Earth and Environmental Sciences, Department of

Experimental verifications of metabolic potential in deeply-sourced springs in western Turkey

Thu, 21 Feb 2013 06:00:00 GMT

Experimental verifications of metabolic potential in deeply-sourced springs in western Turkey This study investigated microbial metabolism in fault-associated cool and hydrothermal springs in western Turkey in an effort to bridge thermodynamic predictions of favorable metabolic pathways with observations in vitro and the presence of diagnostic functional genes. Doing so will help constrain the utility of calculations of Gibbs free energies of reaction as predictive tools for microbial ecology, aiding future studies investigating the habitability of astrobiological targets such as Mars or Europa. Modern-day serpentinization and related weathering processes occur in the subsurface of ophiolite-hosted spring systems in Turkey, prompting two exploratory field surveys of several springs in both northwest and southwest Turkey. Both hydrothermal activity and serpentinization provide a source of reduced compounds and are thought to be important for energy generation on early Earth, as well as other rocky planets. The geochemistry of spring fluids is impacted by both hydrothermal alteration and the weathering of ultramafic reservoir rocks, producing chemically distinct systems with a diverse suite of metabolic options. Cultivation of native microorganisms from sampled spring fluids in targeted growth media, in conjunction with taxonomic affiliations with known organisms based on 16SrRNA bacterial phylogeny, is used to assess the metabolic diversity in each system. These findings are compared with calculated Gibbs free energies of reaction for several chemosynthetic metabolic pathways to assess whether or not they are consistent with actual metabolic capacity. Nitrogen-cycling functional genes are detected and related to growth in targeted media. Evidence for partial denitrification within a biofilm supported by fluid discharging from an actively burning methane vent in the Tekirova ophiolite (Yanartaş, southwest Turkey) is substantiated by geochemical and isotopic evidence, as well as observations in culture and the presence of functional nitrogen-cycling genes, substantiating thermodynamic predictions that some exergonic metabolic pathways are utilized in situ. Data obtained on taxonomic relationships and observations in vitro of heterotrophic, thermophilic enrichment cultures from hot springs in northwest Turkey sheds new insight onto the functional diversity of fault-associated hydrothermal and cool spring systems. These findings support a correlation between thermodynamics and metabolic potential, though environmental factors (e.g. availability of organic carbon and nitrogen) may limit metabolic functioning in situ.

Merging Genomics, Transcriptomics and Geochemistry to Assess Nitrogen Cycling in Terrestrial Hot Springs

Thu, 21 Feb 2013 06:00:00 GMT

Merging Genomics, Transcriptomics and Geochemistry to Assess Nitrogen Cycling in Terrestrial Hot Springs A multi-faceted study was conducted to evaluate nitrogen cycling in Mound Spring and “Bison Pool,” two geochemically similar, alkaline hot springs of the Lower Geyser Basin in Yellowstone National Park. Downstream geochemical trends are supported by results of genomic and transcriptomic studies of Mound Spring and “Bison Pool” chemotrophic and phototrophic microbial communities. Nitrogen stable isotope trends of “Bison Pool” and Mound Spring biomass corroborate genomic and transcriptomic data and reflect topographically-driven differences in exogenous nitrogen input between the two hot springs. Results indicate that both chemotrophic and phototrophic communities at Mound Spring are genetically capable of fixing nitrogen, and nifH gene transcripts suggest downstream variability in nifH expression that may be a result of downstream changes in fluid chemistry and microbial community variation between sampling sites. Results of gene surveys targeting functional nitrification and denitrification genes indicate a marked difference between these processes at Mound Spring and “Bison Pool.” Nitrification potential is present only in the chemotrophic streamer biofilm communities at “Bison Pool,” yet the absence of amoA transcripts suggests that in situ nitrification was not occurring at the time of sampling. Genetic evidence of nitrification is absent from all Mound Spring chemotrophic and phototrophic communities sampled, and denitrification gene markers are relatively few. In contrast to Mound Spring, the microbial communities of “Bison Pool” appear to have widespread genetic capability of most denitrification processes, and the extensive presence of nirS gene sequences and transcripts suggests that nitrite reduction is an important metabolic process in the “Bison Pool” ecosystem.

Hydrological and Geochemical Characterization of a Restored Wetland in Central Illinois

Thu, 13 Dec 2012 06:00:00 GMT

Hydrological and Geochemical Characterization of a Restored Wetland in Central Illinois This research employed multiple isotopic and geochemical tracers to build on previous studies of a restored wetland at Hennepin and Hopper Lake in central Illinois. This study provides new hydrogen and oxygen isotopic data as well as major solute concentrations to elucidate both water inflow and mixing as well as biogeochemical processes. This study supports previous findings that groundwater is the principal water source, there is little hydrologic interaction between the Illinois River and the restored wetland, and geochemical processes in the wetland would support its use as a future contaminant sink.

Sulfur Speciation Analyses of Heated Soils using X-ray Absorption Near Edge Structure Spectroscopy

Mon, 10 Dec 2012 06:00:00 GMT

Sulfur Speciation Analyses of Heated Soils using X-ray Absorption Near Edge Structure Spectroscopy The determination of sulfur speciation changes in soils that result from wildfires is important for understanding the mobility of soil mercury (Hg), which is most strongly bound to reduced sulfur ligands. The transport of leached sulfate and Hg particulates to water bodies is enhanced after a fire as a result of increased susceptibility of soils to erosion, and could increase the production of toxic methyl mercury. X-ray absorption near-edge structure spectroscopy was used to measure the changes in sulfur speciation of soils collected from near Vallecito Reservoir (Durango, CO), an area affected by the 2002 Missionary Ridge wildfire. A soil sample from a burned area in this region was heated at 225°C for 120 min. Separate aliquots of another soil from an unburned area were heated in a muffle furnace for 120 min at 25, 150, 175, and 225°C, and at 225°C for 15, 30, and 345 min. In general, the fraction of sulfate increased by 71 to 209%, and the sulfoxide, reduced aliphatic sulfur, sulfonate, and sulfone fractions decreased by 80 to 98%, 55 to 91%, 40 to 49%, and 23 to 39%, respectively. The fraction of aromatic sulfur remained relatively unchanged. When changes in only the organic sulfur content were considered, the reduced aromatic sulfur content increased by 35 to 86%, while the sulfonate and sulfone content remained relatively the same at 21 to 25% and 5 to 6%, respectively. Sulfoxide and reduced aliphatic sulfur content decreased by 71 to 96% and 30 to 79%, respectively. The fractions of sulfite and sulfonium content were generally < 2% of the total sulfur. The apparent oxidation of reduced aliphatic sulfur due to heating suggests that mercury originally bound to these functional groups is likely released during a wildfire. Some mercury may persist, however, bound to reduced aromatic or aliphatic sulfur that remain in the soil or to weaker chemical functional groups in soil organic matter or minerals. Mercury(II) may therefore be more readily mobilized during precipitation events and, in addition to the increase in oxidized sulfur that provides a leachable source of sulfate, may possibly contribute to enhanced methylation in nearby surface waters.