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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Comparing the response of the indigenous microbial community to crude oil amendment in oxic versus hypoxic conditions

The Caspian Sea is the world’s largest landlocked saline lake which lies between Europe and Asia. This region is particularly known for its large-scale oil reserves, pipelines, and drilling activities, which have contributed to the environmental decline of this lake. In addition to pollution from the petroleum industry, drainage from various river basins brings an influx of residential, industrial, and agricultural effluents that induce eutrophication and hypoxic conditions in deeper, colder waters, creating an oxygen gradient. The temperature and oxygen stratification in this environment has presented a unique opportunity to investigate the potential of the biodegradative processes carried out by the indigenous microbial community. We believe these indigenous microbes possess different metabolic capabilities to degrade oil as they adapted to declining oxygen concentrations and temperatures with increasing depths over a prolonged period. Hence, community structure and composition will vary with depth. Microcosms were set up to observe the indigenous microbial reaction after a 60 ppm native crude oil amendment over 115 days. Surface water microcosms were incubated at 28ºC and aerated while deep water microcosms were incubated at 8ºC under anaerobic conditions. These two environmental conditions represent the temperature and oxygen extremes along the gradient and were selected as we try to simulate the indigenous community’s response to this oil contamination. DNA was extracted and amplified from these microcosms and sequenced. Bioinformatic analysis was performed to track changes in the abundance of taxa present and biodiversity over different time points to show the progression of community structure. All microcosms showed the presence of hydrocarbon-degrading phyla, whose presence is consistent with other reports from oil-enriched environments. However, distinct communities were observed in oxic versus hypoxic microcosms. Orders of Bacteria related to sulfate and nitrogen cycling were found in hypoxic microcosms, indicating a possible mechanism for the anaerobic biodegradation of crude oil. GC-MS analysis of initial and final microcosms also provided evidence of degradation of hydrocarbon fractions in both warm, oxic and cold, hypoxic conditions.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2001

Effects of Potassium Permanganate Oxidation on Subsurface Microbial Activity

In situ chemical oxidation has the potential for degrading large quantities of organic contaminants and can be more effective and timely than traditional ex situ treatment methods. However, there is a need to better characterize the potential effects of this treatment on natural processes. This study focuses on potential inhibition to anaerobic dechlorination of trichloroethene (TCE) in soils from a large manufacturing facility as a result of in situ oxidation using potassium permanganate (KMn04)Previous microcosm studies established that natural attenuation occurs on-site and that it is enhanced by the addition of ethanol to the system. A potential remediation scheme for the site involves the use of potassium permanganate to reduce levels of TCE in heavily contaminated areas, then to inject ethanol into the system to "neutralize" excess oxidant and enhance microbial degradation. However, it is currently unknown whether the exposure of indigenous microbial populations to potassium permanganate may adversely affect biological reductive dechlorination by these microorganisms. Consequently, additional microcosm studies were conducted to evaluate this remediation scheme and assess the effect of potassium permanganate addition on biological reductive dechlorination of TCE. Samples of subsurface soil and groundwater were collected from a TCE-impacted area of the site. A portion of the soil was pretreated with nutrients and ethanol to stimulate microbial activity, while the remainder of the soil was left unamended. Soil/groundwater microcosms were prepared in sealed vials using the nutrient-amended and unamended soils, and the effects of potassium permanganate addition were evaluated using two permanganate concentrations (0.8 and 2.4 percent) and two contact times (1 and 3 weeks). TCE was then re-added to each microcosm and TCE and dichloroethene (DCE) concentrations were monitored to determine the degree to which microbial dechlorination occurred following chemical oxidation. Evidence of microbial degradation was generally detected within four weeks after TCE addition. Increases in DCE concentrations were consistent with decreases in TCE. The concentration of TCE in the nutrient-amended samples exposed to 2.4% KMnO4 for one week degraded somewhat more slowly than the samples exposed to the 0.8% KMnO4. The rates of degradation did not correlate with the length of KMn04 exposure for the nutrient-amended microcosms. Microbial degradation of TCE in the unamended microcosms was generally similar to that observed in the nutrient-amended microcosms. One treatment condition (unamended, one week exposure, 2.4% KMnO4) was exposed to elevated levels of ethanol and showed little evidence of degradation. It is suspected that the high levels of ethanol were toxic to the microorganisms. The results of the study indicate that exposure of indigenous soil and groundwater microbial populations to KMnO4 at concentrations of 0.8 to 2.4% do not impair the ability of the microbial populations to dechlorinate TCE. Consequently, the combination of chemical oxidation followed by enhanced biological reductive dechlorination appears to be a viable remedial strategy for highly-impacted subsurface areas of the site.

