Recent advances in nanotechnology and analytic
instrumentation allow biogeochemical processes between
microbes, metals and minerals to be probed at remarkable
levels of complexity, sensitivity, space and time. One of the
dominant trends in geomicrobiology is the detailed
characterization and application of biogenic minerals whose
characteristic features are at the nanometer scale in at least one
dimension. It is therefore important to understand β and
ultimately exploit β the unique properties and behavior of a
wide range of nanoscale biogenic materials. Central to this
trend are the development and application of effective analytic
techniques for characterizing the structural and chemical
properties of biogenic minerals with (sub)nanometer spatial
resolution.
Microbes in the subsurface are involved, directly or
indirectly, in a plethora of activities such as metal reduction
and oxidation, mineral precipitation and dissolution. These
innate capacities of subsurface microbes are often exploited
for in situ remediation of contaminated sites. During
subsurface bioremediation of uranium-contaminated sites,
indigenous metal and sulfate-reducing bacteria may produce
biogenic minerals such as mackinawite (FeS) which could
potentially drive abiotic uranium reduction.
In this work, the propensity of well-characterized biogenic
mackinawite to abiotically reduce U(VI) was tested using a
suite of electron microscopy and synchrotron based
spectroscopy techniques. High-resolution electron microscopy
confirmed the formation of nanoparticulate uraninite [UO2] on
the surface of biogenic mackinawite, which was further
confirmed with bulk X-ray absorption spectroscopy that
revealed the molecular coordination environment of uraninite.
X-ray photoelectron spectroscopy confirms that U(IV)
reduction was coupled to the oxidation of S2-
and not structural
Fe(II) within the biogenic mackinawite. The combination of
rigorous nano- and bulk-scale characterization provides
insights into such biogeochemical processes, that occur during
subsurface biostimulation, that are not always possible with
bulk-scale analyses alone