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Permafrost is continuously frozen soil, sediment or bedrock and occupies
over 20% of Earth's land surface. Microbes that live in this environment
must survive subzero temperatures, low water activity, low energy and
resource availability, long-term exposure to gamma radiation and cell aging.
Several of these conditions appear to be similar to those on other astral
bodies making permafrost a useful model for studying microbial adaptation to
these stresses. Most of Earth's permafrost harbors at least some
prokaryotes that have retained viability over geological time periods and
when the temperature is raised increase or renew their physiological
activity. We examined microbial populations in both Arctic and Antarctic
permafrost by determining which microbes are detected in the permafrost DNA,
which are detected after the permafrost has been allowed to incubate a few
weeks at 10C and which are detected after isolation of viable cultures.
Arctic permafrost, some of which has been continuously frozen for up to 3-4
million years, has a relatively large microbial population while the
Antarctic has lesser numbers. Both permafrost DNA and culture approaches
detect high and low GC gram-positive bacteria and Proteobacteria, suggesting
that they are best adapted to this environment. Most of the isolates grow at
­2.5C and have as their nearest phylogenetic relative other strains from
cold environments. These observations suggest that adaptation to these
conditions is a phylogenetically conserved trait. We have selected two
Arctic isolates from ancient permafrost for genome sequencing, a
Psychrobacter strain and an Exiguobacterium strain, representatives of two
of the three most common groups present. The Psychrobacter genome is now
(essentially) closed and the Exiguobacterium genome is approaching high
draft status. We have begun both the genomic and proteomic analysis via
comparative genomics, microarrays and proteomics, especially examining up
and down regulated genes and gene products in response to temperature and
salt stresses.


(Special acknowledgement to team members at MSU, The Joint Genome Institute
and Univ. of Michigan for the portion of the Center¹s work summarized in
this presentation.)

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