Weird Science

[kyonides]

I was reading this article that promised us all that there is another way to produce clean energy. My curiosity made me go straight to their source to verify it with my own  eyes.

Structural basis for bacterial energy extraction from atmospheric hydrogen

Diverse aerobic bacteria use atmospheric H2 as an energy source for growth and survival. This globally significant process regulates the composition of the atmosphere, enhances soil biodiversity and drives primary production in extreme environments.

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.

 What they are looking for is to produce energy out of a rare enzyme that does not suffer the effects of exposing itself to a high concentration of oxygen in the air. It would use hydrogen as its fuel and potentially, that would allow scientists to produce electricity.

How did they discover it?

Well, they first had to stop thinking they knew all about what was in charge of doing it.

The oxidation of atmospheric hydrogen (H2) by soils is a key biogeochemical process that shapes the redox state of the atmosphere. Until recently, this was thought to be an abiotic process, but it is now recognized that diverse aerobic bacteria from at least nine phyla oxidize atmospheric H2 and together account for 75% (around 60 Tg) of the total H2 removed from the atmosphere annually.

They believed the process would not involved any living creature, yet, a specific group of bacteria uses oxygen to capture free hydrogen molecules. What is quite interesting about it is the important part they play in such a process.

Why do they do it?

Atmospheric H2 oxidation provides bacteria with a supplemental energy source in nutrient-limited soil environments, enabling them to either grow mixotrophically or persist on air alone in a dormant but viable state for long periods...The ability to oxidize atmospheric H2 is widespread in bacteria from diverse environments, and some ecosystems—such as hyper-arid polar soils—appear to be driven primarily by atmospheric energy sources.

 What is mixotrophic anyway?
The dictionary tells us about it:

mixotrophic: deriving nourishment from both autotrophic and heterotrophic mechanisms —used especially of symbionts and partial parasites.

 OK, I guess we just got even more confused than we already were at the beginning. Let us dive a little bit more into the trophic world then.

autotrophic: requiring only carbon dioxide or carbonates as a source of carbon and a simple inorganic nitrogen compound for metabolic synthesis of organic molecules (such as glucose).

heterotrophic: requiring complex organic compounds of nitrogen and carbon (such as that obtained from plant or animal matter) for metabolic synthesis.

 This seems to tell us that such bacteria can get its nourishment from inorganic and organic components. They are basically looking for carbon dioxide and nitrogen plus some derivatives to stay alive and multiply themselves on their own.  But now we know that some of them survive thanks to consuming hydrogen as well! 

So what exactly takes care of the rest of the oxidation of hydrogen?

There are no known chemical catalysts that can oxidize atmospheric H2; this would require the selective oxidation of low concentrations of substrate (530 parts per billion by volume (ppbv)) present in an atmosphere containing a high concentration (21%) of the catalytic poison O2.

We need to recall that the  scientists were looking for the minuscule creatures that process hydrogen only. That lead them to these specific bacteria that could be exploited for energy production...

Recently, several high-affinity lineages of group 1 and 2 [NiFe] hydrogenases have been identified that input atmospheric H2-derived electrons into the aerobic respiratory chain. Whole-cell studies suggest that these enzymes have significantly higher apparent affinities for H2 (Km values 30 to 200 nM) and appear insensitive to inhibition by O2.

Before we even applaud and start jumping out of joy, we better keep reading  a little further to make sure we are not being controlled by our emotions.

However, given these hydrogenases have yet to be isolated, it remains unknown how they have evolved to selectively oxidize H2, tolerate exposure to O2 and interact with the electron transport chain. Notably, it is debated whether the hydrogenases responsible for the oxidation of atmospheric H2 have an inherently high affinity or whether their affinity is modulated by their interactions with the respiratory chain.

 Wait a second, guys! What are the hydrogenases they have mentioned above over and over again?

hydrogenase: an enzyme of various microorganisms that promotes the formation and utilization of gaseous hydrogen.

 This is confusing indeed. If we are talking about an alleged great discovery here, why does a dictionary like Merriam Webster register the term hydrogenase at all!?

What I mean is that finding out about their capabilities in recent months or years and publishing their discoveries on March 8, 2023 should take us all by surprise, wouldn't it?

Well, the answer might be that they got a method to prove that some bacteria do produce energy by consuming hydrogen BUT they cannot tell for sure which ones possess the heightened resistance to oxidation and partake in the production of energy.

 I guess this means that it could take them decades to come up with a method to separate them from the rest of the hydrogen eating bacteria and make them produce clean energy for us.

After all,  scientists began understanding the process and proving that those bacteria truly have an important role there just recently right?

So we have to conclude here that no, there is no new way to produce clean energy right away nor in the next few months for it is still being researched by several scientists.