Rowland, Martin A.↗
DOE OSTI2018

Impacts of Glutaraldehyde on Microbial Community Structure and Degradation Potential in Streams Impacted by Hydraulic Fracturing

The environmental impacts of hydraulic fracturing, particularly those of surface spills in aquatic ecosystems, are not fully understood. The goals of this study were to (1) understand the effect of previous exposure to hydraulic fracturing fluids on aquatic microbial community structure and (2) examine the impacts exposure has on biodegradation potential of the biocide glutaraldehyde. Microcosms were constructed from hydraulic fracturing-impacted and nonhydraulic fracturing-impacted streamwater within the Marcellus shale region in Pennsylvania. Microcosms were amended with glutaraldehyde and incubated aerobically for 56 days. Microbial community adaptation to glutaraldehyde was monitored using 16S rRNA gene amplicon sequencing and quantification by qPCR. Abiotic and biotic glutaraldehyde degradation was measured using ultra-performance liquid chromatography--high resolution mass spectrometry and total organic carbon. It was found that nonhydraulic fracturing-impacted microcosms biodegraded glutaraldehyde faster than the hydraulic fracturing-impacted microcosms, showing a decrease in degradation potential after exposure to hydraulic fracturing activity. Hydraulic fracturing-impacted microcosms showed higher richness after glutaraldehyde exposure compared to unimpacted streams, indicating an increased tolerance to glutaraldehyde in hydraulic fracturing impacted streams. Beta diversity and differential abundance analysis of sequence count data showed different bacterial enrichment for hydraulic fracturing-impacted and nonhydraulic fracturing-impacted microcosms after glutaraldehyde addition. These findings demonstrated a lasting effect on microbial community structure and glutaraldehyde degradation potential in streams impacted by hydraulic fracturing operations.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1998

Mineralization of Bacteria in Terrestrial Basaltic Rocks: Comparison With Possible Biogenic Features in Martian Meteorite Allan Hills 84001

The identification of biogenic features altered by diagenesis or mineralization is important in determining whether specific features in terrestrial rocks and in meteorites may have a biogenic origin. Unfortunately, few studies have addressed the formation of biogenic features in igneous rocks, which may be important to these phenomena, including the controversy over possible biogenic features in basaltic martian meteorite ALH84001. To explore the presence of biogenic features in igneous rocks, we examined microcosms growing in basaltic small-scale experimental growth chambers or microcosms. Microbial communities were harvested from aquifers of the Columbia River Basalt (CRB) group and grown in a microcosm containing unweathered basalt chips and groundwater (technique described in. These microcosms simulated natural growth conditions in the deep subsurface of the CRB, which should be a good terrestrial analog for any putative martian subsurface ecosystem that may have once included ALH84001. Here we present new size measurements and photomicrographs comparing the putative martian fossils to biogenic material in the CRB microcosms. The range of size and shapes of the biogenic features on the CRB microcosm chips overlaps with and is similar to those on ALH84001 chips. Although this present work does not provide evidence for the biogenicity of ALH84001 features, we believe that, based on criteria of size, shape, and general morphology, a biogenic interpretation for the ALH84001 features remains plausible.

Thomas-Keprta, K. L.↗
DOE OSTI2021

Impact of organic acids and sulfate on the biogeochemical properties of soil from urban subsurface environments

