De novo synthesis of fatty acids in Archaea via an archaeal fatty acid synthase complex

Archaea synthesize membranes using isoprenoid-based ether lipids, whereas Bacteria and Eukarya use fatty acid-based ester lipids. While the factors responsible for this "lipid divide" remain unclear, this has important implications for understanding the evolutionary history of eukaryotes, which likely originated from within the Archaea and therefore changed membrane composition from isoprenoid-based to fatty acid-based lipids. Here, using 13C labelling studies, we demonstrate that the archaeal model organisms Sulfolobus acidocaldarius and Haloferax volcanii are capable of de novo fatty acid synthesis. Biochemical characterization and in vitro pathway reconstitution identify the key enzymes of a newly proposed fatty acid synthesis pathway in S. acidocaldarius and show that ketothiolase, ketoacyl-CoA reductase, and hydroxyacyl-CoA dehydratase form a stable assembly mediated by a DUF35 domain protein, which represents the first characterization of an archaeal fatty acid synthase complex. The final step is catalysed by an NADPH-dependent enoyl-CoA reductase. Deletion of the enoyl-CoA reductase demonstrate that this pathway operates in vivo in S. acidocaldarius. The presented results including phylogenetic analysis reveal that the potential to synthesize fatty acids is widespread across archaeal lineages. Collectively, our findings demonstrate that archaea are capable of synthesizing fatty acids, elucidate the molecular mechanisms involved in this process and provide additional insights into the evolutionary histories of fatty acid synthesis in archaea.