How do you introduce yourself, scientifically? 

My name is Brandon Enalls and I am a geomicrobiologist. I’m interested in how energy moves between geological and biological processes in several different environments on Earth. More specifically I’m interested in microbes, which are microscopic organisms like bacteria, living at deep sea hydrothermal vents (Figure 1). 

Figure 1: A deep sea hydrothermal vent. Source: Dr. Bob Embley. Licensed under CC BY 2.0

I study microbes that can conduct electricity, taking electrons from minerals like pyrite (Figure 2) in order to power their biological processes.  

Figure 2: Pyrite. Source: “Pyrite” by Didier Descouens. Licensed under CC BY-SA 4.0

What are the implications or broader impacts of your work? 

Many organisms, including humans, generate the molecule ATP, which provides energy for our cells,  partially through a series of ‘electron transfer reactions’ that occur near our cell membranes. But humans have to bring molecules from our food into the cells themselves to be able to power these electron transfer reactions. The microbes I study can use electrons from materials outside the cell to power these reactions; they engage with the environment without actually having to bring anything into their cells. 

I work at hydrothermal vents mostly because they are naturally electrically conductive environments, and there may be many electroactive microbes that live there. But we don’t know how widespread these electroactive microbes are in other environments, or to what extent they are actually using this process of taking electrons from minerals to help power their metabolisms. There is some basic interest in these processes from a biological standpoint. 

There are also some geological implications for this work – the physical and chemical properties of minerals can change as electrons are pulled away from them. So not only can these microbes take advantage of these naturally occurring electrical currents in their environment, but they can also change the geology of their environment. 

Can you explain some of the steps that go into collecting your data? 

Our lab and collaborators regularly go out in the field to collect samples of microbes. In our case this means using a research vessel to go to the middle of the Pacific Ocean where these hydrothermal vents exist, usually along tectonic plate boundaries. We use either a remote operated vehicle or a human occupied submersible to go 1,000 or more meters below sea level and collect samples. I’ve personally gone out to sea once for fieldwork, but I can do most of my work in the lab on land so I often ask collaborators to send back samples for me. Each sample fits in a mason jar.

When we get back to the lab, I can take these samples and set them up with electrodes (Figure 3) to start taking measurements. It usually takes a few weeks to get measurements from a single sample.

Figure 3: Photo of an electrode. Source: Brandon Enalls.

What does your data look like? 

Most of my experiments are conducted using what we call bioelectrochemical systems. My samples of microbes are exposed to electrodes (2.5×2.5 centimeter squares that carry electrical current) that we can set to carry a specific electrical current mimicking minerals that occur at hydrothermal vents (Figure 3). The idea is that the microbes might be able to use the electrons on the electrode instead of the electrons they would normally get from minerals. The main data point I take from this is electrical current measurements over time. I can quantify the number of electrons being transferred to the microbes, which helps me understand how active these microbes are. 

When I’ve finished these measurements, I will often extract DNA from the surfaces of the electrodes in order to figure out exactly which microbes we were working with to get our electrical measurements. There is one particular gene that we look at to determine where these microbes fit into the tree of life.

What happens after you collect your data? 

I convert the raw electrical current measurements into numbers that are more tangible, and then I can plot the electrical current over time to see how electrically active the microbes were during the experiment. For my DNA extraction data, I’ll mostly look to see what specific microbes were present in the sample when I started and ended a particular experiment. 

Using these pieces of information, we can make some guesses as to which microbes were electrically active based on which ones increased in abundance over time. If the relative abundance of one or more microbes increases over the course of the experiment, we can say that these specific microbes may be electrically active. 

Figure 4: Brandon in the lab. Source: Brandon Enalls.

What makes a geomicrobiologist different from other scientists? 

I think the best thing about geomicrobiology is that it’s truly an interdisciplinary field. You need to have an understanding of both biology and geology. That knowledge helps us understand the context for the processes that we are interested in studying. I think I’m a microbiologist at heart, but most of the microbes that I work with now haven’t yet been cultivated in the lab. So, I can’t use more traditional microbiological techniques (genetic tools, growing populations of single species in culture, etc.). But instead, we use electrochemistry as a powerful tool to circumvent the need for those tools and study these systems where geology and microbes interact. 

Is there a common misconception about your field? 

Microbes are very small, so I think they can seem abstract, and it can be difficult to imagine that what they do matters. But they are actually major players in shaping how our world has changed over geological time. A good example of this is cyanobacteria. Cyanobacteria photosynthesize and generate oxygen as a waste product. This is the reason why we have oxygen in our atmosphere right now – cyanobacteria were able to photosynthesize over two billion years ago, and this led to the introduction of oxygen into the atmosphere and the planet becoming habitable for humans and other animals and plants today. Microbes are small but they have a huge impact.

Is there anything you would tell people interested in becoming a geomicrobiologist?

The coolest thing about geomicrobiology is that you can work on systems pretty much anywhere on the earth. Microbes are ubiquitous, and they mediate so many interesting processes that it would be hard not to find something interesting to study even in your backyard. As a geomicrobiologist you can study what chemical and physical features of an environment are able to influence the types of microbes found in that environment. But you can also study the reverse– how microbes themselves influence the physical and chemical content of the environment. If you can think about science in that kind of framework, you are already on track to being a geomicrobiologist. 


To learn more about Brandon’s work: 

  • Follow him on Twitter:@BrandonEnalls
  • Check out some videos about Brandon and his work: Video 1 and Video 2

This interview with Brandon Enalls, Graduate Student in the Department of Organismic and Evolutionary Biology at Harvard University, was conducted and edited for space and clarity by Malinda J. McPherson in August 2020. 

Malinda J. McPherson is a PhD candidate in the Harvard University/MIT Program in Speech and Hearing Bioscience and Technology.

Cover image: “expl1497” from Submarine Ring of Fire 2006 Exploration, NOAA Vents Program is licensed under CC BY 2.0.

This piece is part of our special edition on the day-to-day lives of researchers working in many different fields of science. Are you interested in learning about a different type of scientist? Check out the rest of the special edition!

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