Urban subsurface environments are often different from undisturbed subsurface environments due to the impacts of human activities. For example, deterioration of underground infrastructure can introduce elevated levels of Ca, Fe, and heavy metals into subsurface soils and groundwater. Likewise, leakage from sewer systems can lead to contamination by organic C, N, S, and P. However, the impact of these organic and inorganic compounds on biogeochemical processes including microbial redox reactions, mineral transformations, and microbial community transitions in urban subsurface environments is poorly understood. Here we conducted a microcosm experiment with soil samples from an urban construction site to investigate the possible biotic and abiotic processes impacted when sulfate and acetate or lactate were introduced into an urban subsurface environment. In the top-layer soil (0-0.3 m) microcosms, which were highly alkaline (pH > 10), the major impact was on abiotic processes such as secondary mineral precipitation. In the mid-layer (2-3 m) soil microcosms, the rate of Fe(III)-reduction and the amount of Fe(II) produced were greatly impacted by the specific organic acid added, and sulfate-reduction was not observed until after Fe(III)-reduction was complete. Near the end of the incubation, some genera related to syntrophic acetate oxidation and methanogenesis were observed in the lactateamended microcosms. In the bottom-layer (7-8 m) soil microcosms, the rate of Fe(III)-reduction and the amount of Fe(II) produced were affected by the concentration of amended sulfate. Sulfate-reduction was concurrent with Fe(III)-reduction, suggesting that Fe(II) production was likely due to abiotic reduction of Fe(III) by sulfide produced by microbial sulfate reduction. The slightly acidic initial pH (~5.8) of the mid-soil system was a major factor controlling sequential microbial Fe(III) and sulfate reduction versus parallel Fe(III) and sulfate reduction in the bottom soil system, which had a neutral initial pH (~7.2). Finally, 16S rRNA gene-based community analysis revealed a variety of indigenous microbial groups including alkaliphiles, dissimilatory iron and sulfate reducers, syntrophes, and methanogens tightly coupled with, and impacted by, these complex abiotic and biogeochemical processes occurring in urban subsurface environments.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Interactions among decaying leaf litter, root litter and soil organic matter vary with mycorrhizal type

Abstract Root‐derived inputs are increasingly viewed as primary controls of soil organic matter (SOM) formation; however, we have a limited understanding of how root decay rates depend on soil factors, and how decaying roots influence the breakdown of leaf litter and SOM. We incubated root and leaf litter (alone and in combination) from arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) trees in soils collected from forest plots dominated by AM and ECM trees in a factorial design. In each microcosm, we quantified litter decay rates and the effects of decaying litters on soil C balance. We hypothesized that (1) AM root litters would decompose faster than ECM root litters, (2) root litter decay would be greatest when decomposed in “home” soils (e.g. AM litters in AM soils and ECM litters in ECM soils) and (3) root and leaf litters would decompose faster when decaying in the same microcosms than when decaying in separate microcosms, resulting in the largest CO 2 losses. Overall, AM root litter decomposed faster than ECM root litter, and the magnitude of this effect depended on soil origin. AM litters decayed fastest in AM soils, but ECM and mixed AM–ECM litters were unaffected by soil origin. Decaying roots increased leaf litter mass loss, but only in microcosms containing soils of the same origin (e.g. AM litters in AM soils; mixed litters in mixed soils). Carbon losses were dominated by microbial respiration, and the magnitude of this flux depended on litter type and soil origin. When leaves and roots decayed together, respiratory losses exceeded those from microcosms containing leaves and roots alone, with the largest losses occurring in each litters' “home” soil. In AM soils, elevated losses were driven by roots accelerating leaf decay, while in ECM soils, elevated losses resulted from roots and leaves accelerating the decay of SOM; in mixed soils, root‐induced increases in leaf and SOM decay contributed to elevated C losses. Synthesis . Our results suggest that root, leaf and SOM decay are intertwined, and that measurements of these processes in isolation may lead to incorrect estimates of the magnitude and source of C losses from soils.

Jacobs, Luke M.↗
DOE OSTI2013

Monitoring Uranium Transformations Determined by the Evolution of Biogeochemical Processes

Our contribution to the larger project (ANL) was the phylogenetic analysis of evolved communities capable of reducing metals including uranium. We previously reported structural shifts in microbial communities of microcosms constructed with inocula from uranium-contaminated sediment from the Field Research Center (FRC). Incubations were for up to eleven months and samples were taken from both the top and bottom of the sediment of duplicate microcosms incubated at room temperature anaerobically. The biological indices of the microcosm bacterial communities revealed that under strong selective force (e.g., sulfate and uranium) some populations became dominant and the community diversity appeared reduced. With the reduction of U(VI), bacterial community diversity appeared to recovere to its T0 level. Our clone library results revealed that some bacterial populations were persistent in the microcosms during the 11 month incubation period, while others became more abundant or less detectable in response to the prevailing environmental factors. According to the Ribosomal Database Project’s (RDP) Classifier tool, beta-Proteobacteria and Acidobacteria (e.g., Gp8) were highly abundant in the microcosms throughout the incubation period, whereas Desulfovibrio, a known sulfate-reducing Genus within which uranium reducing capabilities also reside, was substantially more abundant at early sampling times when sulfate and uranium were abundant, compared to at the end of the incubation period (11 months). We speculate that the decrease in abundance of Desulfovibrio with time was caused by consumption of sulfate and uranium during early stages of incubation. Interestingly, groups identified by the RDP as unclassified bacteria and unclassified Desulfobacteraceae responded to the selective forces differently. These two groups appeared to be more robust at the end of the incubation period when the strong initial selective force of sulfate and uranium was absent or diminished. The statistical community comparison with UniFrac indicated that early and late stage samples were evolved from the original inoculum. The RDP library comparison tool revealed that bacterial community populations shifted at statistically significant amounts according to time and space. For example, as mentioned above, early stage Desulfovibrio and Desulfobacteraceae abundances were significantly different from those where found at late incubation stage (P=0.01). Similarly, iron-oxidizing bacterium Thiobacillus was significantly more abundant at late sampling times. These results, combined with data from our colleagues were submitted to and accepted for publication in Environmental Science & Technology.

