ORNL researchers studied how the proteins of a bacterium named C. obsidiansis responded to different carbon sources. The microorganism (pictured growing on crystalline cellulose) could play a role in the development of a cheaper biofuel production process. Image credit: Jennifer Morrell-Falvey/ORNL |
Studies
of bacteria first found in Yellowstone’s hot springs are furthering
efforts at the Department of Energy’s BioEnergy Science Center toward
commercially viable ethanol production from crops such as switchgrass.
The
current production of ethanol relies on the use of expensive enzymes
that break down complex plant materials to yield sugars that are
fermented into ethanol. One suggested cheaper alternative is
consolidated bioprocessing, a streamlined process that uses
microorganisms to break down the resistant biomass.
“Consolidated
bioprocessing is like a one-pot mix,” said Oak Ridge National
Laboratory’s Richard Giannone, coauthor on a BESC proteomics study that
looked at one microorganism candidate. “You want to throw plant material
into a pot with the microorganism and allow it to degrade the material
and produce ethanol at the same time.”
The BESC study focused on Caldicellulosiruptor obsidiansis,
a naturally occurring bacterium discovered by BESC scientists in a
Yellowstone National Park hot spring. The microorganism, which thrives
at extremely high temperatures, breaks down organic material such as
sticks and leaves in its natural environment, and scientists hope to
transfer this capability to biofuel production tanks.
In a paper featured on the cover of the Journal of Proteome Research, the BESC team conducted a comparative analysis of proteins from C. obsidiansis
grown on four different carbon sources, ranging from a simple sugar to
more complex substrates such as pure cellulose and finally to
switchgrass. The succession of carbon substrates allowed researchers to
compare how the organism processes increasingly complex materials.
“This
progression helps us look at how proteins change given different carbon
substrates,” Giannone said. “One of the goals is to identify new
proteins that we haven’t seen before. If an unknown protein doesn’t show
up on the simple sugars or cellulose, but it shows up on the
switchgrass, then we can say something about that gene or protein—that
it responds to something the switchgrass is providing.”
The
researchers found that growth on switchgrass prompted the organism to
express an expanded set of proteins that deal specifically with the
hemicellulose content of the plant, including hemicellulose-targeted
glycosidases and extracellular solute-binding proteins. Acting together,
these two sub-systems work to break down the plant material and import
the resulting sugars into the cell. The scientists went on to show that
once inside the cell, the organism “switches on” certain enzymes
involved in pentose metabolism in order to further process these
hemicellulose-derived sugars into usable energy.
“By comparing how C. obsidiansis
reacted to switchgrass, relative to pure cellulose, we were able to
pinpoint the specific proteins and enzymes that are important to plant
cell wall deconstruction—a major roadblock to the production of advanced
biofuels,” Giannone said.
The team’s measurement of the full complement and abundance of C. obsidiansis
proteins, called proteomics, can now be combined with other
technologies such as genomics, transcriptomics and metabolomics in order
to obtain a 360-degree, system-wide view of the organism. Instead of
studying discrete proteins, these systems biology-type approaches
provide more thorough insight into the day-to-day operations of
bioenergy-relevant organisms and thus better equip researchers to make
recommendations about their use in ethanol production.
“One
goal for us at the BioEnergy Science Center is to take these ‘omic’
technologies and integrate the data so we can draw definitive
conclusions about a system,” Giannone said.
Coauthors
on the paper are Hamburg University of Technology’s Adriane Lochner and
Garabed Antranikian, and ORNL’s Martin Keller, David Graham and Robert
Hettich.
