4.1. ASTROBIO – Formation of the Solar System

By | July 6, 2014
4.1. ASTROBIO - Formation of the Solar System

[BLANK_AUDIO] How has life managed to survive over three
billion years on the earth and what Adaptation does it need to survive
environmental Changes throughout its long tenure on the
Earth? Well, one of the best ways to answer this
question is to go And look at how life manages to survive
and grow in extreme environments. Well, what do we mean by extreme? Some people think that it's a very
anthropocentric Term, it's just a matter of taste. What may be extreme to one organism, is
not extreme to another. But we think that there is something much
more fundamental to it than that. Biological systems, do only function in a
continual, particular, physical And chemical extreme, and as we go to
these circle Of extremes, such as high temperature, low
temperature, increased pressure, We find that the diversity of life
generally in these environments Tends to decrease. So it does seem that there are real
extremes. Extremes beyond which life cannot go. Boundaries to the biosphere that are Determined by physical and chemical
extremities. And studying the organisms at these
extremities can tell us much, about How life on earth has managed to cope,
with conditions on our planet. And, just as interestingly, whether life
might be Able to cope with the physical and
chemical extremes To be found on other planetary bodies. The organisms that inhabit these extreme
environments we call extremophiles. Literally, extreme lovers. There mainly the prokaryotes, the bacteria
and alkali that we saw in the Tree of life, but there are Some eukaryotes that live in extreme
environments. Even flies for example, that live at the
edges of volcanic hot Springs in Yellowstone National Park, but
by and large, once we get to Really great extremes on the Earth, we
find that The organism that's are inhabiting these
environment are the prokaryotes.

What are the types of extreme environments
that exist out there? Well these are some of the environments
we'll look at in a little more detail. There are hot and cold places, there are
places that are very salty or Very dry, there are also places that are
very acidic or very alkaline or Basic, and there are also places With intense pressure and also intense
radiation. Let's have a look to begin with at hot
environments. There are many hot environments on the
Earth that harbor Life, a good example is deep sea
hydrothermal vents; places Where reduced fluids containing sulfates,
other toxic chemicals are spewing Out from the crust of the Earth into the
oceans. And these hydrothermal Vents can be producing water, well over
100 degrees Centigrade because of the high pressure in
the deep oceans. The organisms that inhabit these hot
environments, which also include volcanic Hot springs in places like Yellowstone
National Park, are called thermophiles, If they grow between 50 and 80 degrees, or
if they Grow at really high temperatures above 80
degrees, they're called hyperthermophiles. Now it's important To remember that these organisms aren't
just capable of growing At these temperatures, they actually need
to grow at high temperatures. If you take a hyperthermophile, for Example, whose optimum growth temperature
is above 80 degrees, and you bring it down to room
temperature, it will generally die. These are microbes that actually have to Be growing at these very high
temperatures. A good example is methanopyrus kandleri.
This is An archea that inhabits black smokers,
deep ocean Hydrothermal vents that are black, because
they're producing sulfites, Minerals that are produced in the oceans
as These fluids gush out of these black
smoker vents. The organism can grow up to temperatures
of 110 degrees centigrade. Some of the challenges it faces like all Thermophiles or hyperthermophiles are the
breakdown of biomolecules.

Those high temperatures impart Energies to, the, to the microorganisms. They tend to cause the biomolecules to
breakdown. They also have a problem with membrane
fluidity. Very high temperatures, the energy causes
the Membranes to start shaking apart almost
quite literally, And that fluidity in the membrane can
cause Problems for the integrity of the cell
membrane. How does it deal with these challenges With living in these high temperature
environments? Well two of the ways that deals with This is by evolving thermostable proteins
and enzymes. Enzymes being biological catalysts
involved in Carrying out chemical reactions in the
cell. These proteins have extra chemical bonds
and other types of Features that maintain their stability at
these very high temperatures. It turns out that these proteins, or
catalysts, These enzymes have, have commercial uses
as well. For example, thermostable catalyst enzymes
are used in biological washing powder. One of the reasons why your washing powder
can work at high temperatures is because It contains proteins, enzymes form
microorganisms that have Been isolated from hydrothermal springs,
volcanic hot springs. So you see we can use these thermostable
enzymes And proteins for some very prosaic, but
commercially useful applications. Other adaptations include changes to the
cell membranes and composition To allow those membranes to maintain
stability at high temperatures. Microorganisms have also been found in
freezing environments, Such as the depths of Antarctic ice
sheets. This is an example of the deep lake in the
Antarctic lake called Vostok. And just above that lake are
microorganisms in The ice, in the accretion ice that forms
above That deeply buried lake. In these sorts of ice sheets,
microorganisms Adapted to cold conditions can grow, and

