Summary Ribulose 1,5‐bisphosphate carboxylase/oxygenase ( RubisCO ) is a critical yet severely inefficient enzyme that catalyses the fixation of virtually all of the carbon found on E arth. Here, we report a functional metagenomic selection that recovers physiologically active RubisCO molecules directly from uncultivated and largely unknown members of natural microbial communities. Selection is based on CO 2 ‐dependent growth...