| Abstract
| - Understanding how microorganisms influence the physicaland chemical properties of the subsurface is hinderedby our inability to observe microbial dynamics in real timeand with high spatial resolution. Here, we investigatethe use of noninvasive geophysical methods to monitorbiomineralization at the laboratory scale during stimulatedsulfate reduction under dynamic flow conditions. Alterationsin sediment characteristics resulting from microbe-mediatedsulfide mineral precipitation were concomitant withchanges in complex resistivity and acoustic wave propagationsignatures. The sequestration of zinc and iron in insolublesulfides led to alterations in the ability of the pore fluidto conduct electrical charge and of the saturated sedimentsto dissipate acoustic energy. These changes resulteddirectly from the nucleation, growth, and development ofnanoparticulate precipitates along grain surfaces and withinthe pore space. Scanning and transmission electronmicroscopy (SEM and TEM) confirmed the sulfides to beassociated with cell surfaces, with precipitates ranging fromaggregates of individual 3−5 nm nanocrystals to largerassemblages of up to 10−20 μm in diameter. Anomalies inthe geophysical data reflected the distribution of mineralprecipitates and biomass over space and time, with temporalvariations in the signals corresponding to changes in theaggregation state of the nanocrystalline sulfides. These resultssuggest the potential for using geophysical techniquesto image certain subsurface biogeochemical processes,such as those accompanying the bioremediation of metal-contaminated aquifers.
|
