Iron-oxidizing bacteria could be used to convert electricity into biofuel
By David Szondy
January 31, 2013
What do bacteria, wind turbines and solar panels have to do with one another? Nothing ... unless you can teach the bacteria to “breathe” electricity and turn it into biofuel. That’s still a very long way off, but a team of researchers at the BioTechnology Institute at the University of Minnesota - Twin Cities have found a method for growing iron-oxidizing bacteria by feeding it electricity. It’s primarily a way to better study a recently-discovered type of bacteria, but it also holds the promise of turning electricity into biofuel.
The bacteria in question is Mariprofundus ferrooxydans PV-1. It’s an aerobic bacteria that was first found in deep ocean volcanic vents, but has since been discovered in estuarine and marine habitats all over the world. According to the team, the fact that it prefers to live at the interface where an aerobic environment meets an anaerobic one makes it difficult to study, because of the many problems involved in its cultivation.
Mariprofundus is one of a group of bacteria responsible for what is known as “biocorrosion.” We tend to think of rusting iron as being a simple chemical process, but a surprising amount is caused by bacteria. If you look at images of the wreck of the RMS Titanic, you’ll see what looks like brownish-red melted wax streaming down the hull. These structures are “rusticles” and they are formed by a bacteria similar to Mariprofundus. The process also occurs in places much closer to home, with bacteria happily munching away in caves and on steel pipelines, bridges, piers, and ships.
The interesting thing about Mariprofundus is that it “breathes” electrons. Normally, to grow and reproduce, it lifts electrons off of a form of dissolved iron called Fe (II), also known as iron (II) oxide. This turns it into a solid precipitate of Fe(III) (iron (III) oxide). Another word for this precipitate is “rust.” This makes the bacteria very interesting to scientists, but also very hard to cultivate.
The University of Minnesota team’s breakthrough was in developing what they call “electrochemical cultivation.” This involves supplying the bacteria with a stream of electrons so it can “breathe.”
“It’s a new way to cultivate a microorganism that’s been very difficult to study. But the fact that these organisms can synthesize everything they need using only electricity makes us very interested in their abilities,” said Daniel Bond, who co-authored a paper on the project with Zarath Summers and Jeffrey Gralnick.
It’s believed that the bacteria’s electron-swapping breathing takes place on the microbe’s surface. If that’s the case, the team reasoned, electrons could be applied directly to it instead of through iron. They placed the Mariprofundus in a nutrient solution that contained no iron. Instead, an electrode was introduced and an electric current applied. It wasn’t long before the bacteria multiplied and the electrode was coated with a film of them. In other words, the bacteria were feeding off electricity that they combined with carbon dioxide to grow and reproduce.
For the scientists, this makes it much easier to study the bacteria, because they can now cultivate it without problems such as eliminating concentration issues, side reactions, and mineral end products.
For the general public, the greater significance is the promise it holds. If the process could be scaled up and controlled, it could be used in the future as a way of storing electricity generated by wind or solar power by using the bacteria to make biofuel. However, as is often the case with microbiology, there are still many more steps before a practical process can be developed to maintain even small production levels.
The team’s results were published in the journal mBio.