Bacterial enzyme produces energy from atmospheric hydrogen

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"An enzyme that catalytically converts the hydrogen present in air into energy could find use in applications such as cheap and efficient hydrogen fuel cells. The enzyme, extracted from a bacterium ... is also insensitive to oxygen, unlike all other hydrogen-oxidizing catalysts, including platinum. ...
“This is in contrast to all known hydrogen-oxidizing catalysts that are not able to consume ambient levels of hydrogen.” ...
how Mycobacterium smegmatis is able to survive for years on end without having access to any organic food sources. This work led to a surprising discovery, recalls Greening: that the bacterium actually lives on air. “It takes up atmospheric hydrogen and uses this for aerobic respiration.” ...
Given that atmospheric hydrogen is a ubiquitous, diffusible and potent energy source, it provides a dependable lifeline for the survival of many bacteria, especially in nutrient-poor environments such as Antarctic soils, volcanic craters and the deep ocean. Until now, however, the researchers did not know how the bacteria exploit the trace amounts of hydrogen in the air. ...

In the new work, ... extracted Huc from M. smegmatis. By using advanced microscopy techniques like cryo-electron microscopy to determine its atomic structure and electric pathways, as well as employing electrochemistry, they showed that Huc turns minute concentrations of H2 gas into electrical current with extraordinary efficiency while being insensitive to oxygen (which usually acts as a “poison” for hydrogen-oxidizing catalysts). It does this by coupling oxidation of atmospheric H2 to the hydrogenation of the respiratory electron carrier menaquinone, using narrow hydrophobic gas channels to selectively bind the H2 at the expense of O2.

Huc is also robust to heat and can be heated to 80°C while retaining its ability to generate energy. ..."

From the abstract:

"... Atmospheric H2 oxidation is attributed to uncharacterized members of the [NiFe] hydrogenase superfamily. However, it remains unresolved how these enzymes overcome the extraordinary catalytic challenge of oxidizing picomolar levels of H2 amid ambient levels of the catalytic poison O2 and how the derived electrons are transferred to the respiratory chain. Here we determined the cryo-electron microscopy structure of the Mycobacterium smegmatis hydrogenase Huc and investigated its mechanism. Huc is a highly efficient oxygen-insensitive enzyme that couples oxidation of atmospheric H2 to the hydrogenation of the respiratory electron carrier menaquinone. Huc uses narrow hydrophobic gas channels to selectively bind atmospheric H2 at the expense of O2, and 3 [3Fe–4S] clusters modulate the properties of the enzyme so that atmospheric H2 oxidation is energetically feasible. The Huc catalytic subunits form an octameric 833 kDa complex around a membrane-associated stalk, which transports and reduces menaquinone 94 Å from the membrane. These findings provide a mechanistic basis for the biogeochemically and ecologically important process of atmospheric H2 oxidation, uncover a mode of energy coupling dependent on long-range quinone transport, and pave the way for the development of catalysts that oxidize H2 in ambient air."

Bacterial enzyme produces energy from atmospheric hydrogen – Physics World

Structural basis for bacterial energy extraction from atmospheric hydrogen (open access)

Extended Data Fig. 3: Cryo-EM visualisation and 3D reconstruction of the Huc oligomer.