Biofuel pays for itself with goods made from waste
DOE/Sandia National
Laboratories
EDITOR’S NOTE: Yet another example of scientific
research that may never reach fruition under Trump. Unless this methodology is
given to the oil industry, it is unlikely that the Energy Department led by
oil-controlled Rick Perry will allow this research to continue.
A recent discovery by Sandia
National Laboratories researchers may unlock the potential of biofuel waste --
and ultimately make biofuels competitive with petroleum.
Fuel made from plants
is much more expensive than petroleum, but one way to decrease the cost would
be to sell products made from lignin, the plant waste left over from biofuel
production.
Lignin typically is
either burned to produce electricity or left unused in piles because no one has
yet determined how to convert it into useful products, such as renewable
plastics, fabrics, nylon and adhesives.
The electricity isn't
even available to the general public; it's only used by companies that create
large amounts of lignin, like pulp and paper manufacturers.
Now Sandia scientists,
working with researchers from Lawrence Berkeley National Laboratory at the
Joint BioEnergy Institute, have decoded the structure and behavior of LigM, an
enzyme that breaks down molecules derived from lignin.
The group's work on LigM appears in the latest issue of the Proceedings of the National Academy of Sciences. The enzyme has little in common with other, better understood proteins, which previously made it impossible for scientists to guess how it functions.
This paper marks the
first time anyone has solved the structure of LigM, opening a path toward new
molecules and new, marketable products.
Revealing nature's closely-guarded secrets
For decades,
scientists have wrestled with the problem of breaking down lignin, the part of
plant cell walls that provides structure and protection from bacterial and
insect attacks. This strength also makes lignin difficult to deconstruct,
though there have been recent breakthroughs.
The plant matter used
to produce ethanol can be chemically or physically pre-treated so that the
lignin is deconstructed in the process.
However, these methods
can be expensive and reduce the amount of biofuel that can be harvested. They
could also interfere with later-stage lignin harvesting. That's why some
researchers are focused on finding enzymes that convert lignin naturally and
gently.
Sandia scientist and
lead author Amanda Kohler said her team knew enzymes could metabolize lignin
and its derivatives because there are decades-old records of bacteria using
enzymes for this purpose.
Sphingonomas bacteria
was discovered living in the waste water of a pulp mill more than 30 years ago.
Once researchers realized the bacterium's unique enzymatic pathways enabled it
to live on lignin, their challenge was then to understand the enzymes in these
pathways so they could mimic what nature had already done, and use that
understanding productively.
Enzymatic pathway to profit
Kohler and her team
focused on LigM, an enzyme used by Sphingomonas, because it performs a key step
in the conversion of lignin derivatives and it is the simplest of the known
enzyme systems that perform this function. "When trying to mimic natural
systems in a laboratory setting, the simplest, most direct systems are the
best," Kohler explained.
The team found that
half of LigM's structure is composed of a common protein architecture found in
all forms of life, from bacteria to humans. The rest of the enzyme -- the
active portion -- is not found in any other known protein structure. This
unique structure gives LigM the ability to bind specifically to molecules
derived from lignin.
"Solving the
structure allows us to understand how the organism may have evolved its unique
function, which I think is scientifically one of the most interesting
findings," said paper co-author and Sandia scientist Ken Sale.
The team used the Advanced
Light Source Synchrotron at Lawrence Berkeley National Laboratories, along with
high-performance computing and fundamental biochemistry to gain their insights
into LigM.
LigM is designed to
break down lignin derivatives, not lignin itself. It is important to understand
that LigM's function is only one key step in a longer pathway of reactions
needed to fully deconstruct lignin.
One active area of
research involves finding other organisms, possibly fungi, that can execute the
first step of breaking down large lignin mass into smaller fragments. Some of
the Sandia scientists who solved LigM's structure, Sale and Matthew Mills, have
recently learned more about another enzyme that helps drive the breakdown of
lignin into smaller fragments.
LigM works on a later
stage in the process, when smaller lignin fragments already have been converted
into a molecule called vanillic acid. "There is still work to be done to
figure out the whole reaction pathway," Kohler says.
"But now we have
a much-needed understanding of a key step in this process, and are developing
enzymes to fit our end goals of lowering the cost of biofuels by making
products from lignin."
