Predictably to Perturbation.

Temporal variability complicates testing the influences of environmental variability on microbial community structure and thus function. An in-field bioreactor system was developed to assess oxic versus anoxic manipulations on in situ groundwater communities. Each sample was sequenced (16S SSU rRNA genes, average 10,000 reads), and biogeochemical parameters are monitored by quantifying 53 metals, 12 organic acids, 14 anions, and 3 sugars. Changes in dissolved oxygen (DO), pH, and other variables were similar across bioreactors. Sequencing revealed a complex community that fluctuated in-step with the groundwater community and responded to DO. This also directly influenced the pH, and so the biotic impacts of DO and pH shifts are correlated. A null model demonstrated that bioreactor communities were driven in part not only by experimental conditions but also by stochastic variability and did not accurately capture alterations in diversity during perturbations. We identified two groups of abundant OTUs important to this system; one was abundant in high DO and pH and contained heterotrophs and oxidizers of iron, nitrite, and ammonium, whereas the other was abundant in low DO with the capability to reduce nitrate. In-field bioreactors are a powerful tool for capturing natural microbial community responses to alterations in geochemical factors beyond the bulk phase.

Manufacturing demonstration of microbially mediated zinc sulfide nanoparticles in pilot-plant scale reactors.

The thermophilic anaerobic metal-reducing bacterium Thermoanaerobacter sp. X513 efficiently produces zinc sulfide (ZnS) nanoparticles (NPs) in laboratory-scale (≤ 24-L) reactors. To determine whether this process can be up-scaled and adapted for pilot-plant production while maintaining NP yield and quality, a series of pilot-plant scale experiments were performed using 100-L and 900-L reactors. Pasteurization and N2-sparging replaced autoclaving and boiling for deoxygenating media in the transition from small-scale to pilot plant reactors. Consecutive 100-L batches using new or recycled media produced ZnS NPs with highly reproducible ~2-nm average crystallite size (ACS) and yields of ~0.5 g L(-1), similar to the small-scale batches. The 900-L pilot plant reactor produced ~320 g ZnS without process optimization or replacement of used medium; this quantity would be sufficient to form a ZnS thin film with ~120 nm thickness over 0.5 m width × 13 km length. At all scales, the bacteria produced significant amounts of acetic, lactic, and formic acids, which could be neutralized by the controlled addition of sodium hydroxide without the use of an organic pH buffer, eliminating 98 % of the buffer chemical costs. The final NP products were characterized using XRD, ICP-OES, TEM, FTIR, PL, DLS, HPLC, and C/N analyses, which confirmed that the growth medium without organic buffer enhanced the ZnS NP properties by reducing carbon and nitrogen surface coatings and supporting better dispersivity with similar ACS.

Community analysis of plant biomass-degrading microorganisms from Obsidian Pool, Yellowstone National Park.

The conversion of lignocellulosic biomass into biofuels can potentially be improved by employing robust microorganisms and enzymes that efficiently deconstruct plant polysaccharides at elevated temperatures. Many of the geothermal features of Yellowstone National Park (YNP) are surrounded by vegetation providing a source of allochthonic material to support heterotrophic microbial communities adapted to utilize plant biomass as a primary carbon and energy source. In this study, a well-known hot spring environment, Obsidian Pool (OBP), was examined for potential biomass-active microorganisms using cultivation-independent and enrichment techniques. Analysis of 33,684 archaeal and 43,784 bacterial quality-filtered 16S rRNA gene pyrosequences revealed that archaeal diversity in the main pool was higher than bacterial; however, in the vegetated area, overall bacterial diversity was significantly higher. Of notable interest was a flooded depression adjacent to OBP supporting a stand of Juncus tweedyi, a heat-tolerant rush commonly found growing near geothermal features in YNP. The microbial community from heated sediments surrounding the plants was enriched in members of the Firmicutes including potentially (hemi)cellulolytic bacteria from the genera Clostridium, Anaerobacter, Caloramator, Caldicellulosiruptor, and Thermoanaerobacter. Enrichment cultures containing model and real biomass substrates were established at a wide range of temperatures (55-85 °C). Microbial activity was observed up to 80 °C on all substrates including Avicel, xylan, switchgrass, and Populus sp. Independent of substrate, Caloramator was enriched at lower (<65 °C) temperatures while highly active cellulolytic bacteria Caldicellulosiruptor were dominant at high (>65 °C) temperatures.

Stoichiometry and temperature sensitivity of methanogenesis and CO2 production from saturated polygonal tundra in Barrow, Alaska.

