by Karin Valentine
A chimney structure from the Sea Cliff hydrothermal vent field
more than 8,800 feet (2,700 meters) below the sea's surface
submarine boundary of the Pacific and Gorda tectonic plates.
by Ocean Exploration Trust
In the strange, dark world of the ocean floor, underwater fissures,
called hydrothermal vents, host complex communities of life.
These vents belch
scorching hot fluids into extremely cold seawater, creating the
chemical forces necessary for the small organisms that inhabit this
extreme environment to live.
In a newly published study, biogeoscientists
Jeffrey Dick and
Everett Shock have determined that specific hydrothermal
seafloor environments provide a unique habitat where certain
organisms can thrive.
In so doing, they have
opened up new possibilities for life in the dark at the bottom of
oceans on Earth, as well as throughout the solar system.
have been published in the
Journal of Geophysical Research - Biogeosciences.
On land, when organisms get energy out of the food they eat, they do
so through a process called cellular respiration, where there is an
intake of oxygen and the release of carbon dioxide.
the molecules in our food are unstable in the presence of oxygen,
and it is that instability that is harnessed by our cells to grow
and reproduce, a process called biosynthesis.
But for organisms living on the seafloor, the conditions for life
are dramatically different.
"On land, in the
oxygen-rich atmosphere of Earth, it is familiar to many people
that making the molecules of life requires energy," said
co-author Shock of Arizona State University's
School of Earth and Space Exploration
School of Molecular Sciences.
contrast, around hydrothermal vents on the seafloor, hot fluids
mix with extremely cold seawater to produce conditions where
making the molecules of life releases energy."
In deep-sea microbial
ecosystems, organisms thrive near vents where hydrothermal fluid
mixes with ambient seawater.
Previous research led by Shock
found that the biosynthesis of basic cellular building blocks, like
amino acids and sugars, is particularly favorable in areas where the
vents are composed of ultramafic rock (igneous and meta-igneous
rocks with very low silica content), because these rocks produce the
Besides basic building blocks like amino acids and sugars, cells
need to form larger molecules, or polymers, also known as
Proteins are the most
abundant of these molecules in cells, and the polymerization
reaction (where small molecules combine to produce a larger
biomolecule) itself requires energy in almost all conceivable
"In other words,
where there is life, there is water, but water needs to be
driven out of the system for polymerization to become
favorable," said lead author Dick, who was a postdoctoral
scholar at ASU when this research began and who is currently a
geochemistry researcher in the School of Geosciences and
Info-Physics at Central South University in Changsha, China.
"So, there are two
opposing energy flows: release of energy by biosynthesis of
basic building blocks, and the energy required for
What Dick and Shock
wanted to know is what happens when you add them up: Do you get
proteins whose overall synthesis is actually favorable in the mixing
They approached this problem by using a unique combination of theory
From the theoretical side, they used a thermodynamic model for the
proteins, called "group additivity," which accounts for the specific
amino acids in protein sequences as well as the polymerization
For the data, they used
all the protein sequences in an entire genome of a well-studied vent
By running the calculations, they were able to show that the overall
synthesis of almost all the proteins in the genome releases energy
in the mixing zone of an ultramafic-hosted vent at the temperature
where this organism grows the fastest, at around 185º Fahrenheit
By contrast, in a
different vent system that produces less hydrogen (a basalt-hosted
system), the synthesis of proteins is not favorable.
provides a new perspective on not only biochemistry but also
ecology because it suggests that certain groups of organisms are
inherently more favored in specific hydrothermal environments,"
studies have found that methanogens, of which Methanocaldococcus
jannaschii is one representative, are more abundant in
ultramafic-hosted vent systems than in basalt-hosted systems.
energetics of protein synthesis in ultramafic-hosted systems are
consistent with that distribution."
For next steps, Dick and
Shock are looking at ways to use these energetic calculations across
the tree of life, which they hope will provide a firmer link between
geochemistry and genome evolution.
"As we explore, we're
reminded time and again that we should never equate where we
live as what is habitable to life," Shock said.