Organisms can produce energy from air
The findings point to new possibilities for sustainable energy production
Researchers from the University of Bern, in collaboration with researchers from Australia and New Zealand, have recreated an important process in the laboratory that enables organisms to obtain Energy directly from components found in air. This confirms that certain organisms such as bacteria can actually live on air alone, without relying on sunlight or other energy sources. The findings point to new possibilities for sustainable energy production.
Hydrogen occurs in our atmosphere only as a trace gas, in a concentration of 0.00005%. The concentration remains almost constant, despite 70 million tons of newly produced hydrogen every year – mainly through photochemical processes and human-induced production. The reason for this constancy was unclear for a long time, but it is now known that most of it is absorbed by microorganisms such as bacteria in the soil, which use hydrogen as an energy source. Specialized enzymes, known as hydrogenases, capture the extremely rare hydrogen molecules from the air and convert them into energy.
Researchers from the University of Bern, together with colleagues from the University of Otago, Queensland University of Technology, Monash University and the University of Melbourne, have now succeeded for the first time in recreating the theoretical process of energy production by organisms from hydrogen in the air in the laboratory. The results, which have just been published in the scientific journal Proceedings of the National Academy of Sciences of the United States of America (PNAS), provide the first proof that the process actually takes place and explain, among other things, why certain organisms can survive for a long time without energy from the sun or other energy sources.
Hydrogen and oxygen react to form water and release energy
In chemistry lessons, this process of energy release is classically demonstrated using the oxyhydrogen reaction. Two parts hydrogen and one part oxygen are mixed in a balloon and ignited. The reaction produces a loud bang and the product of the reaction is water. The loud bang shows that the combination of these two gases is very energy-rich, but requires an initial energy in the form of heat. Christoph von Ballmoos, research group leader at the Department of Chemistry, Biochemistry and Pharmaceutical Sciences at the University of Bern and initiator and last author of the study, explains: "Basically the same reaction takes place in the bacterial cell. However, it is strictly catalyzed by enzymes and does not require an initial ignition. The reaction in bacteria is divided into at least three steps in order to store the released energy in the form of cellular energy ATP instead of losing it as heat, as in the oxyhydrogen experiment".
ATP (adenosine triphosphate) is the most important source of energy in the cell and is used for numerous tasks such as food intake or the production of DNA and proteins. ATP acts like a small rechargeable battery, which is regenerated after use.
To test whether this theoretical process can actually take place in organisms, the researchers reconstructed a minimal, synthetic respiratory chain from purified components. Von Ballmoos says: "In humans, cellular respiration takes place in the mitochondria and converts the energy from food into ATP. In the process, electrons are gradually transferred from energy-rich molecules to oxygen. The energy released in this way is used to drive a proton cycle, which generates ATP by means of a nanoturbine." In the current study, the researchers produced a minimal, synthetic respiratory chain from just three enzymes embedded in an artificial lipid membrane – one of which (the hydrogenase) came from Australia, the other two (proton pump and nanoturbine) from Bern. "One difficulty of this experiment that we were finally able to overcome was to incorporate the proteins into the membrane in such a way that the protons are pumped in the right direction," says Stefan Moning, second author of the study and doctoral student at the Department of Chemistry, Biochemistry and Pharmaceutical Sciences at the University of Bern.
Life from air is possible
The experiments support the theory that certain organisms can only produce the energy they need to live from the components of air. "Although hydrogen is only present in the air in vanishingly small quantities, the three enzymes manage to conserve the energy from the reaction and convert it into ATP. This is even more impressive given that oxygen is 400,000 times more abundant in the air than hydrogen, far from the ideal conditions of the oxyhydrogen reaction. Although the process is slow, it is sufficient to keep an organism afloat in bad times, as we have calculated," says von Ballmoos.
"This process not only explains why the hydrogen concentration in the atmosphere remains constant, but also why life is possible in the dry Antarctic desert despite the absence of organic molecules or why organisms can survive long periods without an energy source," says Sarah Soom, first author of the study and former Master's student at the Department of Chemistry, Biochemistry and Pharmaceutical Sciences at the University of Bern. "It is assumed that other trace gases in the air, such as carbon monoxide or methane, enable similar processes. But it has now been shown experimentally for the first time with hydrogen. The idea that you can actually live on air is fascinating," says von Ballmoos.
Reaction enables sustainable energy production
The reaction of hydrogen with oxygen has pure water as its only waste product. "This makes the method one of the most environmentally friendly forms of energy generation, comparable to that from sunlight," says Soom.
"The speed of ATP production can be increased many times over if the hydrogen is present in higher concentrations. If this can be achieved, for example through light-catalyzed water splitting, the process could set new standards for ATP production in synthetic biology," says von Ballmoos. The continuous and sustainable production of ATP is important, for example, for enzyme-supported drug production or understanding the origin of life in model systems. "There are still many unanswered questions and the synthetic respiratory chain can be further optimized. However, the work is a milestone towards feasibility and a start for further exciting potential applications," concludes von Ballmoos.
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