Some of the world’s tiniest organisms may have a large
impact on climate change.
(July 13, 2015) Researchers
from the U.S. Department of Energy’s Argonne National Laboratory and the
University of Tennessee found that microorganisms called archaea living in
marine sediments use completely novel enzymes to break down organic matter into
carbon dioxide.
These single-celled archaea eat organic carbon in marine
sediments. Enzymes in the archaea break down large carbon molecules into
smaller units. This process releases carbon dioxide and methane into the water
and eventually, into the atmosphere.
However, as the temperature of oceans and bodies of
freshwater increases, this carbon cycling process accelerates. The temperature
at the bottom of the ocean, for example, is approximately two to four degrees
Celsius (35 to 39 degrees Fahrenheit). According to Andrzej Joachimiak, Argonne
distinguished fellow and director of the Structural Biology Center, if the
ocean temperature rises one or two degrees, the rate of carbon release might
increase.
“About 40 percent of Earth’s organic carbon is stored in
marine sediments,” Joachimiak said. “An increase in temperature and
acceleration of the carbon cycling process in these sediments is a major
concern.”
Joachimiak said scientists are uncertain about how fast
archaea process carbon and whether the release is accelerating. Once
researchers have these statistics, they may find ways to better predict the
environment’s response to a changing climate.
This understanding starts at the molecular level. Using
resources at the Advanced Photon Source, a DOE Office of Science User Facility,
and the Advanced Protein Characterization Facility, the research team produced
and crystallized bathyaminopeptidase, or BAP – one of the enzymes found in the
archaea – to look into its structure and observe how it operates. They found
that BAP plays an important role in breaking down proteins and, consequently,
the turnover of atmospheric carbon.
The biggest challenge the researchers had was determining
BAP’s function, because no previously cultured organisms shared a close
ancestry. These types of organisms are considered microbial “dark matter”
because their physiologies are unknown and they have never been grown in a lab.
And because it is difficult to study their physiologies,
scientists cannot determine their precise impact on ecosystems and major global
events. For example, BAP was found to be structurally similar to the known
amino acid ester hydrolase, but had evolved to serve an entirely different
function.