ATP synthesis driven by atmospheric hydrogen concentrations

Abstract

All cells require a continuous supply of the universal energy currency, adenosine triphosphate (ATP), to drive countless cellular reactions. The universally conserved F₁F_o-ATP synthase regenerates ATP from ADP and P_i by harnessing a transmembrane electrochemical proton gradient (<i>pmf</i>). Bacteria have evolved diverse <i>pmf</i>-forming strategies using light, organic, and inorganic energy sources. Recently, we proposed that many bacteria survive using atmospheric trace gases to produce ATP when limited for other energy sources. However, direct evidence that atmospheric energy sources are sufficient to generate <i>pmf</i> or drive ATP synthesis is still lacking. Here, we show that the membrane-associated hydrogen:quinone oxidoreductase Huc from <i>Mycobacterium smegmatis</i> can enable ATP synthesis from air. Purified Huc couples H₂ oxidation to the reduction of various ubiquinone and menaquinone analogues. We designed a minimal respiratory chain in which Huc interacts with liposomes containing the nonpumping, but <i>pmf</i>-generating, <i>bd</i>-I oxidase and F₁F_o-ATP synthase from <i>Escherichia coli</i>. Our experiments show that passive hydrogen exchange from air to solution is sufficient for the electron transfer and <i>pmf</i> generation required to accumulate ATP. By combining continuous culture bioenergetics measurements with theoretical calculations, we show this process is sufficient for mycobacteria to sustain <i>pmf</i> and ATP synthesis (two ATP molecules per H₂ oxidized) for maintenance energy requirements during nutrient starvation. These findings confirm that atmospheric energy sources can be dependable 'lifeline' substrates that enable continuous energy conservation during nutrient starvation. In addition, this work provides a unique tool for ATP production in synthetic applications, which unlike other approaches is traceless without by-product accumulation.