Arctic permafrost ecosystems store ~50% of global belowground carbon (C) that is vulnerable to increased microbial degradation with warmer active layer temperatures and thawing of the near surface permafrost. We used anoxic laboratory incubations to estimate anaerobic CO2 production and methanogenesis in active layer (organic and mineral soil horizons) and permafrost samples from center, ridge and trough positions of water-saturated low-centered polygon in Barrow Environmental Observatory, Barrow AK, USA. Methane (CH4 ) and CO2 production rates and concentrations were determined at -2, +4, or +8 °C for 60 day incubation period. Temporal dynamics of CO2 production and methanogenesis at -2 °C showed evidence of fundamentally different mechanisms of substrate limitation and inhibited microbial growth at soil water freezing points compared to warmer temperatures. Nonlinear regression better modeled the initial rates and estimates of Q10 values for CO2 that showed higher sensitivity in the organic-rich soils of polygon center and trough than the relatively drier ridge soils. Methanogenesis generally exhibited a lag phase in the mineral soils that was significantly longer at -2 °C in all horizons. Such discontinuity in CH4 production between -2 °C and the elevated temperatures (+4 and +8 °C) indicated the insufficient representation of methanogenesis on the basis of Q10 values estimated from both linear and nonlinear models. Production rates for both CH4 and CO2 were substantially higher in organic horizons (20% to 40% wt. C) at all temperatures relative to mineral horizons (<20% wt. C). Permafrost horizon (~12% wt. C) produced ~5-fold less CO2 than the active layer and negligible CH4 . High concentrations of initial exchangeable Fe(II) and increasing accumulation rates signified the role of iron as terminal electron acceptors for anaerobic C degradation in the mineral horizons.

Metagenomes from thawing low-soil-organic-carbon mineral cryosols and permafrost of the canadian high arctic.

Microbial release of greenhouse gases from thawing permafrost is a global concern. Seventy-six metagenomes were generated from low-soil-organic-carbon mineral cryosols from Axel Heiberg Island, Nunavut, Canada, during a controlled thawing experiment. Permafrost thawing resulted in an increase in anaerobic fermenters and sulfate-reducing bacteria but not methanogens.

Trends and future challenges in sampling the deep terrestrial biosphere.

Research in the deep terrestrial biosphere is driven by interest in novel biodiversity and metabolisms, biogeochemical cycling, and the impact of human activities on this ecosystem. As this interest continues to grow, it is important to ensure that when subsurface investigations are proposed, materials recovered from the subsurface are sampled and preserved in an appropriate manner to limit contamination and ensure preservation of accurate microbial, geochemical, and mineralogical signatures. On February 20th, 2014, a workshop on "Trends and Future Challenges in Sampling The Deep Subsurface" was coordinated in Columbus, Ohio by The Ohio State University and West Virginia University faculty, and sponsored by The Ohio State University and the Sloan Foundation's Deep Carbon Observatory. The workshop aims were to identify and develop best practices for the collection, preservation, and analysis of terrestrial deep rock samples. This document summarizes the information shared during this workshop.

Scalable production of microbially mediated zinc sulfide nanoparticles and application to functional thin films.

A series of semiconducting zinc sulfide (ZnS) nanoparticles were scalably, reproducibly, controllably and economically synthesized with anaerobic metal-reducing Thermoanaerobacter species. These bacteria reduced partially oxidized sulfur sources to sulfides that extracellularly and thermodynamically incorporated with zinc ions to produce sparingly soluble ZnS nanoparticles with ∼5nm crystallites at yields of ∼5gl(-1)month(-1). A predominant sphalerite formation was facilitated by rapid precipitation kinetics, a low cation/anion ratio and a higher zinc concentration compared to background to produce a naturally occurring hexagonal form at the low temperature, and/or water adsorption in aqueous conditions. The sphalerite ZnS nanoparticles exhibited narrow size distribution, high emission intensity and few native defects. Scale-up and emission tunability using copper doping were confirmed spectroscopically. Surface characterization was determined using Fourier transform infrared and X-ray photoelectron spectroscopies, which confirmed amino acid as proteins and bacterial fermentation end products not only maintaining a nano-dimensional average crystallite size, but also increasing aggregation. The application of ZnS nanoparticle ink to a functional thin film was successfully tested for potential future applications.

Commercial DNA extraction kits impact observed microbial community composition in permafrost samples.

