Unique Habitat Found Inside Earth Posted on July 25th
Researchers
studying life in the deep subsurface of our planet have discovered a unique
bacterium living 1 mile (1.7 km) below the Earth’s surface. The tiny bacteria live in a
community of subsurface microbes inhabiting a South African platinum mine.
The deep
subsurface of Earth harbors many
unique microbes that are only accessible through large scale drilling
projects or mining. By trekking into the ultra-deep mines of South
Africa, researchers are getting a rare glimpse into this unique habitat. In
the depths of South Africa’s Northam Platinum mine, scientists from the University of Western Ontario and Princeton University have gained access to many previously
undiscovered microbial communities.
While
mining and drilling allow scientists to sample the unique environment below the
Earth’s soil, these activities obviously disturb the subsurface of the planet.
Digging into the ground disrupts the microbial communities that live there.
When people enter mines and caves, they bring with them a massive number of
non-native microbes. Because of this, it’s difficult to get uncontaminated
samples.
The team
from the recent study decided to test samples from mines in order to determine
just how contaminated they really are. They collected samples from slime, or biofilm, growing on
the walls of the Northam mine in South Africa. An explosion of life occurs
where subsurface water leaks out of the mine walls and meets with oxygen,
leading to films of microscopic organisms.
Previously,
researchers overlooked these biofilms because they thought the films would be
too heavily contaminated. To test this theory, the team determined whether or
not their biofilms were formed by contaminant organisms from the surface, or by
unique subsurface organisms.
The study,
by Greg Wanger, Tullis Onstott and Gordon Southam, was published in a recent
edition of the journal Geobiology.
The authors
showed that the biofilms contained a number of unique organisms associated with
the deep subsurface, and therefore such films might be an excellent place to
search for new and unusual species of microbes. In fact, in their study the
team came across one particularly strange microbe shaped like a tiny,
microscopic star.
Shaping
up bacteria
Microbes
come in a number of shapes and sizes, but most of these shapes are rather
uncomplicated. The easiest shape for a microbe to make is a sphere. Like a soap
bubble, the cell membranes of microbes tend to naturally form this simple
structure due to forces such as surface tension.
According
to the research team, “the diversity of all bacterial shapes is more
difficult to explain.” Other shapes often seen in microbes include rods
and spirals, but these take a bit of extra work on the part of the microbe. To
make more complicated shapes, microbes have to use extra energy to fight
against the natural forces that favor the sphere. According to the research
team, the biofilms from Northam mine “contained a morphologically diverse
assortment of bacteria.”
Some rare
microbes go beyond the common and form radically unique shapes. The microbe
discovered in the depths of the Northam mine is one such microbe. Using
high-powered microscopes, the team captured images that show star-shaped cells
with four to nine points. It’s a unique structure for a microbe and one that has
not been witnessed before.
So why
would a microbe want to take the shape of a star?
As living
organisms, every microbe
needs food. When we need food, we can simply pick it up and put it in our
mouths. That’s not the case for most microbes. Many microbes simply float about
in their environment in the hope that they’ll be able to absorb the nutrients
they need to survive
Many
microbes “eat” by letting nutrients diffuse through their cell
membrane. A sphere may be easy to form, but it doesn’t provide the largest
surface area for a cell. By forming a more complicated shape, with a cell wall
that folds and bends, the surface area of the cell is increased in relation to
its interior volume. This means there’s more cell wall through with the microbe
can absorb its food.
The new
microbe discovered by the researchers in South Africa has likely developed its
unique shape in response to its unique environment. The deep subsurface of the
planet is thought to be quite “nutrient poor” there’s not a lot of
food to go around. Microbes need to develop clever strategies to out-compete
their neighbors. The surface-area-to-volume ratio for the star-shaped cells is
thought to be as much as ten times better than common bacteria like e. coli.
This advantage may help the stars survive amidst a neighborhood of microbes
competing for the same food.
Inside
planets
Scientists
are just beginning to understand the unique types of life beneath the surface
of our planet. Astrobiologists
are particularly interested in the subsurface because it can help them
understand how microbes might survive deep beneath the topsoil of other
planets.
Upcoming
and current missions to search for signs of past or present life on Mars are
focusing on life beneath the martian soil. Right now, NASA’s Phoenix
Lander is using a scoop to dig on Mars. Recent images returned from Phoenix are already revealing clues about subsurface ice on the red planet.
The
European Space Agency’s ExoMars
rover may take the exploration of Mars’ subsurface one step further. Current
plans are to place a drill on ExoMars that could allow the rover to dig up to
12 feet.
NASA has also been developing prototype drills for use by
human explorers on Mars. Drilling technologies have already been tested by NASA
researchers in extreme environments on Earth, including the Canadian high
arctic.
Microbes
use many methods to survive in the nutrient-poor, oxygen-free, pitch-black
world deep beneath our feet. Studying these microbes might provide clues about
how organisms could live in harsh environments on other planets like Mars.
Because of this, unique microbes like the “stars” of Northam mine may
shed a bit of light on the future of planetary exploration.