Quantitative metagenomics for marine prokaryotes and photosynthetic eukaryotes (radA and recA gene databases)

Most sequencing approaches yield only relative microbial abundances, limiting ecological and biogeochemical insights. Here, we present a spike-in quantitative metagenomics to estimate the absolute abundances of prokaryotes and eukaryotic phytoplankton in unfractionated seawater along the Atlantic Meridional Transect. By combining genomic internal standards with single-copy marker genes, this approach enables domain-spanning quantification with genus- to family-level resolution. We have uploaded FASTA files and DIAMOND blastx databases for the single-copy marker genes radA and recA. The recA database has been curated by removing sequences originating from human gut microbiota. To improve taxonomic coverage, we encourage researchers to expand this database with additional recA sequences, particularly from marine environments.