NF ix DB (Nitrogen Fixation DataBase)-a comprehensive integrated database for robust 'omics analysis of diazotrophs.

Biological nitrogen fixation is a fundamental biogeochemical process that transforms molecular nitrogen into biologically available nitrogen via diazotrophic microbes. Diazotrophs anaerobically fix nitrogen using the nitrogenase enzyme which is arranged in three different gene clusters: (i) molybdenum nitrogenase ( nifHDK ) is the most abundant, followed by it's alternatives, (ii) vanadium nitrogenase ( vnfHDK ) and (iii) iron nitrogenase ( anfHDK ). Multiple databases have been constructed as resources for diazotrophic 'omics analysis; however, an integrated database based on whole genome references does not exist. Here, we present NF ix DB (Nitrogen Fixation DataBase), a comprehensive integrated whole genome based database for diazotrophs, which includes all nitrogenases ( nifHDK , vnfHDK , anfHDK ) and nitrogenase-like enzymes (e.g. nflHD ) linked to ribosomal RNA operons (16S-5S-23S). NF ix DB was computed using Hidden Markov Models (HMMs) against the entire whole genome based Genome Taxonomy Database (GTDB R214), providing searchable reference HMMs for all nitrogenase and nitrogenase-like genes, complete ribosomal RNA operons, both GTDB and NCBI/RefSeq taxonomy, and an SQL database for querying matches. We compared NF ix DB to nifH databases from Buckley, Zehr, Mise and FunGene finding extensive evidence of nifH , in addition to vnfH and nflH . NF ix DB contains >4000 verified nifHDK sequences contained on 50 unique phyla of bacteria and archaea. NF ix DB provides the first comprehensive nitrogenase database available to researchers unlocking diazotrophic microbial potential.