58 GEOSCIENCES↗
DOE OSTI2017

Chromium (VI) reduction in acetate- and molasses-amended natural media: empirical model development

Stimulating indigenous microbes to reduce heavy metals from highly toxic oxidized species to more benign reduced species is a promising groundwater remediation technique that has already seen successful field applications. Designing such a bio-remediation scheme requires a model incorporating the kinetics of nonlinear bio-geochemical interactions between multiple species. With this motivation, we performed a set of microcosm experiments in natural sediments and their indigenous pore water and microbes, generating simultaneous time series for concentrations of Cr(VI), an electron donor (both molasses and acetate were considered), and biomass. Molasses was found to undergo a rapid direct abiotic reaction which eliminated all Cr(VI) before any biomass had time to grow. This was not found in the acetate microcosms, and a distinct zero-order bio-reduction process was observed. Existing models were found inappropriate and a new set of three coupled governing equations representing these process dynamics were developed and their parameters calibrated against the time series from the acetate-amended microcosms. Cell suspension batch experiments were also performed to calibrate bio-reduction rates in the absence of electron donor and sediment. The donor used to initially grow the cells (molasses or acetate) was found not to impact the reduction rate constants in suspension, which were orders of magnitude larger than those explaining the natural media microcosm experiments. This suggests the limited utility of kinetics determined in suspension for remedial design. Scoping studies on the natural media microcosms were also performed, suggesting limited impact of foreign abiotic material and minimal effect of diffusion limitation in the vertical dimension. These analyses may be of independent value to future researchers.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Microbial communities biostimulated by ethanol during uranium (VI) bioremediation in contaminated sediment as shown by stable isotope probing

Stable isotope probing (SIP) was used to identify microbes stimulated by ethanol addition in microcosms containing two sediments collected from the bioremediation test zone at the US Department of Energy Oak Ridge site, TN, USA. One sample was highly bioreduced with ethanol while another was less reduced. Microcosms with the respective sediments were amended with 13C labeled ethanol and incubated for 7 days for SIP. Ethanol was rapidly converted to acetate within 24 h accompanied with the reduction of nitrate and sulfate. The accumulation of acetate persisted beyond the 7 d period. Aqueous U did not decline in the microcosm with the reduced sediment due to desorption of U but continuously declined in the less reduced sample. Microbial growth and concomitant 13 C-DNA production was detected when ethanol was exhausted and abundant acetate had accumulated in both microcosms. This coincided with U(VI) reduction in the less reduced sample. 13 C originating from ethanol was ultimately utilized for growth, either directly or indirectly, by the dominant microbial community members within 7 days of incubation. The microbial community was comprised predominantly of known denitrifiers, sulfate-reducing bacteria and iron (III) reducing bacteria including Desulfovibrio, Sphingomonas, Ferribacterium, Rhodanobacter, Geothrix, Thiobacillus and others, including the known U(VI)-reducing bacteria Acidovorax, Anaeromyxobacter, Desulfovibrio, Geobacter and Desulfosporosinus . As a result, the findings suggest that ethanol biostimulates the U(VI)-reducing microbial community by first serving as an electron donor for nitrate, sulfate, iron (III) and U(VI) reduction, and acetate which then functions as electron donor for U(VI) reduction and carbon source for microbial growth.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Influence of triethyl phosphate on phosphatase activity in shooting range soil: Isolation of a zinc-resistant bacterium with an acid phosphatase

