The bacteria
Shewanella
oneidensis is a heavy metal fan. Its taste for
iron, lead and mercury make it useful for cleaning water
of these contaminants, and even better is the fact that
it generates electricity while it chows down. Now,
researchers at the University of California, Santa
Barbara (UCSB) have chemically modified the bacteria to
increase its energy production capabilities, which could
lead to
another way for wastewater treatment plants that
generate some of their own power.
Named after Oneida Lake, New York, where it
was first isolated in 1988,
Shewanella
oneidensis features proteins in its cell membrane
that conduct electrons and are essential for the cells'
respiration. To better harness the ability of the
bacterium's cells to produce energy as part of their
metabolism, the research team developed a synthetic
molecule called DSFO+, which modifies these cell
membranes but, since it contains iron, can still conduct
electrons.
Tested in two mutant strains of
Shewanella,
the team found that DSFO+ could not only completely
replace the natural current-conducting proteins, but do
their job more efficiently, boosting the power that the
microbe generated.
"The protein replacement molecule that we
constructed modifies the cell membrane so that it
facilitates respiration by electron delivery to the
membrane surface," says Guillermo Bazan, co-author of
the study. "It's a power-generating trick that gives us
an opportunity to look into the behavior of microbial
species in a way that didn't exist before."
Normally, scientists will make these kinds
of changes by genetically modifying an organism, but
it's a complicated process and, with all the red tape
designed to keep engineered microbes from "escaping"
into the wild, it's much harder to apply them to real
world situations. The juiced-up
Shewanella,
on the other hand, is chemically modified and its
effects are temporary: every time the bacteria
multiplies, the DSFO+ dilutes and eventually reverts to
its original state.
"We aided the metabolism of the bacteria,"
says Nathan Kirchhofer, co-lead author. "I think very
few people have approached this from a chemical
modification type of approach. We actually just took
bacteria as they were and added an external agent that
helps with their native process. To the best of our
knowledge, it is the first time this has been
demonstrated."
(From left) Nathan Kirchhofer, Zachary
Rengert and Guillermo Bazan, three of the researchers on
the project(Credit:
Sonia Fernandez)
In addition to being more efficient at
generating energy, the DSFO+ could also act as a kind of
power adapter between the electricity produced and the
manmade systems that could harvest it. In their natural
state, bacteria like
Shewanella
cannot electrically communicate with an electrode, but
this synthetic molecule could open up the possibility.
Eventually, the microbes could be used to not only break
down contaminants in wastewater, but in the process
generate enough electricity to recoup some of the cost
of that water treatment.
In the meantime, the researchers are hoping
to use the modified bacteria to study the internal
processes of the species, which could lead to further
breakthroughs and applications down the track.
"One idea is removing electrons, which is
common and easily performed," says Bazan. "But what
happens if we provide electrons to carry out chemical
reactions? Can we also monitor the health of that
microorganism by its electronic signatures? If we put a
drug in the organism, how does that impact its
metabolism? If we stress the microbe, how does it
breathe? If it's in a community of microorganisms, are
they sending electronic signatures to let each other
know what's going on? Can we intercept that? Can we
record that? These possibilities are becoming viable now
and open up fundamentally new avenues of research."
The study was published in the journal
Chem.