Are called psychrophiles, microorganisms
that can grow At temperatures at less than 15 degrees
centigrade. What are the challenges of living in a
cold environment? Well, one challenge of course is membrane
damage from ice. If ice crystals form in the cell, it can
damage the membranes. Another problem is decreased membrane
fluidity. In very cold temperatures, the lipids
begin to solidify, a bit like if You put butter in your fridge, it begins
to get a lot more solid. Those fatty acids, those lipids in the
cell Membranes, begin to solidify at very cold
temperatures, and Reduce the fluidity of the membrane that's
necessary For the cell to export materials and
import nutrients. Another obvious Problem in freezing environments is the
availability of liquid Water, much of it is frozen up in ice. And so, organisms can have trouble getting
hold of the Liquid water that they need to carry out
by chemical reactions. So how is it that these microbes can adapt
to these extremely cold conditions? Well one way in which they adapt is by
altering their membrane composition. A bit like the microbes living at High temperatures, they need to change the
composition Of the membranes to maintain their
fluidity at low temperatures. One way in which they can do this is To incorporate more unsaturated fatty
acids into their membranes. These unsaturated fatty acids have kinks
in the membrane structure that pulls, Pushes apart the membrane and makes it
more fluid under cold conditions. Some of these microbes and other organisms Also have antifreeze agents such as
sugars. And these sugars prevent ice crystals from
forming in The cells and reduce the chances of ice
crystals Forming and damaging the membranes,
another way in which They can circumvent problems of growing at
very low temperatures. So that's hot and cold environments. What about salty and dry environments?

Well, microorganisms have been found that
can inhabit very Salty environments, such as microbes that
live in the Dead Sea, and in deposits of salts around
the Dead Sea. These are called halophiles. And these halophiles, literally salt
lovers, can Grow at salt concentrations between 15 and
37%. Microbes that live in deserts, also
capable of Tolerating very dry conditions, and these
are called xerophilic Microbes, you can find them in the deserts
of The Atacama, the Sahara and other dry and
desiccated Environments of the earth. The challenges of living in salty and dry
conditions are actually quite similar. One problem is osmotic pressure and water
availability. In very high salt concentrations the salt
has the tendency to Pull water out of the cells by the process
of osmosis. So cells have a problem in hanging onto
their liquid water. And, of course, in dry deserts the problem
is also the water tends to evaporate. Which causes problems for the maintenance
of water in The cell, also osmotic effects in very dry
conditions. Another challenge faced by mi-, microbes
in Both salty and dry environments is
membrane integrity. Maintaining the integrity of the membranes
and preventing them from falling Apart under these very high salt Concentrations that tend to disrupt
biomolecules. And under very dry conditions, where the
dry conditions also tend To cause disruption to the membranes lack
of water. How do organisms adapt to these very
extreme, salty, and dry conditions? Well two ways they can adapt are to
control water loss from the cells. They can produce salts and other solutes
within the cell that tend to hang Onto the water, make it more difficult for
it to dissipate from the cell. Another way in which they can deal with
these extreme conditions is To go into a state of dormancy. When they're dormant, they're not active,
but it Allows them to wait around until
conditions improve.

There's a particular case for microbes
living in deserts where They may want to go dormant and wait until
liquid water Becomes available and they can reproduce
and grow again, and Then go into a stage of dormancy when it
dries up. Microbes have also been found that live at
extremes of pH. For example the Rio Tinto River in Spain
whose pH is down to 0.4 high concentration of protons in the
water makes it very, very acidic. There are also places with very high pH, Such as Mono Lake in the United States
that Has a pH up to 12.5 very alkaline Or basic environments, that pose great
challenges to microbes. The challenges that are faced to the
organisms that live in these environments Include the breakdown of their cellular
components. For example, in acidic environments the
very high proton concentration that's Responsible for that acidity can disrupt Biomolecules, causing them to become
inoperative. These very challenging pH conditions are Also a great challenge to metabolic
processes. Processes for gaining energy and carrying
out chemical reactions inside the cell. How the cells Adapt to these extreme pHs? Well, one way they can adapt is to
regulate the PH inside the cell in order to make it
neutral. So for example, a microorganism living in
very acidic environments will Pump out protons from the cell and
maintain the inside the Cell at near neutral pH, and at neutral pH
the biomolecules Are much more stable and metabolic
processes can proceed without disruption. In other words, These cells really don't like to be in an
acidic environment. But they can change their internal
conditions Such they can survive and grow in acidic Environments without the acid on the
outside of The cell affecting cellular reactions
inside the cell. This is a really ingenious way by which
cells can survive and grow in

