The atmosphere provides most of the oxygen, carbon, and nitrogen that we depend on, but until now has been thought to lack sufficient energy to sustain life. Here I will demonstrate that diverse microbes live by harvesting the small amounts of hydrogen and carbon monoxide from air using high-affinity enzymes. Through research focused on the model bacterium Mycobacterium smegmatis, I will explain the physiological role, genetic regulation, and structural basis of this process. This depends on hydrogenases and carbon monoxide dehydrogenases with structural features that confer high affinity and oxygen insensitivity. These enzymes rely on the newly discovered but widely distributed process of long-range quinone transport to transfer electrons to the respiratory chain. Culture-based and culture-independent evidence will be presented that microorganisms from multiple phyla and diverse environments also meet their energy needs through this process. Finally, I will reveal that certain ecosystems are primarily powered by atmospheric energy sources, and show the enzymes involved can be harnessed in biotechnology to produce electricity and ATP from air. These findings redefine the minimal requirements for life and have broad climate, medical, and astrobiological implications.​

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