Phosphatase-mediated hydrolysis of organic phosphate may be a viable means of stabilizing heavy metals via precipitation as a metal phosphate in bioremediation applications. We investigated the effect of triethyl phosphate (TEP) on soil microbial-phosphatase activity in a heavy-metal contaminated soil. Gaseous TEP has been used at subsurface sites for bioremediation of organic contaminants but not applied in heavy-metal contaminated areas. Little is known about how TEP affects microbial activity in soils and it is postulated that TEP can serve as a phosphate source in nutrient-poor groundwater and soil/sediments. Over a 3-week period, TEP amendment to microcosms containing heavy-metal contaminated soil resulted in increased activity of soil acid-phosphatase and repression of alkaline phosphatase, indicating a stimulatory effect on the microbial population. A soil-free enrichment of microorganisms adapted to heavy-metal and acidic conditions was derived from the TEP-amended soil microcosms using TEP as the sole phosphate source and the selected microbial consortium maintained a high acid-phosphatase activity with repression of alkaline phosphatase. Addition of 5 mM zinc to soil-free microcosms had little effect on acid phosphatase but inhibited alkaline phosphatase. One bacterial member from the consortium, identified as Burkholderia cepacia sp., expressed an acid-phosphatase activity uninhibited by high concentrations of zinc and produced a soluble, indigo pigment under phosphate limitation. The pigment was produced in a phosphate-free medium and was not produced in the presence of TEP or phosphate ion, indicative of purple acid-phosphatase types that are pressed by bioavailable phosphate. Finally, these results demonstrate that TEP amendment was bioavailable and increased overall phosphatase activity in both soil and soil-free microcosms supporting the possibility of positive outcomes in bioremediation applications.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Experimental evidence for the impact of soil viruses on carbon cycling during surface plant litter decomposition

To date, the potential impact of viral communities on biogeochemical cycles in soil has largely been inferred from correlational evidence, such as virus-driven changes in microbial abundances, viral auxiliary metabolic genes, and links with soil physiochemical properties. To more directly test the impact of soil viruses on carbon cycling during plant litter decomposition, we added concentrated viral community suspensions to complex litter decomposer communities in 40-day microcosm experiments. Microbial communities from two New Mexico alpine soils, Pajarito (PJ) and Santa Fe (SF), were inoculated onto grass litter on sand, and three treatments were applied in triplicate to each set of microcosms: addition of buffer (no added virus), live virus (+virus), or killed-virus (+killed-virus) fractions extracted from the same soil. Significant differences in respiration were observed between the +virus and +killed-virus treatments in the PJ, but not the SF microcosms. Bacterial and fungal community composition differed significantly by treatment in both PJ and SF microcosms. Combining data across both soils, viral addition altered links between bacterial and fungal diversity, dissolved organic carbon and total nitrogen. Overall, we demonstrate that increasing viral pressure in complex microbial communities can impact terrestrial biogeochemical cycling but is context-dependent.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

SPRUCE Deep Peat Microbial Diversity, CO2 and CH4 Production in Response to Nutrient, Temperature, and pH Treatments during Incubation Studies

This dataset contains the results of a microcosm incubation study on deep peat collected from the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experimental site within the Marcell Experimental Forest in northern Minnesota, USA in September 2014. Microcosms were monitored for carbon dioxide (CO2) and methane (CH4) production, and microbial community dynamics were assessed using quantitative polymerase chain reaction (qPCR) and amplicon sequencing. The experiment was designed with a full factorial design with elevated temperature, nitrogen (N), (P), and pH treatments was used with samples from each transect serving replicates. In all, 96 microcosms were constructed to account for the 16 treatment combinations (Nitrogen x Phosphorous x pH x temperature), 2 time points, and 3 replicates. Temperature treatments were 6 degrees C, to mimic the SPRUCE ambient plot temperatures, and 15 degrees C to mimic the SPRUCE +9 degrees C treatment. These data show that one year of deep peat warming, microbial community structure and abundance of bacterial, archaeal, fungal, and methanogenic populations showed strong vertical stratification across the peat depth profile yet no clear response to the temperature treatments (Kluber et al, 2020). In an effort to identify factors that may be limiting decomposition and microbial community change in deep peat, we conducted an anerobic microcosm incubation of deep peat (150-200 cm depth). This dataset contains one data file in comma-separate values (*.csv) format. Additional metadata are provided: a data dictionary and a file-level metadata file in comma-separate values (.csv) format and a user guide in PDF (*.pdf) format.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Oligotrophic wetland sediments susceptible to shifts in microbiomes and mercury cycling with dissolved organic matter addition

