In my last post, I wrote about how eating and breathing are equally necessary to power your body. In the bodies of animals (like yours) having sugars meet oxygen in the cells produces quick electrical currents that create the energy animals need to survive.
All living things need to eat (or produce) food and to breathe oxygen to get the energy they need, except for some microbes. There are a bunch of microbe species that don’t need oxygen (and some microbes that don’t really need food; they basically eat electricity).
These microbes that make electricity without oxygen can power a battery. I know this because I have a microbe-powered battery in my house right now. It looks like this:
This is called a MudWatt battery. See that brown stuff in it? That is literally mud. The mud itself does not produce electricity. The microbes inside of it do. They can produce enough electricity to run a clock.
You may think in order for this battery to produce electricity, the MudWatt battery has to come with special microbe-filled mud, but…
…mud is not included in this battery. You have to provide the mud and the microbes yourself.
Luckily, you can find the right kind of microbes pretty much anywhere you choose to stick in a shovel. To build our battery, my lab partner and I decided to get the muddiest mud we could find by going to a pond not too far from my house.
Then we hooked up the wires that would collect the electricity from the microbes.
Once you set-up the battery, the bulb does not light up right away, so don’t expect instant gratification. Because microbes are microscopic, a lot of them need to be living in the battery to produce enough electricity. By "a lot," I don't mean, like, 40. My battery currently has 291,666,673.185925 bacteria living inside of it (though I'm not sure what 0.185925 of a bacterium looks like).
So it will take a few days for the bacteria to reproduce until there are enough of them to get the light bulb flashing (It took a couple weeks for them to light up the bulb in my battery, and when that happened, I became much more excited than you might expect a 44-year old man to be).
So how do these microbes do this?
The microbes producing electricity in the battery (and in soils pretty much everywhere) are different species of Shewanella and Geobacter bacteria. If you were able to look at these types of bacteria with a high-powered microscope, they would look like this:
These bacteria usually live underground in places that do not have oxygen. Without oxygen, they need to breathe something else to turn their food into usable energy. For many Shewanella and Geobacter bacteria, the “something else” they breathe is metals, like iron.
Yes, Virginia, some bacteria breathe metal. That does not mean you can put a car in front of a Shewanella bacteria and then watch the car get breathed up the Shewanella’s nose. For one thing, bacteria don’t have noses. For another thing, “breathe” is not the best word I could have used. We breathe oxygen because we need oxygen in our bodies for our cells to do respiration (respiration is the process I described in my last post where chemical reactions occur within cells to break down food and make the kind of energy the cells need). Shewanella and Geobacter do respiration outside their bodies, so they do not need to breathe anything in their bodies. Instead, they need to get in contact with something outside their body that is good at attracting electrons.
Shewanella and Geobacter bacteria use metal for respiration because, like oxygen, metals are electron magnets. These bacteria look for metal in the soil and rock where they live. When Shewanella and Geobacter bacteria find metal, they can connect to it for respiration in three ways.
- Grow right on the metal
- Grow filaments (long, living, string things) until they reach and attach to the metal. The filaments then act like living electrical wires. Scientists call them "nanowires.". (You can watch videos of bacteria growing nanowires here. You can also see nanowires on the photo of the Geobacter bacteria above.
- Make some riboflavin. Riboflavin can pick up loose electrons from inside the bacteria and carry them to the metal like an electron shuttle bus. (You are (hopefully) eating riboflavin regularly, because riboflavin is also called Vitamin B2).
Each of these methods allow the metal to suck up the bacteria’s electrons like an electron vacuum cleaner and turn the bacteria's food into usable energy.
The MudWatt battery provide metal to the bacteria. When you set-up the battery, you put a wire with a disc attached to it in the mud. This part of the wire is called an anode. The anode puts a relatively large amount of metal in the mud that a multitude of microbes can then use for respiration. All that extra metal allows more bacteria to live there, so the bacteria keep reproducing and their population keeps growing until they are producing lots of electricity
The population would not be able to grow, though, if there is not enough food for them to eat (remember, respiration turns food into usable energy). These Shewanella and Geobacter bacteria get their food by eating sugars in the soil. All living things have sugars in them (as well some nonliving things, like Twinkies). Soils are full of decomposed bits of living things, including sugars. One of the reasons I got mud from the edge of a wetland pond for my battery is the soil in wetlands tends to be rich in organic materials, including lots of sugars. If I had used dirt from my backyard, which would not have as much organic stuff as the marsh mud, I would have added ketchup to the soil. That is actually what the MudWatt people recommend you do. You do not add ketchup to make the mud taste good to finicky bacteria, but because most store-bought ketchup is basically tomato-flavored sugar juice.
The ketchup adds sugar to the mud that the bacteria can then eat.
As the anode attracts electrons, it creates an electron party inside the anode that every electron wants to get out of because electrons have no interest in hanging out with each other. The wire from the mud to the circuit and the light bulb provides an escape route for all these anti-social electrons. As they travel away from each other through the wire, the electrons provide the electrical energy the light bulb needs.
Scientists are unsure whether these microbes will ever be able to produce electricity in a way that we can cheaply and directly use to power our homes, but the microbes have the potential to help us in a lot of other ways. Scientists feel confident that these microbes may be able to help us make powerful hydrogen fuel cells. We also may be able to use the nanowires in electronics as highly conductive, microscopic wires that do need to be manufactured in ways that produce pollution. And, since some of the bacteria can breakdown a variety of metals, they may be able to help clean-up pollution around the world. The discovery of these amazing microbes will benefit us in many ways beyond just lighting a bulb in my basement.
To learn more about metal-breathing, electricity-producing microbes, read my free eBook Where Wild Microbes Grow.
You can learn more about the MudWatt Battery and even buy your own kit at the MuddWatt website.
PS. Thank you to Keegan Cooke and Kevin Rand, the inventors of the MudWatt Battery, for providing me with two free MudWatt battery kits to play with. Also thanks to Ann Estes, who created the wonderful website Mostly Microbes, for introducing me to Keegan and Kevin.
Online references and resources
Mental_floss. "Create a Battery from Mud."
MicrobeWiki. "Shewanella oneidensis MR-1: Background and Applications."
PBS Newshour. "Suffocating cells for science."
PHYS.org. "Bacterial nanowires: Not what we thought they were."
PRI. "'Bacterial nanowires' may lead to breakthroughs in semiconductors, fuel cells and more."
Photos and Images
All the photos and the GIF were taken by me, except the two microscopic images of bacteria. Click those images to find their sources.