Acidic conditions and similar sorts of
processes Are also found in very alkaline
environments. Organisms have also adapted to life under
high pressure. In fact many of the habitats on earth for
life are actually at high pressure. Two examples are the deep oceans, and the
deep crust of the earth. In the deep oceans many of the trenches
are at great depths, such as The Mariana Trench at 11 kilometers depth, And here pressures exceed a thousand
atmospheres. The microbes that can live in these Environments are called piezophiles
microbes, literally pressure Loving microbes. In fact at the current time we don't know
what upper pressure limit for life Is, but certainly they can survive at high Pressures we found in these deep ocean
trenches. Microbes are also found in the deep crust
living In rocks kilometers underneath the surface
of the Earth. The challenges of living at high pressure
are the pressures cause the Tight packing of molecules and a loss of
fluidity in cell membranes. Pressure can also cause impaired cellular
functions in activities. Particularly of enzymes that are necessary
to carry out The catalytic functions of chemical
reactions, inside the cell. How do cells, how do organisms adapt to
live in These high-pressure environments in the
deep oceans or in the crust? Well, one way in which they can adapt is
by changing gene expression. They can produce, for example, molecules
that enhance the uptake Of nutrients and other elements that they
need for growth across the Cell membrane and thereby adapt to These challenging environments under high
pressure. They can also change their membrane
structure. For example, by introducing unsaturated
fatty acids To increase membrane fluidity under high
pressures. And you'll notice, that unsaturated fatty
acids were also The way in which microbes can adapt to low
temperatures. So some of the mechanisms that organisms
use to adapt

To one extreme are also used to adapt to
other extremes. They can be common responses to different
environmental extremes. We might think about one of the most
extreme environments known to man and that Is the conditions of outer space.
Can microorganisms survive in outer space? Space is characterized by extremes of Radiation, freezing temperatures,
dessication, and no oxygen. A few years ago, my own laboratory
launched rocks into orbit, and these rocks Were bolted onto the outside of the
International Space Station. And we brought some back to earth a year
and A half later to see whether anything had
survived in space. And we found a single micro organism, a
gloeocapsa, Which is a type, cyanobacterium, a
photosynthetic micro organism That was capable of surviving in the
extreme conditions Of space for a full year and a half. Of course it didn't grow in space, but it
did survive. These types of experiments Show how outer space is an environment That can even be survived by some
microorganisms. Showing how hardy they are and how able
they are to Resist environmental extremes, if only for
a short length of time. Many extremes that we find on the earth
don't occur in isolation. I've talked about high and low
temperatures, I've talked about salty environments, and
highly acidic, And alkaline environments, but in fact in Many natural environments there are
frequently multiple extremes. An astrobiologist are very interested in Polyextremophiles, extremophiles that can
tolerate multiple extremes. Here's just one example of a rather famous
organism Called deinococcus radiodurans. This is a microbe that can tolerate high
levels of radiation, it's also Found in environments with cold
temperatures, it's Found in deserts that are very dry. Some of these organisms can tolerate
vacuum conditions, and members of this Group, the deinococci, are also found in
very acidic environments as well.

So we see how there are polyextremophiles
that can survive multiple Extremes, and by studying these
microorganisms, We can get better understandings of how Microbes tolerate the boundaries of
extremes, to Find the boundaries of the earth
biosphere. Why is this of any interest to
astrobiologists? Well, there are really two reasons why
we're interested in studying Microbes at extremes, and particularly
those Microbes that can tolerate multiple
extremes. First of all, of course, it tells us about
the boundaries of the earth's biosphere. What are the limits Of life on earth?
When do we go beyond those limits? And how might environmental changes
throughout the history Of the Earth, even if environmental
changes cause By humans, affect life on earth, and those Microorganisms that inhabit the outer
boundaries of the biosphere? But the other reasons for being interested In studying life in extreme environments
is Because it might give us better ideas About the habitability of other worlds
such as Mars, Europa, and Enceladus and Titan and Other planetary bodies of interest to
astrobiologists. Once we know the physical conditions on
those planetary bodies, we want To be able to assess whether they are
within the boundaries for life. Whether life might be able to persist on
those planetary bodies. The only way in which we can do that is by Studying microorganisms of life in general
in extreme environments, and seeing Whether extremes we observe on other
planetary bodies are extremes that Can be tolerated by life forms that we
know on the Earth. So the study of life in extreme
environments is essential For assessing habitability, the ability
other planetary bodies to harbor life. So what have we learnt in this lecture? We've learnt that extremophiles are
organisms That tolerate or require physical and

Chemical extremes in order to be able to
survive and grow and reproduce. We've learnt that, although extremophiles
span all major domains of Life, most of them come from the
prokaryotes bacteria in [UNKNOWN]. We've learned that adaptations to extreme
conditions Sustain cell integrity and function,
frequently via modifications To the cell membrane and molecules such As proteins and enzymes, catalytic
molecules in cells. We've learned that interactions between
multiple Extremes may influence extremophile growth
and survival. The study of life in extreme environments Is pivotal to understanding the emergence
of Life on the Earth and understanding the Boundaries for life in the universe at
large. And finally we've also learned that
molecules isolated From extremophiles may also have
commercial and industrial use. [BLANK_AUDIO]