Summary While mechanisms of different carbon dioxide (CO 2 ) assimilation pathways in chemolithoautotrohic prokaryotes are well understood for many isolates under laboratory conditions, the ecological significance of diverse CO 2 fixation strategies in the environment is mostly unexplored. Six stratified freshwater lakes were chosen to study the distribution and diversity of the Calvin‐Benson‐Bassham (CBB) cycle, the reductive...