Discovery of soil bacteria may allow us to produce electricity from ‘thin air’: ScienceAlert

It may sound surprising, but when times are hard and no other food is available, some soil bacteria can consume traces of hydrogen in the air as a source of energy.

In fact, bacteria remove a staggering 70 million tons of hydrogen from the atmosphere annually, a process that literally shapes the composition of the air we breathe.

We have isolated an enzyme that enables some bacteria to consume hydrogen and extract energy from it, and found that it can produce an electric current directly when exposed to even small amounts of hydrogen.

As we report in a new paper in Naturethe enzyme may have significant potential to power small, sustainable air-powered devices in the future.

Bacterial genes hold the secret to turning air into electricity

Prompted by this discovery, we analyzed the genetic code of a soil bacterium called Mycobacterium smegmatiswhich consumes hydrogen from the air.

Inscribed in these genes is the blueprint for producing the molecular machine responsible for consuming hydrogen and turning it into energy for the bacterium. This machine is an enzyme called a “hydrogenase,” and we called it Huc for short.

Hydrogen is the simplest molecule, made of two positively charged protons held together by a bond formed by two negatively charged electrons. Huc breaks this bond, the protons separate and the electrons are released.

In the bacteria, these free electrons then flow into a complex circuit called the “electron transport chain” and are used to supply the cell with energy.

Liquid electrons are what electricity is made of, meaning Huc directly converts hydrogen into electrical current.

Hydrogen represents only 0.00005 percent of the atmosphere. Ingesting this gas at these low concentrations is a formidable challenge that no known catalyst can achieve. Furthermore, oxygen, which is abundant in the atmosphere, poisons the activity of most hydrogen-consuming catalysts.

A map of the atomic structure of the Huc enzyme. (Rhys Grinter/CC BY-NC)

Isolation of the enzyme that allows bacteria to live on air

We wanted to know how Huc overcomes these challenges, so we set out to isolate it M. smegmatic cells.

The process to do this was complicated. We first modified the genes in M. smegmatic which enables the bacteria to make this enzyme. By doing this, we added a specific chemical sequence to Huc that allowed us to isolate it from M. smegmatic cells.

It wasn’t easy to get a good look at Huc. It took several years and quite a few experimental dead ends before we finally isolated a high-quality sample of the genius enzyme.

The hard work was worth it though, as the Huc we finally produced is very stable. It can withstand temperatures from 80 ℃ down to -80 ℃ without loss of activity.

The molecular blueprint for extracting hydrogen from air

With Huc isolated, we set about studying it in earnest to find out exactly what the enzyme is capable of. How can it turn the hydrogen in the air into a sustainable source of electricity?

Remarkably, we found that even when isolated from the bacteria, Huc can consume hydrogen at concentrations far lower than even the minute traces in the air. In fact, Huc was still consuming odors of hydrogen that were too faint to be detected by our gas chromatograph, a very sensitive instrument we use to measure gas concentrations.

We also found that Huc is completely uninhibited by oxygen, a property not seen in other hydrogen-consuming catalysts.

To assess its ability to convert hydrogen into electricity, we used a technique called electrochemistry. This showed that Huc can convert small concentrations of hydrogen in air directly into electricity, which can power an electrical circuit. This is a remarkable and unprecedented achievement for a hydrogen consuming catalyst.

We used several cutting-edge methods to study how Huc does this at the molecular level. These included advanced microscopy (cryogenic electron microscopy) and spectroscopy to determine its atomic structure and electrical pathways, pushing boundaries to produce the most resolved enzyme structure yet reported by this method.

Illustration of a complicated molecule running along a membrane surrounded by hydrogen molecules
Illustration of Huc consuming hydrogen from air. (Alina Kurokhtina)

Enzymes can use air to power tomorrow’s devices

It is early days for this research and several technical challenges must be overcome to realize the potential of Huc.

First, we will need to significantly increase the scale of Huc production. In the lab we produce Huc in milligram quantities, but we want to scale this up to grams and eventually kilograms.

But our work shows that Huc acts as a “natural battery” that produces a sustained electric current from air or added hydrogen.

As a result, Huc has significant potential in developing small, sustainable air-powered devices as an alternative to solar energy.

The amount of energy provided by hydrogen in the air would be small, but probably sufficient to power a biometric screen, watch, LED globe or simple computer. With more hydrogen, Huc produces more electricity and can potentially power larger devices.

Another application would be the development of Huc-based bioelectric sensors to detect hydrogen, which could be incredibly sensitive. Huc could be invaluable in detecting leaks in the infrastructure of our burgeoning hydrogen economy or in medical settings.

In short, this research shows how a fundamental discovery of how bacteria in soil feed themselves can lead to a new understanding of the chemistry of life. Ultimately, it can also lead to the development of technologies for the future.The conversation

Chris Greening, Professor, Microbiology, Monash University; Ashleigh Kropp, PhD Student, Biomedicine Discovery Institute, Monash University, and Rhys Grinter, Lab Head, Biomedicine Discovery Institute, Monash University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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