Fixing carbon, unnaturally

A synthetic enzymatic pathway is more energy efficient than natural aerobic carbon fixation pathways Rising atmospheric carbon dioxide (CO 2 ) concentration as a result of extensive use of fossil fuel resources is one of the main causes of global warming. Natural photosynthesis converts 100 billion tons of CO 2 into biomass annually ( 1 ). Although natural photosynthesis plays a vital role in absorbing CO 2 emitted from fossil fuel use, it cannot prevent the net increase of atmospheric CO 2 concentration since the Industrial Revolution. Natural CO 2 fixation is mainly achieved by a CO 2 fixation pathway called the Calvin cycle, in which ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is the key enzyme. To date, six CO 2 fixation pathways, including the Calvin cycle, have been discovered ( 2 ). On page 900 of this issue, Schwander et al. ( 3 ) report a synthetic CO 2 fixation pathway that is more energy efficient than the Calvin cycle, expanding the capabilities for recapturing atmospheric CO 2 for use as a carbon feedstock.