Scientists discover enzyme that can turn air into energy, unlocking potential new energy source

It has long been known that a relative of the tuberculosis bacteria can produce energy from the air's hydrogen. Scientists have now figured out how.

Researchers looking at a relative of the bacterium that causes leprosy and tuberculosis have found an enzyme that turns hydrogen into electricity, and they believe it could be used to produce a new, clean source of energy practically out of empty air.

The bacteria Mycobacterium smegmatis uses the Huc enzyme to extract energy from atmospheric hydrogen, allowing it to live in harsh, nutrient-poor habitats.

Now, the scientists claim they have discovered a new energy source that could be used to fuel a variety of tiny portable electronic devices by extracting and analyzing the enzyme. They released their results in the magazine Nature on March 8th .

"We imagine that a Huc-containing power source could power a range of small portable devices using air, including biometric sensors, environmental monitors, digital clocks, and calculators or simple computers," lead author Rhys Grinter, a microbiologist at Monash University in Australia, told Live Science via email.

Huc generates more electrical current when you give it more pure hydrogen, he explained. This implies that it could be used in fuel cells to power more sophisticated gadgets, such as smart watches, cellphones, more portable complicated computers, and potentially even a vehicle.

M. smegmatis is a nonpathogenic, quick-growing bacteria that is frequently used in laboratories to research the cell wall composition of Mycobacterium TB, a close relative that causes illness. In order to live in the harshest habitats, such as Antarctic soils, volcanic craters, and the deep ocean, where little other fuel can be found, M. smegmatis, a common soil bacterium found worldwide, has long been known to transform trace hydrogen in the air into energy.

But up until this point, it was unclear how M. smegmatis accomplished this.

The researchers used chromatography, a laboratory method that allows researchers to separate the components of a mixture, to first extract the Huc enzyme responsible for the process in order to study the chemistry underlying M. smegmatis' astonishing ability. They next used cryo-electron imaging, a method that earned its developers the 2017 Nobel Prize in chemistry, to examine the crystal structure of the enzyme. The researchers mapped the atomic structure of the enzyme and the electrical paths it uses to transport the electrons so that they create a current by beaming electrons onto a frozen sample of Huc that was collected from M. smegmatis.

The researchers found that Huc has an active site, a structure at its core that houses charged nickel and iron particles. The two protons and two electrons that make up hydrogen molecules are confined between the nickel and iron ions once they penetrate the active site and lose their electrons as a result. In order to create a current, the enzyme then moves these electrons along in a stream.

According to Grinter, the electrons are taken up by Huc (more precisely, the nickel ion) and transmitted to its surface by a molecular wire made of iron and sulfur ion clusters. "If we bind Huc on an electrode, the electrons can flow from the enzyme surface into an electrical circuit and produce electricity."

More research showed that the isolated Huc enzyme can be kept for a long time, that it can withstand being frozen or heated to 176 °F (80 °C), and that it can devour hydrogen at amounts as minute as 0.00005% of what is present in our air. These characteristics could make the enzyme a prime choice for a power source in organic batteries, the researchers say, along with the microbe's prevalence and ease of growth.

The amount of hydrogen in the air that Huc can take as electricity is practically infinite, according to Grinter. "Due to the low levels of hydrogen in the air, only a small quantity of energy can be produced. Huc can only be used in this situation for devices that need a tiny quantity of power over an extended period of time. Huc could also be used in fuel cells, which provide hydrogen in greater abundance."