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BRIE is designed to encourage interdisciplanry research in the area of
biogeochemistry. Below is a summary of the research that is currently being
performed by the BRIE-BEMR Group.
Amy Barnes (Ph.D. student, Materials Science and Engineering)
(Much of the work discussed here has been performed with
the assistance of several other researchers, including Laura Liermann and
Brigitta
Kalinowski)
Hornblende
is an important source of calcium and magnesium in soil solutions and also contains a high
content of trace elements (e.g. Fe, Mn, Mo, V etc.) needed by soil microorganisms for
survival. Iron is of particular interest to our group because of its low solubility
and availability in aerobic environments at neutral pH. Microorganisms require iron
as an important constituent in the respiratory pathway and also for enzyme
functions.
Hornblende mineral was collected from Gore Mountain in the Adirondacks,
NY. Two bacteria were also isolated from the hornblende-rich soil of Gore
Mountain. These bacteria were chosen because of their ability to vigorously grow in
the presence of hornblende. The two bacteria were determined to be a streptomycete
of the genus Streptomyces and an arthrobacter, most likely of the genus Arthrobacter,
though neither of the 16s rRNA gene sequences matched sequences in the Ribosomal Database
Project database. The honblende mineral for these experiments contains a high
concentration of secondary phases. In order to use a homogenous, reproducible sample
for our experiments, a glass of similar bulk composition was fabricated from raw materials
to test in parallel with the honblende mineral.
A wide variety of experiments have been performed with the crystalline
hornblende mineral (HBM) and the hornblende glass analog (HBG) with both of these
bacteria. A micro-electrode with a tip radius of 0.6mm and vertical resolution on
the order of 0.3 mm measured the pH gradient that developed within the biofilm during
stagnant growth. Also, the change in surface composition after incubation for
various amounts of time was also examined using x-ray photoelectron spectroscopy
(XPS).
Heather Buss (Undergraduate
student, Geosciences)
Laura Liest (Undergraduate
student, Geosciences)
We will be investigating the uptake of Molybdenum in the
common nitrogen-fixing bacteria Azotobacter vinelandii. Molybdenum is an
essential component of the nitrogenase protein used in reducing atmospheric nitrogen (N2)
to its biologically-useable form ammonia (NH3). Because Mo has been shown
to limit the productivity of nitrogen-fixing bacteria, and is available in ultratrace
quantities in most environments, we would like to better understand how the bacteria
acquire Mo from their environment. We will be culturing A. vinelandii in mediums
with different rock types commonly found in soils including granite and basalt. These rock
types contain different amounts of Mo, and we expect to see higher A. vinelandii
growth rates on the Mo rich rocks. We will analyze Mo release rates of the rocks in the
presence and absence of A. vinelandii. We expect that A. vinelandii
produces an organic chelator for Mo similar to the siderophores it produces to acquire Fe
from the nitrogenase protein. The ligand increases the Fe release rate from hornblende and
we expect similar results for Mo. The rocks, culture mediums, and bacteria will be
analyzed for isotopic fractionation by multi-collector ICP-MS. We hypothesize that, as in
most biological systems, lighter isotopes are preferentially taken up by organisms
resulting in an isotopic "fingerprint" of biological activity. There has been
little documentation of Mo fractionation through biological activity to date.
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