The total community genomic DNA (gDNA) from permafrost was extracted using four commercial DNA extraction kits. The gDNAs were compared using quantitative real-time PCR (qPCR) targeting 16S rRNA genes and bacterial diversity analyses obtained via 454 pyrosequencing of the 16S rRNA (V3 region) amplified in single or nested PCR. The FastDNA(®) SPIN (FDS) Kit provided the highest gDNA yields and 16S rRNA gene concentrations, followed by MoBio PowerSoil(®) (PS) and MoBio PowerLyzer™ (PL) kits. The lowest gDNA yields and 16S rRNA gene concentrations were from the Meta-G-Nome™ (MGN) DNA Isolation Kit. Bacterial phyla identified in all DNA extracts were similar to that found in other soils and were dominated by Actinobacteria, Firmicutes, Gemmatimonadetes, Proteobacteria, and Acidobacteria. Weighted UniFrac and statistical analyses indicated that bacterial community compositions derived from FDS, PS, and PL extracts were similar to each other. However, the bacterial community structure from the MGN extracts differed from other kits exhibiting higher proportions of easily lysed ß- and γ-Proteobacteria and lower proportions of Actinobacteria and Methylocystaceae important in carbon cycling. These results indicate that gDNA yields differ between the extraction kits, but reproducible bacterial community structure analysis may be accomplished using gDNAs from the three bead-beating lysis extraction kits.

Hexavalent chromium reduction under fermentative conditions with lactate stimulated native microbial communities.

Microbial reduction of toxic hexavalent chromium (Cr(VI)) in-situ is a plausible bioremediation strategy in electron-acceptor limited environments. However, higher [Cr(VI)] may impose stress on syntrophic communities and impact community structure and function. The study objectives were to understand the impacts of Cr(VI) concentrations on community structure and on the Cr(VI)-reduction potential of groundwater communities at Hanford, WA. Steady state continuous flow bioreactors were used to grow native communities enriched with lactate (30 mM) and continuously amended with Cr(VI) at 0.0 (No-Cr), 0.1 (Low-Cr) and 3.0 (High-Cr) mg/L. Microbial growth, metabolites, Cr(VI), 16S rRNA gene sequences and GeoChip based functional gene composition were monitored for 15 weeks. Temporal trends and differences in growth, metabolite profiles, and community composition were observed, largely between Low-Cr and High-Cr bioreactors. In both High-Cr and Low-Cr bioreactors, Cr(VI) levels were below detection from week 1 until week 15. With lactate enrichment, native bacterial diversity substantially decreased as Pelosinus spp., and Sporotalea spp., became the dominant groups, but did not significantly differ between Cr concentrations. The Archaea diversity also substantially decreased after lactate enrichment from Methanosaeta (35%), Methanosarcina (17%) and others, to mostly Methanosarcina spp. (95%). Methane production was lower in High-Cr reactors suggesting some inhibition of methanogens. Several key functional genes were distinct in Low-Cr bioreactors compared to High-Cr. Among the Cr resistant microbes, Burkholderia vietnamiensis, Comamonas testosterone and Ralstonia pickettii proliferated in Cr amended bioreactors. In-situ fermentative conditions facilitated Cr(VI) reduction, and as a result 3.0 mg/L Cr(VI) did not impact the overall bacterial community structure.

Scalable economic extracellular synthesis of CdS nanostructured particles by a non-pathogenic thermophile.

We report microbially facilitated synthesis of cadmium sulfide (CdS) nanostructured particles (NP) using anaerobic, metal-reducing Thermoanaerobacter sp. The extracellular CdS crystallites were <10 nm in size with yields of ~3 g/L of growth medium/month with demonstrated reproducibility and scalability up to 24 L. During synthesis, Thermoanaerobacter cultures reduced thiosulfate and sulfite salts to H2S, which reacted with Cd²âº cations to produce thermodynamically favored NP in a single step at 65 °C with catalytic nucleation on the cell surfaces. Photoluminescence (PL) analysis of dry CdS NP revealed an exciton-dominated PL peak at 440 nm, having a narrow full width at half maximum of 10 nm. A PL spectrum of CdS NP produced by dissimilatory sulfur reducing bacteria was dominated by features associated with radiative exciton relaxation at the surface. High reproducibility of CdS NP PL features important for scale-up conditions was confirmed from test tubes to 24 L batches at a small fraction of the manufacturing cost associated with conventional inorganic NP production processes.

Kinetics of methane hydrate decomposition studied via in situ low temperature X-ray powder diffraction.

Gas hydrate is known to have a slowed decomposition rate at ambient pressure and temperatures below the melting point of ice. As hydrate exothermically decomposes, gas is released and water of the clathrate cages transforms into ice. Based on results from the decomposition of three nominally similar methane hydrate samples, the kinetics of two regions, 180-200 and 230-260 K, within the overall decomposition range 140-260 K, were studied by in situ low temperature X-ray powder diffraction. The kinetic rate constants, k(a), and the reaction mechanisms, n, for ice formation from methane hydrate were determined by the Avrami model within each region, and activation energies, E(a), were determined by the Arrhenius plot. E(a) determined from the data for 180-200 K was 42 kJ/mol and for 230-260 K was 22 kJ/mol. The higher E(a) in the colder temperature range was attributed to a difference in the microstructure of ice between the two regions.