Harnessing electricity-generating bacteria to clean up drinking water
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."
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.