|
 by Dr. David Noever
1. Why study life in extreme
environments?
In addition to understanding fundamental biology here on Earth
and speculating on comparable limits in the universe, if unusual
characteristics in microbial metabolism can be identified and
studied, the transfer of this knowledge is almost immediate to
applications in environmental cleanup, pollution prevention,
or energy production.
Many researchers envision a range of medically, industrially,
and environmentally useful compounds derived from the extreme
heat-loving, or"hyperthermophilic" Archaea, as well
as antifreeze properties from cold-loving, or "cryophilic"
microbes.
Biomolecules from these organisms are active at temperatures
that generally degrade normal cellular molecules (or membranes),
such as enzymes, lipids, and nucleic acids.
return
to Life on the Edge story
2. What are some everyday
examples of microbial extremophiles?
Although very few may make the immediate association, the majority
of DNA and genetic science now owes a debt to the study of extremophile
microbes. The first Archaea-related products were enzymes called
DNA polymerases for the research market, that make possible the
sequencing or decoding of large blocks of all kinds of DNA.
As a simple example, the use of DNA evidence in criminal trials
for forensic experts would not be possible without the study
of extremophiles. A recent article in Time Magazine (Jan 11,
1999) reported that DNA analysis is used to match suspects to
evidence left at unsolved crime scenes at the astonishing rate
of cracking more than 500 otherwise mysterious crimes PER WEEK.
These numbers will only increase as analysis becomes more comprehensive
and database methods more sophisticated, in a modern day version
of fingerprint analysis.
The solving of more than 2,000 human genetic diseases, along
with the 200 more common diseases that may have therapeutic benefits
from understanding a patients genetic fingerprint, will in large
part hinge on the successful application of these very stable
DNA cutting enzymes originally found in the extremophiles, or
so called 'great bugs of fire'.
return
to Life on the Edge story
3. Who are the collaborators
working the project?
Life on the Edge is a collaborative educational project being
developed between NASA/Marshall Space Science Laboratory, the
Center for Astrophysical Research in Antarctica (CARA), and the
University of California White Mountain Research Station(WARS).
Participants include David Noever, Richard Hoover, Tony Phillips,
John Horack, and Dale Watring of NASA; Randy Landsberg of CARA;
and Joe Szewczak of the WMRS.
return
to Life on the Edge story
4. What do yeasts put in
snow have to do with Antarctica?
A fascinating example of yeasts, called Candida Antarctica, was
entered into the microbial collections around the beginning of
this decade [Aono R. Taxonomic distribution of alkali-tolerant
yeasts. Syst. Appl. Microbiol. 13: 394-397, 1990]. It is a landmark
case for a couple of reasons.
Its unusual tolerance for very basic environments (pH> 10
or more basic than strong household cleaning, ammonia solutions)
and extreme cold made it of sufficient interest to both scientists
and industry to file one of the earliest patents on a living
organism [U.S. Pat. 5,273,898].
The major interest commercially in the livelihood of this yeast
relies partly on effectively degrading fats and oils, with a
powerful enzyme called lipase. Many organisms and humans share
this breakdown pathway to digest fats and lipids, but the Antarctic
yeasts have evolved a particularly stable variety that allows
the cold breakdown of lipids. This particular strain was found
in Lake Vanda, Antarctica in 1990.
An interesting side note here is that one of the most active
areas of exploring for extremophile microbes is in the skeletons
of beached or dead whales in their naturally cold environments.
Whales and seals have a very slow decay rate, particularly in
polar regions and because of their very thick layers of blubber,
also spawn a community of bacteria that breakdown fats. A single
whale that had sunk to the bottom of the polar seas was recently
recommended for microbial analysis when a Russian rescue mission
discovered its presence while on a reconnaissance mission. This
find is considered important to developing new kinds of thermally
stable enzymes by standing watch both as biologist and vulture
in the carcass of naturally decaying polar life.
return
to Life on the Edge story
5. What do yeasts put in
snow have to do with archaea?
Nothing. Yeasts are eukaryotes, sharing the same superkingdom
as humans. Some of the already decoded genes of these yeasts
shed considerable insight into how human genes may work in health
and sickness.
