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

PRIORITY RESEARCH DIRECTION:BIOGEOCHEMISTRY IN EXTREME SUBSURFACE ENVIRONMENTSBiofilm dynamicsExperimental investigations of the mechanisms and rates of energy/electron transfer across themicrobe-mineral interface have been initiated. These processes need to be synthesized innumerical models to simulate biofilm dynamics in porous media coupled to extracellulargeochemical reactions such as sorption, precipitation, and redox alterations. Other microbialcommunity responses such as signaling and motility also should be modeled numerically tocapture the functioning of the biofilm as a whole as it interacts with its pore environment. In thisway, metabolic activities that take place at the cellular level can be extended via modeling to thebiofilm scale.We envision that the coupled in silico-biogeochemical models will be linked with nextgenerationpore-scale models for hydrodynamic flow, transport, and geochemical reactions (seeFigure 21). The objective is to simulate the interactions between the biotic and abiotic geochemicalcycles at increasingly larger spatial scales.Modeling efforts should build upon recent experimental investigations that assess molecularscalebiofilm processes utilizing Flat-Plate, Channel Flow (FPCF) reactors that contain mineralphases with a face that is mounted flush with the floor of a channel through which an aqueousphase is passed by the exposed mineral surface (Geesy and Mitchell 2007). The top of the FPCFcontains a window for microscopic viewing of the mineral surface without interrupting flow. Thesystem has been used in the past to determine the influence of mineral surface-associatedmicrobial activities on secondary mineral formation and the influence of mineralogical propertieson the behavior and activities of bacteria colonizing the mineral surface under well-definedhydrodynamic conditions (Neal et al. 2001, 2003). The aqueous phase effluent from the reactorcan be chemically and microbiologically analyzed (e.g., microarray analyses for communitystructure and activity) to assess dynamic transformations and metabolistic processes occurring onthe mineral surface. Solid phase transformations and metabolic processes can further bedeciphered using high-resolution surface interrogation methods such as X-ray microtomography(Holman et al. 1998, 1999; Hansel et al. 2005), auger electron spectroscopy (Geesey et al. 1996),X-ray photoelectron spectroscopy (Neal et al. 2004, 2001), Mössbauer spectroscopy (Dong et al.2003), and X-ray absorption spectroscopy (Benner et al. 2002; Gonzalez-Gil et al. 2005).Modeling efforts may also take advantage of recent advances in magnetic resonance microscopy(MRM) that has historically been used to define water behavior and movement through complexheterogeneous porous media at high spatial resolution (Callaghan 1991; Seymour et al. 2004,2007). The approach has been recently used to define the local density of biomass based onmagnetic relaxation and diffusion of the water molecules entrained in a microbial biofilm, andthe translational dynamics for water at the pore scale (i.e., m 2 -mm 2 range) (Seymour et al.2004, 2007). MRM offers the opportunity to experimentally follow and map new sites ofbiomass accumulation as a result of diffusion- and advection-controlled dissemination ofindividual cells through porous geological media. It also offers the opportunity to detect andfollow sloughing of cell aggregates and aggregate-induced plugging of flow paths (Geesey andMitchell 2007). In these applications, the distribution of protons associated with protein andpolysaccharide components of bacterial cells that accumulate in different flow paths can bedistinguished from those of surrounding water molecules, and used to map and follow biomassaccumulation in porous media (Seymour et al. 2004, 2007).Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems 151