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Microbial assembly and metabolic potential in the subsurface critical zone (SCZ) are substantially impacted by subsurface geochemistry and hydrogeology, selecting for microbes distinct from those in surficial soils. In this study, we integrated metagenomics and geochemistry to elucidate how microbial composition and metabolic potential are shaped and impacted by vertical variations in geochemistry and hydrogeology in terrestrial subsurface sediment. A sediment core from an uncontaminated, pristine well at Oak Ridge Field Research Center in Oak Ridge, Tennessee, including the shallow subsurface, vadose zone, capillary fringe, and saturated zone, was used in this study. Our results showed that subsurface microbes were highly localized and that communities were rarely interconnected. Microbial community composition as well as metabolic potential in carbon and nitrogen cycling varied even over short vertical distances. Further analyses indicated a strong depth-related covariation of community composition with a subset of 12 environmental variables. An analysis of dissolved organic carbon (DOC) quality via ultrahigh resolution mass spectrometry suggested that the SCZ was generally a low-carbon environment, with the relative portion of labile DOC decreasing and that of recalcitrant DOC increasing along the depth, selecting microbes from copiotrophs to oligotrophs and also impacting the microbial metabolic potential in the carbon cycle. Our study demonstrates that sediment geochemistry and hydrogeology are vital in the selection of distinct microbial populations and metabolism in the SCZ. IMPORTANCE In this study, we explored the links between geochemical parameters, microbial community structure and metabolic potential across the depth of sediment, including the shallow subsurface, vadose zone, capillary fringe, and saturated zone. Our results revealed that microbes in the terrestrial subsurface can be highly localized, with communities rarely being interconnected along the depth. Overall, our research demonstrates that sediment geochemistry and hydrogeology are vital in the selection of distinct microbial populations and metabolic potential in different depths of subsurface terrestrial sediment. Such studies correlating microbial community analyses and geochemistry analyses, including high resolution mass spectrometry analyses of natural organic carbon, will further the fundamental understanding of microbial ecology and biogeochemistry in subsurface terrestrial ecosystems and will benefit the future development of predictive models on nutrient turnover in these environments.

Knowledge of dynamic interactions between natural organic matter (NOM) and microbial communities is critical not only to delineate the routes of NOM degradation/transformation and carbon (C) fluxes, but also to understand microbial community evolution and succession in ecosystems. Yet, these processes in subsurface environments are usually studied independently, and a comprehensive view has been elusive thus far. In this study, we fed sediment-derived dissolved organic matter (DOM) to groundwater microbes and continually analyzed microbial transformation of DOM over a 50-day incubation. To document fine-scale changes in DOM chemistry, we applied high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and soft X-ray absorption spectroscopy (sXAS). We also monitored the trajectory of microbial biomass, community structure and activity over this time period. Together, these analyses provided an unprecedented comprehensive view of interactions between sediment-derived DOM and indigenous subsurface groundwater microbes. Microbial decomposition of labile C in DOM was immediately evident from biomass increase and total organic carbon (TOC) decrease. The change of microbial composition was closely related to DOM turnover: microbial community in early stages of incubation was influenced by relatively labile tannin- and protein-like compounds; while in later stages the community composition evolved to be most correlated with less labile lipid- and lignin-like compounds. These changes in microbial community structure and function, coupled with the contribution of microbial products to DOM pool affected the further transformation of DOM, culminating in stark changes to DOM composition over time. Our study demonstrates a distinct response of microbial communities to biotransformation of DOM, which improves our understanding of coupled interactions between sediment-derived DOM, microbial processes, and community structure in subsurface groundwater.

Pu L3 x-ray absorption fine structure spectra demonstrate that although the Pu sublattice remains the ordered part of the Pu distribution, the nearest-neighbor O atoms even at x=o are found in a multisite distribution with Pu-O distances consistent with the stable incorporation of OH- into the PuO2 lattice.

Research has been conducted on the formamidopyrimidine-DNA glycosylase, a protein important for the excision repair of the oxidatively damaged DNA in Escherichia coli. Results indicate that zinc-associated motif is essential for the damaged DNA recognition.

Most of the uranium in uranium-contaminated soils exist as discrete particulates of hexavalent uranium, including phosphates, hydroxides and ill-defined organic complexes. This can be gleaned from data derived from a combination of X-ray absorption, optical luminescence and Raman vibrational spectroscopies applied on contaminated soils from the Dept. of Energy's former uranium facility in Fernald, OH. Complementary spectroscopic techniques allowed the identification of specific chemical forms of uranium in the soil, namely, autenite-like and schoepite-like phases.

A comparison of shifts in peak frequencies of samarium substituted yttrium aluminum garnet (Sm:YAG) and ruby fluorescence spectra as well as in the nitrogen vibron Raman spectrum is given. Calibration is done from 6 to 820 Kelvin and 0 to 25 gigapascal temperature and pressure ranges, respectively. Frequency shift comparison for ruby is done at temperatures less than 673 Kelvin. The nitrogen vibron and ruby pressure scales are presented and used in the pressure measurements at high temperatures. Shifts in Sm:YAG fluorescence in these ranges are negligible. Some Sm:YAG frequency shift applications and spectral data gathering suggestions are also discussed.

Incoherent inelastic neutron scattering is used to probe the effects of dihydrogen bonding on the vibrational dynamics in the molecular crystal of ammonia borane. The thermal neutron energy loss spectra of 11B enriched ammonia borane isotopomers (11BH3NH3, 11BD3NH3, and 11BH3ND3) are presented and compared to the vibrational power spectrum calculated using ab initio molecular dynamics. A harmonic vibrational analysis on NH3BH3 clusters was also explored to check for consistency with experiment and the power spectrum. The measured neutron spectra and computed ab initio power spectrum compare extremely well (50–500 cm-1). Some assignment of modes to simple harmonic motion, e.g., NH3 and BH3 torsion in the molecular crystal is possible, and it is confirmed that the lowest modes are dominated by collective motion. We show that the vibrational dynamics as modeled with ab initio molecular dynamics provides a more complete description of anharmonic and collective dynamics in the low frequency region of the inelastic incoherent neutron scattering spectra when compared to the conventional harmonic approach. [ABSTRACT FROM AUTHOR]

Raman spectra of single crystal ammonia borane, NH3BH3, were recorded as a function of temperature from 88 to 300 K using Raman microscopy and a variable temperature stage. The orthorhombic to orientationally disordered tetragonal phase transition at 225 K was clearly evident from the decrease in the number of vibrational modes. However, some of the modes in the orthorhombic phase appeared to merge 10–12 K below the phase transition perhaps suggesting the presence of an intermediate phase. Factor group analysis of vibrational spectra for both orthorhombic and tetragonal phase is provided. In addition, electronic structure calculations are used to assist in the interpretation and assignment of the normal modes. [ABSTRACT FROM AUTHOR]