A recent article published in Nature magazine by Dr. Rhys Grinter, Ashleigh Kropp, a Ph.D. student, and Professor Chris Greening from the Monash University Biomedicine Discovery Institute in Melbourne, Australia indicates that the authors have discovered an enzyme that uses small amounts of hydrogen in the air to generate an electrical current. The enzyme, named Huc, was extracted from a bacterium called Mycobacterium smegmatis by the researchers. Dr. Grinter notes that this breakthrough discovery makes bacteria-powered devices or even powering a car possible in the future.

What is exciting about this finding is that the Huc enzyme can turn hydrogen into electricity at low atmospheric concentrations – as little as 0.00005% of the air we breathe, according to Dr. Grinter. Furthermore, it can function when there is oxygen, contrary to other types of enzymes which can not function when there is oxygen around. Mycobacterium smegmatis is easy to grow in the lab so it makes harnessing steady electricity by Huc enzymes achievable.

In the following interview, Dr. Grinter not only explains his research in detail but also outlines the future application of this discovery including in a harsh environment such as Mars.

Q: Your recent article published in Nature magazine about a discovery of an enzyme that converts air into electricity is very exciting. First of all, please share with us your educational and training backgrounds.
A: I received my junior and high-school education from a small school on Kangaroo Island in South Australia before receiving a bachelor’s degree in Biotechnology in 2005 from Flinders University in Adelaide, South Australia. After a few years break from studying, I conducted a Ph.D. in Microbiology and Structural Biology from the University of Glasgow in the UK. In 2015, after completing my Ph.D., I moved to Monash University in Melbourne, Australia, where I worked as a postdoctoral researcher investigating bacteria on a molecular level. In 2021, I founded my research group.

Q: Please tell us more about this amazing discovery that was published in Nature.
A: We isolated an enzyme called Huc from the soil bacterium Mycobacterium smegmatis, which converts the hydrogen in the air into electricity. The bacterium uses this enzyme to convert the hydrogen in the air into energy, especially when there are limited other sources of food. We showed that this enzyme could turn hydrogen into electricity at atmospheric concentrations (0.00005%), and if we give it more hydrogen, it produces more energy. We also showed that Huc works just as well when oxygen is present, which is exciting because many other molecules that convert hydrogen into electricity don’t work with oxygen present. We also used advanced (cryo-electron) microscopy to take a 3D picture of Huc at an atomic level. This told us a lot about how Huc can convert atmospheric hydrogen into electricity.

Q: Please tell us more about the molecular blueprint of atmospheric hydrogen oxidation that you developed. What else could you derive from this blueprint?
A: As mentioned above, we used advanced microscopy to see what Huc looks like on the atomic scale. This gave us many clues about how it can turn hydrogen in the air into electricity. While there is still more work to do to fully understand how Huc works, we can use this information to make it perform better or use this blueprint to design other enzymes or catalysts that can use hydrogen from the air.

Q: Other than Mycobacterium smegmatis, can Huc enzyme be extracted from other bacteria? Can Huc be synthesized?
A: Many soil bacteria produce enzymes like Huc. It’s estimated that between 60 and 80% of soil bacteria can use hydrogen from the air as an energy source using these enzymes. This is the major reason why the concentration of hydrogen in the air is quite low. However, to make a lot of Huc, you need to grow a lot of the bacteria that make it. This often isn’t easy to do for soil bacteria. We worked with Mycobacterium smegmatis for this work because it’s easy to grow a lot of it using a simple yeast-based broth.

Q: How is Huc different from other enzymes and what accounts for the difference?
A: Many other enzymes have been studied that can convert hydrogen into electricity. However, these enzymes are very different from Huc. Most of these enzymes can’t function when there is oxygen around, which considering oxygen forms 21% of the air, means they don’t work in the air. Importantly, no other enzyme that has been isolated can use hydrogen at low concentrations like that found in the air. This makes isolating Huc a major discovery, as we can now think about ways to use it to produce electricity.

Q: What kind of environment do these bacteria (M) live in; are they easily cultivated in the lab?
A: Usually, these bacteria live in the soil, although the Mycobacterium smegmatis was originally isolated from a rather delicate region of the human body. It’s quite an adaptable bacterium, so it tends to appear in many places. It is easily cultivated in the lab. You can feed it a variety of nutrients. However, we usually grow it in a liquid broth containing a mixture of yeast extract (a byproduct of beer brewing) and table salt (sodium chloride). It can be grown in small volumes (100ml to 10 liters) in flasks or larger volumes in a vat fermenter (15-100,000+ liters).

Q: Do the bacteria you use to produce any waste products?
A: Once M. smegmatis has been grown, it is separated from its growing liquid, which becomes a waste product of the process. This waste liquid isn’t toxic and can be dealt with using standard water treatment procedures, or the remaining nutrients can be recovered for future use.

Q: What sorts of bacteria-powered devices (e.g., batteries) do you envision? Can electricity be harnessed from these bacteria on a large scale?
A: Because the concentration of hydrogen in the air is quite low, Huc would only be able to power devices that require a small amount of power. However, there is the advantage that his power would be constant. We envisage that this might include a biometric monitor, an environmental sensor, a clock, or a small computer. However, we have shown that if you give Huc more hydrogen, then it will make more electricity. This gives Huc the potential to power larger devices if incorporated into a hydrogen-fed fuel cell. Possibly, larger devices with, including more complex computers (e.g. a smartphone or smartwatch), or maybe even a car.

Q: In an environment such as Mars without any oxygen, can this method still be applied?
A: This is a great question, to create electricity from hydrogen, you need a complete electrical circuit, meaning that the electrons produced need to go somewhere. On earth, the most convenient chemical to send the electrons to is oxygen, a job that can be performed by another well-studied enzyme, leading to water as a product. From a quick google search, there doesn’t seem to be much hydrogen on Mars. However, there is a lot of hydrogen in space. If we can find another molecule to give the electrons from hydrogen to, the Huc could be used to produce energy there.

Q: Besides this research, what other research areas interest you?
A: My general research interest is understanding how life, specifically bacteria, works on a molecular level. In addition to Huc, I am researching several other enzymes that convert gases in the air into electricity, including an enzyme that does this with Carbon Monoxide. My lab is also researching how disease-causing bacteria steal the essential nutrient iron from our bodies when they infect us. The idea here is that we may be able to block this process to stop bacterial infection. My lab is also working on discovering new protein-based antibiotics as next-generation treatments for antibiotic-resistant bacteria.