Recent advances have allowed for greater investigation into microbial regulation of mercury toxicity in the environment. In wetlands in particular, dissolved organic matter (DOM) may influence methylmercury (MeHg) production both through chemical interactions and through substrate effects on microbiomes. We conducted microcosm experiments in two disparate wetland environments (oligotrophic unvegetated and high-C vegetated sediments) to examine the impacts of plant leachate and inorganic mercury loadings (20 mg/L HgCl 2 ) on microbiomes and MeHg production in the St. Louis River Estuary. Our research reveals the greater relative capacity for mercury methylation in vegetated over unvegetated sediments. Further, our work shows how mercury cycling in oligotrophic unvegetated sediments may be susceptible to DOM inputs in the St. Louis River Estuary: unvegetated microcosms receiving leachate produced substantially more MeHg than unamended microcosms. We also demonstrate (1) changes in microbiome structure towards Clostridia , (2) metagenomic shifts toward fermentation, and (3) degradation of complex DOM; all of which coincide with elevated net MeHg production in unvegetated microcosms receiving leachate. Altogether, our work shows the influence of wetland vegetation in controlling MeHg production in the Great Lakes region and provides evidence that this may be due to both enhanced microbial activity as well as differences in microbiome composition.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2008

Effect of shadowing on survival of bacteria under conditions simulating the Martian atmosphere and UV radiation

Spacecraft-associated spores and four non-spore-forming bacterial isolates were prepared in Atacama Desert soil suspensions and tested both in solution and in a desiccated state to elucidate the shadowing effect of soil particulates on bacterial survival under simulated Martian atmospheric and UV irradiation conditions. All non-spore-forming cells that were prepared in nutrient-depleted, 0.2-μm-filtered desert soil (DSE) microcosms and desiccated for 75 days on aluminum died, whereas cells prepared similarly in 60-μm-filtered desert soil (DS) microcosms survived such conditions. Among the bacterial cells tested, Microbacterium schleiferi and Arthrobacter sp. exhibited elevated resistance to 254-nm UV irradiation (low-pressure Hg lamp), and their survival indices were comparable to those of DS- and DSE-associated Bacillus pumilus spores. Desiccated DSE-associated spores survived exposure to full Martian UV irradiation (200 to 400 nm) for 5 min and were only slightly affected by Martian atmospheric conditions in the absence of UV irradiation. Although prolonged UV irradiation (5 min to 12 h) killed substantial portions of the spores in DSE microcosms (~5- to 6-log reduction with Martian UV irradiation), dramatic survival of spores was apparent in DS-spore microcosms. The survival of soil-associated wild-type spores under Martian conditions could have repercussions for forward contamination of extraterrestrial environments, especially Mars.

Venkateswaran, Kasthuri↗
DOE OSTI2012

Soil solid phases effects on the proteomic analysis of Cupriavidus metallidurans CH34

Cupriavidus metallidurans CH34 is a completely sequenced soil-borne beta-proteobacterium with known genome and proteome. Comparative 2-D electrophoresis and protein mass spectrometry were used to compare the proteome of C. metallidurans CH34 from liquid culture and after incubation for 1, 3, and 12 days in microcosms containing quartz sand, kaolinite, montmorillonite, or an artificial soil. Results showed that proteome from liquid culture was similar to CH34 proteins extracted from sand and kaolinite, whereas the proteins extracted from artificial soil differed significantly and no proteins were detected from C. metallidurans CH34 incubated in the montmorillonite microcosms. Protein recovery decreased on prolonging incubation time in all microcosms. Mass spectrometry identification showed that the trend of lower recovery upon incubation time was independent on the putative function of protein. These results suggest that the soil solid phase influences the protein recovery and soil proteomic analysis and that distinction between protein recovery and protein expression in soil will be a challenging for soil proteomic researchers.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Reduced soil diazotroph diversity decreases nitrogen fixation rates, but depends on land management

