Algal carbon concentrating drives fatty acid biosynthesis beyond photosynthesis

The global carbon cycle underpins Earth’s sustainability, with algae playing a pivotal role in biological carbon assimilation. Efficient photosynthetic carbon fixation in aquatic environments is facilitated by algal CO2-concentrating mechanisms (CCMs). Despite their importance, the coordination of inorganic carbon demands for photosynthesis with other inorganic carbon-utilizing pathways remains unexplored. Here we use the model green alga Chlamydomonas reinhardtii to demonstrate that under limited-CO2 conditions, the biotin carboxyl-carrier protein subunit of acetyl-CoA carboxylase complex—the rate-limiting enzyme in de novo fatty acid biosynthesis—forms dynamic protein condensates at the pyrenoid periphery, partially co-localizing with the putative carbonic anhydrase LCIB. Furthermore, CCM-deficient mutants exhibit compromised fatty acid biosynthesis capacity. We propose a metabolic interaction between CCM and de novo fatty acid biosynthesis, which potentially optimizes cellular carbon economy, enhances biofuel production yields and, more broadly, reveals a molecular mechanism for coordinating inorganic carbon utilization within global carbon cycle.