But yeasts are extremophiles. The most historically significant
organism to Western civilization is arguably, Sacchyromyces,
because it allowed complex carbohydrates in grain to be fermented
to simpler sugars, breads and ethanol. The choice of Sacchyromyces
for the bulk of the Life on the Edge project was motivated by:
a) full genetic script is available for understanding the biological
mechanism underlying its cryosurvival, including its strategic
use of heat shock proteins. This organism remains one of the
elite half-dozen complete genetic scripts available.
b) logistically, a large and robust supply of industrially inexpensive
microbes
c) logistically, safety in handling and culturing, along with
provision of simple media for growth
d) many examples of extremophile strains, including a radiation
tolerant variety and the close relations between this organism
and the Candida Antarctica (both are allied yeast families which
share some metabolic pathways). Some more direct examples are
the radiation resistant and heat tolerant strains, such as one
candidate for further experiments, called Saccharomyces cerevisiae
Hansen, which can survive under intense 'cooking' ( Fingerhut
R et al. Cellular radiation effects and hyperthermia: cytokinetic
investigations with stationary phase yeast cells. Radiat. Environ.
Biophys. 18: 19-26, 1980).
return
to Life on the Edge story
6. What organisms would
be most representative of early Earth as we understand it?
This is an area of active research, depending on new fossil
evidence, geophysical records and even climatic models for atmospheric
conditions.
One survivor under similar conditions to what some expect to
finally find as the early Earth environment--archaea--an ancient
branch of microbial life on Earth was classified as the third
branch of the tree of life by scientists in 1977. Unlike the
better known bacteria and eukaryotes (plants and animals), many
of the archaea can thrive in extreme environments like volcanic
vents and acidic hot springs. Examples of these organisms can
live without sunlight or organic carbon as food, and instead
survive on sulfur, hydrogen, and other materials that normal
organisms can't metabolize.
If you want to get your own fascinating microbial zoo together,
search around the the major microbial collection banks, using
particular search terms such as extremophiles, barophilic, thermophilic,
radiation, acidic, alkaline, etc. and then by location like geyser,
volcano, etc.
ref: http://www.atcc.org/catalogs/catalogs.html
return
to Life on the Edge story
7. How does this
project relate to cutting edge research?
While biology has made tremendous (unprecedented) strides
in uncovering the genetic and environmental tricks for surviving
extreme environments, this area of biology remains a robust area
for phenomenology. Simply, do they survive? is an ongoing question,
allied particularly to 'where would they best survive?' While
the goals of the Life on the Edge project are modest and constrained
by the need to serve a large and diverse community of "Partners
in Discovery", there is considerable literature underlying
its basic scientific themes.
For example, to underscore the continued interest in this kind
of research, consider the following abstracts from the most recent
round of successful award grants given by the National Science
Foundation's Life in Extreme Environments (LeXEN) program:
"The experiments are conceptually very simple, and
technically require only routine microbiological and molecular
biology procedures. The experiments proposed will determine the
longevity of microorganisms entrapped in ice under different
environmental conditions"
ref: http://www.nsf.gov/cgi-bin/showaward?9714206
Or:
"The interior ice sheets of the continent of Antarctica
have always been assumed to be devoid of indigenous organisms.
While plants, protozoa, and bacteria are present at the fringes
of the continent, the combination of low temperatures, long periods
of darkness, and the absence of liquid water make the interior
extremely hostile to life. Further research will confirm whether
these microbes are indigenous to the Antarctic interior and investigate
their biology and ecology. The discovery of organisms capable
of survival in interior Antarctica would provide us with new
insight into the adaptability of life."
ref: http://www.nsf.gov/cgi-bin/showaward?9713990
return
to Life on the Edge story
8. Would aerobic or anaerobic
conditions be most representative of an extreme environment?
Some of the early tests organisms require oxygen and others
do not. Desulfurella acetivorans will be used as an anaerobic
microbe that was first identified thriving near a Russian volcano.
return
to Life on the Edge story
9. Will the "Life
on the Edge" microbes survive?
This is a major question that the first experiments will
seek to explore. If properly handled, most microbes can be successfully
freeze-dried and revived (a process called lyophilization). This
step in and of itself suggests that some kinds of protocols may
shed light on limits to survivability.
return
to Life on the Edge story
10. Why not use snow algae
or permafrost soil microbes for this experiment?
While fascinating in their own right, the diverse culturing
conditions make for some complications in scaling up to a larger
statistical sample. Recall that in the long history of microbiology,
only around 500 archaea have been grown as identified and classifiable
single cultures (monocultures have traditionally been a requirement
for putting in a microbial library). This 50 is a small fraction
of the millions of archaea so far unclassified, largely because
of in either obtaining or culturing them in typical laboratory
conditions (e.g. room temperature, atmospheric pressure, etc.).