Soil diazotrophs convert atmospheric nitrogen into plant-available ammonium through free-living nitrogen fixation (FLNF). This sustainable nitrogen source can reduce our dependence on synthetic fertilizer inputs in conventional agricultural systems. However, we know little about the effect of diazotroph diversity on FLNF, especially given that FLNF is intermediate within the broad-narrow functional spectrum. Here, we determined how management-mediated shifts in diazotroph diversity would impact their ecosystem function (FLNF) by quantifying diazotroph diversity across a long-term management gradient during and after the growing season. In addition to field observations, we leveraged the same management gradient to manipulate diversity in soil microcosms via chloroform fumigation exposure. In the field, diazotroph diversity was significantly higher after the growing season, and the biologically-based annual cropping system harbored the highest diazotroph diversity. However, perennial cropping systems maintained the highest FLNF despite lower diazotroph diversity, and both soil moisture and temperature were stronger predictors of FLNF. Based on these results, integrating diverse perennial crops into agricultural landscape could result in greater N from FLNF, particularly at the end of the growing season. When we reduced biodiversity in a manipulation experiment, the diversity-FLNF association was stronger than in the field experiment, suggesting that FLNF communities are not as functionally redundant as taxonomically ‘broad’ ecosystem functions. Here, the strength of diversity-FLNF correlation varied by previous land management. Diazotroph diversity better predicted FLNF in annual and forest soil microcosms, and microbial biomass carbon better predicted FLNF in perennial soil microcosms. Taken together, our results show that while diazotroph diversity influences FLNF, especially under extreme environmental disturbances, abiotic factors like soil moisture and temperature are stronger constraints on FLNF in the field.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Root carbon interation with soil minerals is dynamic, leaving a legacy of microbially derived residues

Minerals preserve the oldest most persistent soil carbon, and mineral characteristics appear to play a critical role in the formation of soil organic matter (SOM) associations. To test the hypothesis that carbon source and soil microorganisms also influence mineral-SOM associations, we incubated permeable minerals bags in soil microcosms with and without plants, in a 13CO2 labelling chamber. Mineral bags contained quartz, ferrihydrite, kaolinite, or native soil minerals isolated via density separation. Using 13C-NMR, FTICR-MS, and lipidomics, we traced plant-derived carbon onto minerals harvested from microcosms at three plant growth stages, characterizing total carbon, 13C enrichment, and SOM chemistry. While C accumulation was rapid and mineral-dependent, the accumulated amount was not significantly affected by the presence of plant roots. However, the rhizosphere did shape the chemistry of mineral-associated SOM. Minerals incubated in the rhizosphere were associated with a more diverse array of compounds with different C functional groups (carbonyl, aromatics, carbohydrates, lipids) than minerals incubated in a bulk soil control. These diverse rhizosphere-derived compounds may represent a “transient fraction” of mineral SOM, rapidly exchanging with mineral surfaces. Our results also suggest that many of the lipids which persist on minerals are microbially-derived with a large fraction of fungal lipids.

Rhizosphere, soil organic matter, grassland, 13C-N↗
DOE OSTI2018

Biotransformation of AFFF Component 6:2 Fluorotelomer Thioether Amido Sulfonate Generates 6:2 Fluorotelomer Thioether Carboxylate under Sulfate-Reducing Conditions

The fate of per- and polyfluoroalkyl substances (PFASs) in aqueous film-forming foams (AFFFs) under anaerobic conditions has not been well characterized, leaving major gaps in our understanding of PFAS fate and transformation at contaminated sites. In this study, the biotransformation of 6:2 fluorotelomer thioether amido sulfonate (6:2 FtTAoS), a component of several AFFF formulations, was investigated under sulfate-reducing conditions in microcosms inoculated with either pristine or AFFF-impacted solids. To identify the transformation products, we used high-resolution mass spectrometry and employed suspect-screening and nontargeted compound identification methods. These analyses demonstrated that 6:2 FtTAoS was transformed primarily to a stable polyfluoroalkyl compound, 6:2 fluorotelomer thioether propionate (6:2 FtTP). It did not undergo further reactions to produce the perfluoroalkyl carboxylates and fluorotelomer sulfonates and carboxylates that were observed during aerobic transformations. Here, the 6:2 FtTP was recalcitrant to biotransformation, indicating the stability of the thioether group under sulfate-reducing conditions. The total oxidizable precursor (TOP) assay was used to assess the presence of other PFASs. Although nearly all of the PFAS mass initially present was recovered from the pristine microcosms, only 67% of the initial PFAS mass was recovered from the contaminated microcosms, suggesting the formation of volatile biotransformation products or those that could not be detected by the TOP assay.

54 ENVIRONMENTAL SCIENCES↗