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> Home > Faculty
& Staff > Dr. Gill Geesey
Biological Elemental Sulfur Reduction. Sulfur is a ubiquitous
element in thermal areas of Yellowstone National Park. A casual examination
of many thermal features in the Park reveals a white-to-yellow-colored material
coating the surfaces of springs, pools and soils that is most likely elemental
sulfur. While much is know about the formation of elemental sulfur through
chemical and biological reactions, little is known about the fate of elemental
sulfur in these extreme environments. Our research focuses on the use
of elemental sulfur as a substrate for anaerobic respiration by thermophilic
archaea in Dragon Spring in the Norris Geyser Basin. Two archaea in the
kingdom Chrenarcheota have been isolated from sulfur flocs deposited at the
source of Dragon Spring as a result of abiotic oxidation of hydrogen sulfide
gas in the source water upon exposure to the atmosphere. In the laboratory,
these Chrenarchaeal isolates use the sulfur flocs as a terminal electron acceptor
during growth on complex organic carbon compounds such as pine needle extract,
peptone, tryptone, or yeast extract, producing hydrogen sulfide as a product
of respiration. The isolates appear to be well adapted to the spring environment
with an optimum temperature and pH for growth close to that which exist in
the source water. One important question related to elemental sulfur
reduction that remains to be resolved is how these microbes transfer electrons
from their cell surface to the solid phase sulfur.
Interestingly, these Chrenarchaeal isolates are not detected in water and floc
samples from Dragon Spring by polymerase chain reaction-based molecular methods
using domain-specific archaeal or bacterial primers. They are detected, however
in other nearby springs and elsewhere in the Park. Current research involves
the construction of isolate-specific primers and fluorescently-labeled oligonucleotide
probes for detection of these isolates in Dragon Spring.
Microbial Mats as a Pathway for Bioaccumulation of Monomethyl-Mercury
in a Thermal Area Aquatic Food Web. Mercury (Hg) occurs naturally
in various forms in the soil and water of thermal areas of Yellowstone National
Park. Hg(II) in spring water is transformed to monomethylated Hg (MeHg) by
microbial populations associated with mats of Zygogonium, a red alga in a
number of acidic springs within the Park. Our research has found that
larvae of a soldier fly species (Diptera:Stratiomyidae) selective graze specific
populations of several algae within the mat community. This grazing
behavior results in elevated levels of MeHg in the gut and tissues of the
larvae. Future research will be directed to the investigation of further
biomagnification of MeHg in avian populations in the area that feed on the
insect larvae, and identification and characterization of the microorganisms
that mediate the methylation reaction.
Graduate student Eric Boyd at the Geesey lab sample site
Current Lab Personnel:
Eric Boyd, Ph.D. Student
Trevor Beard, Undergraduate Student
Will Leavitt, Undergraduate Student
Robert Jackson, Technical Support Staff
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