By the nature of extremophiles, an extreme environment must be
duplicated for optimal growth.
return
to Life on the Edge story
11. Practically
speaking, can educators really do this experiment?
There are a host of reliable tests for microbial growth
that can be incorporated into the classroom protocol without
expensive equipment. Because these yeasts particularly produce
large amounts of carbon dioxide as they grow, there are simple
and safe monitoring techniques to score the viability after recovery
from an extreme environment for comparison with more innocuous
conditions.
return
to Life on the Edge story
12. What can we conclude
about the mechanisms of microbial survival?
Much of the ability to investigate mechanisms of biological
action, whether tailored antifreeze proteins or adaptive heat
shock proteins, the first step in that derives directly from
choosing a test organism that is both hardy and already possesses
a complete genetic script for comparison. It is expected that
the genetic code will be cracked in the future at the previously
unprecedented rate of one new microbe every 1-2 months, but even
that phenomenal rate of progress will yield a minute fraction
of the total Earth's diversity available for analysis (which
is literally estimated to be upwards of 40 billion species).
return
to Life on the Edge story
13. How can I participate
in Life on the Edge?
Join the NASA MSFC "Partners
in Discovery" program by electronic mail and follow
the progress of the White Mountain experiment. When recommendations
or actual samples are available, these partners will be notified
with regular updates.
return
to Life on the Edge story
14. What are the earliest
ancestors of modern life?
Relatively recent findings in the last 20 years holds
that there are three major families or branches on Earth's tree
of life. Depending originally on the presence of a cell nucleus,
a first division split the tree into two branches, called the
eukaryotes and prokaryotes. The prokaryotes are the bacteria,
while eukaryotes are the so-called higher forms of life, including
humans, plants and animals. When genetic comparisons became more
comprehensive, the third branch called archaea was decided to
be sufficiently different to qualify as an independent superkingdom
on Earth.
A major difference is that eukaryotes put their genes inside
a nucleus, while prokaryotes do not. In the archaea, there is
no nucleus, but many genes behave like those in higher organisms.
Archaea are thought to have a common ancestor with bacteria,
but billions of years ago the third domain, eukaryotes, broke
off from archaea, eventually developing into plants, animals
and us. Archaea include microbes that live at the extremes of
the planet - the very, very cold, hot or high-pressure places
that no other form of life could endure.
As such, archaea are the extremophiles who boldly thrive where
no other life form would go. Some scientists have suggested that
as such, archaea may represent the earliest form of life and
thus may be the most likely form of life existing on other planets.
About 500 species of archaea are now identified, but speculation
may not be far off in projecting that given the difficulties
of collecting and classifying them,there may be a million others.
The life form is thought to produce about 30 percent of the biomass
on Earth, much of it in the Antarctic Ocean.
In fact, as far back as 1994, Myrna Watanabe, a biotechnology
consultant, wrote that the existence of this third branch of
life "here on Earth has led scientists to realize that planets
they hitherto assumed to be lifeless might support life."
return
to Life on the Edge story
15. What was Earth like
3 to 4 billion years ago?
Little or no oxygen, higher sulfur and methane concentrations
either from volcanic activity or the primordial Venus-like atmosphere.
The lack of ozone in the upper reaches of the atmosphere allowed
a very high flux of ultraviolet radiation from the Sun to reach
any life exposed on the Earth's surface. Estimates of temperature
are a subject of great investigation currently, with some models
producing cyclical ice ages that periodically reset all but the
most robust forms of life to a near extinction level. This area
remains an important scientific topic for understanding both
the geological, climatic and ultimately biological history of
Earth.
return
to Life on the Edge story
16. Are there astrophysical
objects where life might exist?
Comets and meteors have captured recent attention as perhaps
having prebiotic but complex molecules that could serve as precursors
for later developments of carbon based life. The chemical sampling
of a comet serves as a future mission goal of a flight program
called StarDust, which will fly through the tail of a comet 5
years following its launch in February, 1999.
return
to Life on the Edge story
17. Are there planetary
or lunar objects where life might exist?
A fascinating field which has historically been considered
severely limited by a lack of evidence for water-ice, but which
increasingly has received reexamination both because of new experiments
and space missions and because of a widening limit to where biologists
expect to find life on Earth. This remains a statistical sample
of one.
return
to Life on the Edge story |
Join our growing list of subscribers - sign
up for our express news delivery and you will receive
a mail message every time we post a new story!!!
Headlines