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."
