The Invasion of the Deep-Sea Microbes

By Jack Farmer and Leslie Mullen,
NASA Astrobiology Institute

On the deep sea floor, along the margins of diverging plates of ocean crust,
communities of microscopic organisms live around hot volcanic vents. These
seafloor hydrothermal systems have probably existed on Earth since the
oceans first formed, more than four billion years ago. The microscopic life
around the vents may also have an ancient heritage — genetic comparisons
suggest that modern vent microbes are close kin to the earliest forms of
life on Earth. These regions are therefore of special interest to
astrobiologists, who study the geology, chemistry, and biology of
hydrothermal vents to better understand how Earth’s early biosphere emerged.

A team of scientists is presently using the deep sea submersible “Alvin” to
further study these important communities. Alvin has a depth range of 4500
meters (2.8 miles), and therefore gives scientists access to the deep,
high-pressure regions where these vents exist.

Arizona State University professors John Holloway and Peggy O’Day have
teamed with microbiologist Craig Cary from the University of Delaware for
this new study. They hope to learn more about how the biology of
hydrothermal vent communities may be affected by differences in vent
chemistry and mineralogy.

The team is exploring deep-sea vents located at a latitude of nine degrees
North of the equator, along a large seafloor mountain chain called the East
Pacific Rise.

Where hot water exits the seafloor, tube-like structures called “chimneys”
form. The chimneys expel dark clouds of sulfide minerals, giving them the
nickname “black smokers.” The expelled sulfur cools upon contact with
seawater, and adds to the size of the chimney structures over time – some
have reached heights in excess of 60 meters (about 200 feet).

Previous studies of seafloor vent fields have revealed the existence of a
wide variety of chimney types, each showing large differences in chemistry.
As the chimneys grow over time, their physical, chemical and mineralogical
properties change and create new habitats for life. But scientists still
know very little about how microbial organisms respond to these
environmental changes.

Using a newly designed sampling system, the scientists will collect some of
the smaller chimney structures. The team will also sample vent waters to
determine any chemical differences, and monitor how heat-loving microbes —
known as thermophiles — colonize actively forming vent surfaces.

By studying the succession of microbial species that colonize chimneys, the
team hopes to improve our understanding of how such processes may have
driven patterns of diversification in early vent environments. Studies of
vent chemistry will also provide basic information about how deep sea vent
processes may have affected the overall geochemical balance of the Earth’s
oceans and atmosphere during our planet’s history.

The scientists plan to use the collected information to design a new
experimental laboratory at ASU. This laboratory will simulate the broad
range of pressure and temperature conditions observed in natural vent
systems, and enable scientists to study how microbiology varies under these
conditions.