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RESEARCH STATEMENT
The principle focus of my
research projects are the activity and survival of bacteria and other
microorganisms in the deep subsurface (> 0.5 km) and their impact on the
geochemistry and mineralogy of their environment. Among the questions we
attempt to address are: 1) How do subsurface microorganisms evolve by adaptation
or selection or horizontal gene transfer? 2) What constrains the diversity
and density of microorganisms? 3) What role does radiation play as an energy
source for life? 4) Could life have originated in the subsurface? 5) What
methods can be adapted to test for life in the Martian subsurface?
These projects have been
and continue to be field-based and require a multi-disciplinary,
multi-institutional approach. Field measurements, sample acquisition,
laboratory analyses and publication of results by geochemists,
microbiologists and molecular biologists have to be highly coordinated in
order for the questions above to be addressed.
Currently we are involved
in two field projects, the first situated in the Canadian Arctic and the
second sited in the world’s deepest mines in South Africa. Both projects seek
to address fundamental scientific question regarding bacteria/rock
interactions while at the same time developing applications of this
information that will benefit mankind. We are also involved with educational
outreach efforts for the South African project focusing on previously
disadvantaged, postgraduate students in South
Africa and black American students in the U.S.
Indiana-Princeton-Tennessee
Astrobiology Institute (IPTAI)
During the past two years
IPTAI has established a Mars
analog site in the Canadian arctic where we can access through mines and
boreholes deep permafrost. This region of Canada is unique in that it provides
ready access to rock/permafrost in Archean metavolcanic and metasedimentary
strata, permafrost that extends to a depth of 400-500 meters, much like is
anticipated on Mars. Currently we are working with the Finish Geological
Survey, the Univ. of Toronto and the Univ. of Waterloo
to profile the microbial diversity, density and activity and the permafrost
and subpermafrost saline water transition and we are learning how to
successfully drill down to this region and install downhole
instrumentation. Graduate student Dan McGown has
been developing approaches to extract large DNA fragments for metagenome
sequencing from these sites. The entire genome for an uncultured sulfate
reducing bacteria that dominates the South African sites below 2.5 km has
just been completed. All three of these aspects are vital to any planned
mission to Mars that will attempt to search for life in the subsurface. Postdoc John Kessler has been developing instrumentation
for analyses of CH4 isotopic composition using field portable
laser spectrometers that we hope will eventually be flown to Mars to identify
the source of the CH4 that has been detected there by telescopic
searches. This gas may be a signature of martian
subsurface life and characterization of its isotopic composition is essential
to the future of the Mars exploration program. On Earth such devices will
revolutionize our understanding of global carbon cycles and greenhouse gas
inputs.
The NELSAM Project
This project builds upon
the data gathered in the Witwatersrand Deep
Microbiology Project that ran from 1998 to 2006 and described in more
detail below. The NELSAM project funded
by the Tectonics and Geodynamics Program at NSF has enabled us to establish
an under ground laboratory (URL) for investigating the relationship between
tectonic processes and microbial activity. The URL is located at a depth of
3.8 km in quartzite within the seismically active Pretorious fault zone. Four
boreholes have been cored across this fault zone, two for the installation of
geophysical instruments to record fault displacements, one for the analyses
of gases released during seismic events and the fourth (known as DAFBIO) to
record changes in the fluid chemistry and microbiology associated with
seismic events. Installing these boreholes at this depth and remote from the
access shafts and into rock with an ambient temperature of 60oC has
not been easy and has required 2 years of concerted. The cores collected
during drilling of the 40 m long DAFBIO hole are currently being processed
for DNA and 35SO4 activity. The borehole has been
imaged and fracture zones identified and soon a specially designed packer
will be installed to isolate water weeping fractures. Using this packer we
will be able to conduct in situ microbial activity experiments to test the
long term activity of the indigenous thermophilic microorganisms. Grad student,
Mark Davidson has been designing and performing experiments using
thermophilic sulfate reducing bacteria that are similar to the dominant
microorganism in the South African deep subsurface and these experiments are
being used to design the experiments that will be performed at the URL.
The Witwatersrand
Deep Microbiology Project
Due to the expense and
contamination associated with coring from the surface, few microbial rock and
water samples have been collected from depths greater than 0.5 kilometers.
These few samples, nevertheless have demonstrated that microbial communities
do exist in a variety of subsurface rocks and sediments down to 2.8
kilometers below the surface (kmbls.). Conditions in the deep subsurface
approach the limits for life and novel "extremophiles" have been
isolated from these environments. Investigations of deep, terrestrial
environments also offer great potential for gaining insights into potential
exobiological niches and into how microorganisms can adapt to and survive in
relatively harsh environments. The extreme conditions encountered in the
subsurface include excesses in temperature, pressure, salinity, and ambient
radiation, and the low availability of energy sources and liquid H2O.
