Basic Research Needs for Geosciences - Energetics Meetings and ...

PRIORITY RESEARCH DIRECTION:BIOGEOCHEMISTRY IN EXTREME SUBSURFACE ENVIRONMENTSphases such as metal oxides (Fe and Mn), carbonates, and phosphates that are strongly reactivewith trace constituents both through surface and bulk substitution reactions.The biogeochemistry of natural extreme environments, such as thermal springs, oceanic ventsalong spreading centers, and deep, hot, geologic formations, has been investigated to provideinsights on bioadaptive processes and functions under stressful conditions. Subsurface microbeshave remarkable adaptability and ability to flourish in and extract energy from a variety ofapparently stark, lithotrophic environments. Extremophilic organisms exhibit diverse chemicalfunction and mediate complex geochemical reactions that influence pore water chemistry, thechemical and physical nature of reactive surfaces, and the composition of newly-formed solidphases that function as repositories for trace species. These reactions and processes can differmarkedly from those occurring under ambient conditions because of temperature, kinetic, and/orspecific organism effects. An important general observation for understanding this research areais that organism diversity (e.g., number of different species) greatly decreases as theenvironmental conditions become more extreme.Given this background, four critically important fundamental science challenges can bearticulated as follows:1. How do characteristic, deep, low-diversity subsurface microbial communities (e.g., probablygram-positive dominated) evolve in response to parameter changes resulting from energy usesuch as inoculation by near-surface organisms and increases in radiation, temperature,hydrogen, and carbon dioxide? Do evolved organisms and/or communities have greater orlesser effects on system geochemistry and minor element (e.g., radionuclide), speciation,biogeochemistry, and migration potential? These observations will inform more fundamentalstudies at smaller scale.2. What are the reaction rates and products of important biogeochemical reactions underrelevant conditions as function of organism type, population, and metabolic rate? How arethese moderated or controlled by coupled parallel or sequential abiotic reactions(precipitation, dissolution, surface complexation) with associated bulk mineral phases orreactive interfaces?3. What are the molecular processes, mechanisms, and biostructures that occur on or near thecell surface of extremophiles that influence metal/radionuclide speciation via electron orother chemical transfers, that precipitate trace or major element biomineral phases, or thatalter solid surfaces?4. Can new biogeochemical models for single cell and biofilm scales be conceptualized andformulated to: integrate complex intracellular biochemical pathways, biodirected reactions atthe cell surface, and extracellular, nonlinear abiotic reaction networks; improve coupledprocess understanding; quantify biologic-geochemical interdependencies and feedbackrelationships?Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems 147