Analysis of microbes encased in ancient, Antarctic ice

 

Co-Pis:   Paul Falkowski (IMCS, Rutgers University)

               Sang Hoon Lee (visiting microbiologist from the Polar Sciences Laboratory, Korean Oceanographic Research and Development Institute (KORDI)

 

            As part of a study to decipher Antarctic climate patterns, we have been collaborating with Dr. David Marchant (Dept. of Earth Sciences, Boston University) to examine buried ice in the Dry Valleys region of Antarctica.  Dr. Marchant is part of an NSF-funded Long-Term Ecological Research (LTER) project in the Dry Valleys region of the Transantarctic Mountains and kindly provided us with ice samples from both Mullins Valley and Beacon Valley for biological and chemical analyses. The ice samples provided to us were from two specific regions: Mullins valley (DLE-98-12) and upper Beacon Valley (EME-98-03) (Figure 1). An extensive geological analysis of this region, including the buried ice formations, has been performed and is presented elsewhere (Marchant et al. 2002; Sugden et al. 2002).  The minimum age of the ice, as determined by cosmogenic-nuclide exposure-age dating and 40Ar/39A analysis of in situ volcanic ash-fall deposits on the sediment cap are between 100,000 and 300,000 years (ky) for DLE-98-12, and 7 million years (myr) for EME-98-03.  To our knowledge, the latter is the oldest ice on Earth. Subsequent examination of ice crystallography and oxygen stable-isotope composition indicated that EME-98-03 is a remnant of the ancient basal glacier derived from an expansion of the adjacent Taylor glacier, and was preserved frozen during the entire age with no major reworking (Marchant et al. 2002; Sugden et al. 2002).  This ice has remained in its solid state for at least this time period, with no thawing events or exchange with the atmosphere.  Thus, multiple lines of geologic evidence suggest that the microorganisms encased in the ice of EME-98-03 and DLE-98-12 have been separated and preserved since the late Miocene and late Pleistocene, respectively.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


           

 

 

 

 

 

 

The two ices have markedly different chemistries and microbial compositions. High-molecular weight DNA was successfully extracted from the encased microbial communities and was detectable as a tight band, as opposed to a broad smear, following agarose gel electrophoresis (Figure 2A, lane 1).  This hints at remarkable DNA preservation over very long time periods and in spite of high cosmic ray exposure; this area of Antarctica receives among the highest amount of incoming cosmic radiation on the planet. A reconstruction of the encased bacterial community compositions using 16S rRNA libraries identified thirty distinct phylotypes with several demonstrating reduced phylogenetic similarity to the currently catalogued species.  This suggests dominance of relatively few, novel bacterial phylotypes.

Having these ice samples in our possession represents an unprecedented opportunity to examine ancient, secluded and preserved microbial communities on Earth and relate their biological, biogeochemical and genetic composition to a unique and well characterized geologic history.  We hypothesize that the in situ microbial communities have been "encased" in the ice in a senescent state over their respective time periods, calling into question their potential viability and genetic architecture, as well as its source and mechanism of seeding. The overarching objectives of this study are to characterize the metabolic state and genetic architecture of ice microbial populations.

Our specific goals are to: (a) examine the potential recovery of viable microbes from these ice samples, and (b) to sequence the microbial residual genomes.  These analyses will allow us to ascertain whether microorganisms remain metabolically active and perhaps viable, over variable geologic time periods and allow, for the first time, a comparison of functional genes in microbes that are over 7 million years old. Viability potentially permits extrapolation of microbial communities to sustain extended periods of dormancy (longer than a single Holocene ice age), and yet potentially "reinfect" the environment.  It further addresses the question as to whether microbes can traverse large areas of our solar system in association with comets.  Sequencing speaks directly to the tempo of evolution of microbes since mid-Miocene time, and to the source of the microbes that are preserved in the ice.  The funding requested here is primarily for sequencing of the microbial DNA in collaboration with TIGR.

 

 

Collaborators:

 

Dr. David R. Marchant (Dept. of Earth Sciences, Boston University)- Dr. Marchant is involved with a LTER project in Beacon and Mullins Valleys and was responsible for sampling the ice.  He has also performed extensive geological analysis of this region, including stratigraphy and dating.

Dr. Huiming Bao (Department of Geology & Geophysics, Louisiana State University)- Dr. Bao also has extensive experience working in the Antarctic Dry Valleys.  His expertise includes tracing the origin and source of chemical compounds (e.g, salts) found in Antarctic Dry Valley soils, using stable isotope anomalies.

 

Relevant publications:

 

MARCHANT, D. R. and others 2002. Formation of patterned ground and sublimation till over Miocene glacier ice in Beacon Valley, southern Victoria Land, Antarctica. GSA Bulletin 114: 718-730.

SUGDEN, D. E. and others 1995. Preservation of Miocene glacier ice in East Antarctica. Nature 376: 412-414.