The paucity of high quality samples, however, has greatly hindered efforts to
determine the size, structure, and metabolic activities of the deep
subsurface microbial communities and the biogeochemical processes that
support them.
Many fundamental
questions remain to be answered regarding the relationship between subsurface
microbial community dynamics and biogeochemical and hydrological processes.
- Does primary production of
organic substrates by autotrophic microorganisms dominate in certain
subsurface terrestrial environments over heterotrophic utilization of
organic substrates originally produced by surface-based photosynthesis?
This question has been hotly contested in the recent literature.
- What are the abiotic mechanisms and rates for H2 and
C1-4 production in the subsurface and are they sufficient to support
chemolithotrophic microbial communities? Radiolytic reactions have been
proposed as a source of H2 and abiotic
redox reactions involving water, inorganic C and mineral-bound Fe(II) have been proposed as sources of H2,
CH4 and light hydrocarbons.
- Are in situ microbial
activities so low as to only support average doubling times on the order
of centuries? Phelps et al. (1994) proposed this on the basis of
geochemical modeling, which yielded rates that were 103-106
lower than laboratory measurements. In situ measurements at high
temperature and pressure analogous to those performed at deep-sea vents
have not been undertaken. If true, have subsurface microorganisms
evolved special agents to guard against the deleterious environmental
effects, such as ambient radiation?
- A fracture flow hydrogeological regime dominates most terrestrial
deep subsurface settings. Are the deep subsurface microbial communities
present in fluid-filled fractures distinct from those embedded in the
rock strata? Are they responsible for the precipitation of
fracture-filling minerals? Because coring such environments from the
surface utilizes high pressure drilling fluids, which invariably
contaminates the fracture surfaces and adjacent rock matrix these
questions have not been appropriately addressed. Expensive packer
systems are also required to isolate discrete fracture zones for fluid
sampling to avoid mixing and contamination. Microbial colonization of
the deep subsurface occurs primarily by microbial transport through
fractures, particularly when topographically or hydrothermally-driven
meteoric water flow and fracture-generated permeability is enhanced by
tectonics. Consequently, difference between fracture and rock matrix
microbial communities may reflect differences in their residence time.\
These questions will
never be resolved with the collection of one core from a single site or a set
of rock or water samples from one mine. Rather, the distribution, diversity
and activity of microbial communities in a subsurface environment must be
examined in terms of a hydrogeologically and
geochemically well-characterized location by a sustained effort over several
years.
To overcome this
deficiency, we investigated the potential for the ultradeep
Au mines of South Africa
to provide unique "windows" into the deep, continental biosphere
through which a detailed analysis of microbial communities as a function of
various environmental parameters could be performed. The depths and pressures
of these mines approach those at ocean ridges and the temperatures of the
mined formations lie within the zone for microbial thermophilicity
(45-70oC). The microbial communities encountered in these mines
are composed of a mixture of contaminating (allochthonous)
and indigenous (autochthonous) microorganisms. To distinguish autochthonous
from allochthonous microorganisms we developed
sample collection and processing techniques that quantified and minimized the
allochthonous bacterial contaminants in the mine
samples. This permits evaluation of the relationship between the indigenous
microbial communities and large-scale hydrogeochemical
facies as well as small scale geochemical heterogeneity.
Thanks to the support
from the NSF LExEn (Life in Extreme Environments) Program, we are developing
the ultradeep mines in South Africa into a Long-term
Site for Interdisciplinary Studies into subsurface microbiology. This
facility will be comprised of an on-site laboratory with access to multiple
mines in S. Africa. With the collaboration
of South Africa’s
mining industry and academic institutions this site will be able to offer the
following attributes.
- The rock formations
encountered by the deep Au mines are representative of most terrestrial cratonic environments and include dolomite, mafic to siliceous lava, quartzite and shale. The
deep Pt mines occur in a 2.05 Ga basic to
ultramafic, hypabyssal intrusive providing an
environment similar to the ocean crust and the Martian subsurface.
- The hydrogeological
environment is a fracture flow regime similar to most deep, hard rock
settings. Rock cores from fracture zones bearing "
fracture " water at high temperature and pressure can be
obtained by side-wall coring. This type of sampling permits for the first
time to study the microbial communities and biomineralization processes
occurring in the low permeability rock matrix versus those of the
fluid-filled fracture.
- These mines are sufficiently
deep (>3.0 kmbls.) to yield thermophiles
having enormous biotechnological potential from rock samples and "fracture"
water with temperatures ranging up to 75oC. These mines are
the deepest on earth and plans for still deeper mining are underway.
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