From fringe to electromicrobiological mainstream

Trained as a microbiologist, Ken Nealson pursues many interdisciplinary endeavors. He was a pioneer in the field of geomicrobiology and has worked on astrobiology and microbial fuel cells. He holds posts at the University of Southern California in Los Angeles and the J. Craig Venter Institute in San Diego, where he uses genomics to survey microbial diversity in the oceans. He recently spoke with Science News managing editor Eva Emerson.

KEN NEALSON Now, I think people are starting to realize this ability of bacteria to interact with the environment in an electrical way. Philip Channing/USC College

Tell me about “electromicrobiology.”

I think in 20 years, this may well be a major field. What we’re learning about is the ability of microbes to transfer electrons to different surfaces. When we first discovered this, it was really thought to be either a mistake or that the organism [we had discovered] was so far out-of-bounds from what other organisms do that the finding almost didn’t make any difference.

These were the Shewanella bacteria, which you showed could use metals as electron acceptors in respiration.

Yes, we discovered Shewanella about the same time Derek Lovley [of the University of Massachusetts Amherst] discovered Geobacter…. We found that these microbes were able to reduce solid substrates — iron oxide or manganese. Basically, you take a rock and take away all the oxygen and the bugs would just settle down and respire the rock…. I would say about 90 percent of the microbiological world thought this was some kind of artifact, that it wasn’t correct.

Now, 25 years later, everyone’s got a bug that does this. So now, I think people are starting to realize this ability of bacteria to interact with the environment in an electrical way. I mean, what are microbial fuel cells? These are just the same bacteria. Instead of giving their electrons to a rock, they give it to the anode of the fuel cell so we can harvest the electricity.

You take advantage of the electro-microbiology in the fuel cell. Are there other potential applications?

The one we really like to think about these days is could you use this to slow down or even totally inhibit corrosion? Corrosion is a many-billion dollar problem. And yet nobody really understands the role of bacteria in corrosion. And what is corrosion? It’s electron transfer from metals, it’s an energy-yielding reaction. So bacteria are smart: they sit there and they get the energy out of this. And by doing that, they speed it up. That’s my own hypothesis. And I’d say that many, many [corrosion] cases have to do with electromicrobiology — it’s the flow of electrons. So I wouldn’t be surprised if things like tooth decay or bone decay or dissolution of metals and minerals are all connected with this, specifically with what we call extracellular electron transport: the ability of these bugs to communicate electrically with the environment in ways that nobody taught us when we were students.

Scientifically, what’s most exciting?

It’s hard to separate the exciting science from all the applications … the exciting science are all these things that people didn’t believe 10 or 15 years ago — that a bacterium could actually have its enzymes on the outside of the cell and communicate with the environment electrically. To me that in itself is so exciting because it simply wasn’t in the textbooks 20 years ago and still is not there in most textbooks.

Where do you see electromicro-biology going next?

I think what you’ll see is that this ability is far more widespread than anyone thought and that biofilms will be intimately connected with this. Bugs sitting on surfaces, at the surface of the biofilm and 20 layers out, will be doing different things [physiologically] and that they’ll all be connected electrically one way or the other. And these electrons are going to flow even between microbial cells — like the things these guys are showing with nanowires [that link cells] (SN: 3/28/09, p. 16) — but these bugs don’t all need nanowires, because on the outside of the cells there are all of these enzymes. Sitting next to each other, the microbes can do it directly. And this is really an exciting concept: The world isn’t ready for it yet, but it’s getting close. 
I’ve now given four or five talks, and you can see that people are able to relate what you’re saying to something that they’ve seen….

This is sort of the progression of science. Where it goes from, “That’s impossible, this can’t be true,” over several steps, and the final step is, “Well, I knew it all the time.” … And so everybody and their brother is going to be studying this stuff, so you don’t need to do it anymore. And you look for something else, way out on the edge.

Unless I really miss my bet, I think in the next decade or so, this whole electro­microbiology thing will go from a fringe kind of science … to a major area of the field. So pretty soon, I’m going to have to find something new to do.