Identification of a B12 uptake protein in algae

Microalgae play an essential role in global net primary productivity and global biogeochemical cycling, but despite their phototrophic lifestyle over half of algal species are dependent on the corrinoid vitamin B12 (cobalamin) for growth. This essential organic micronutrient is produced by a subset of prokaryotic organisms only, which implies that in order for algal species to make use of this compound, they must first acquire it from external sources. Previous studies have identified protein components involved for vitamin B12 uptake in bacterial species and humans. However, little is known about how it is taken up in algae. Here, we use comparative genomics coupled with insertional mutagenesis and CRISPR-Cas9 knockouts and demonstrate the essential role of a protein, CBA1 (for cobalamin acquisition protein 1), in B12 uptake in Chlamydomonas reinhardtii and other algae.