Browsing by Author "Urschel, Matthew R."

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Carbon source preference in chemosynthetic hot spring communities
(2015-03) Urschel, Matthew R.; Kubo, Michael
Rates of dissolved inorganic carbon (DIC), formate, and acetate mineralization and assimilation were determined in 13 high temperature (>73Â°C) hot springs in Yellowstone National Park (YNP) in order to evaluate their relative importance in supporting microbial metabolism. While 9 of the hot spring communities exhibited rates of DIC assimilation that were greater than that of formate and acetate, 2 exhibited rates of formate and/or acetate assimilation that exceeded that of DIC assimilation. Overall rates of DIC, formate, and acetate mineralization and assimilation were positively correlated with spring pH but showed little correlation with temperature. Communities sampled from hot springs with similar geochemistry generally exhibited similar rates of substrate transformation which is consistent with similar community compositions springs with similar geochemistry as revealed by 16S rRNA gene tagged sequencing. Amendment of microcosms with low (Î¼M) amounts of formate suppressed DIC assimilation in short term (<45 min.) incubations, despite native DIC concentrations that exceeded that of added formate by 2 to 3 orders of magnitude. The concentration of added formate required to suppress DIC assimilation was similar to the affinity constant (Km) for formate transformation as determined by community kinetic assays. These results suggest that dominant chemoautotrophs in high temperature communities are facultatively autotrophic or mixotrophic, adapted to fluctuating nutrient availabilities, and are capable of taking advantage of energy-rich organic substrates when they become available.
Toward Better Genetically Encoded Sensors of Membrane Potential
(2016-03) Urschel, Matthew R.; Hamilton, Trinity L.; Roden, Eric E.; Boyd, Eric S.
Facultative autotrophs are abundant components of communities inhabiting geothermal springs. However, the influence of uptake kinetics and energetics on preference for substrates is not well understood in this group of organisms. Here, we report the isolation of a facultatively autotrophic crenarchaeote, strain CP80, from Cinder Pool (CP, 88.7°C, pH 4.0), Yellowstone National Park. The 16S rRNA gene sequence from CP80 is 98.8% identical to that from Thermoproteus uzonensis and is identical to the most abundant sequence identified in CP sediments. Strain CP80 reduces elemental sulfur (S8°) and demonstrates hydrogen (H2)-dependent autotrophic growth. H2-dependent autotrophic activity is suppressed by amendment with formate at a concentration in the range of 20–40 μM, similar to the affinity constant determined for formate utilization. Synthesis of a cell during growth with low concentrations of formate required 0.5 μJ compared to 2.5 μJ during autotrophic growth with H2. These results, coupled to data indicating greater C assimilation efficiency when grown with formate as compared to carbon dioxide, are consistent with preferential use of formate for energetic reasons. Collectively, these results provide new insights into the kinetic and energetic factors that influence the physiology and ecology of facultative autotrophs in high-temperature acidic environments.