Anammox bacteria require large amounts of iron for hydrazine synthase (HZS) and hydrazine oxidoreductase (HZO). By analyzing 8 anammox genomes across four genera, we found that only Candidatus Brocadia sinica harbors a compact genomic island (<10 kb) where hzs co-localizes with iron uptake ( TonB , FeoAB ) and Fe-S cluster assembly ( NifU / NifS ) genes. All other species show dispersed architectures (>100 kb separation). In the dispersed species Ca. Kuenenia stuttgartiensis , transcriptomic data revealed a 300- to 1500-fold excess of hzs over iron genes, indicating severe expression uncoupling. Thus, physical co-localization of iron support genes with anammox core enzymes is rare but exists in one Brocadia lineage, potentially enabling better co-regulation. These findings provide a genomic basis for predicting iron responsiveness across anammox species in engineered systems.
Significance Statement
Only Candidatus Brocadia sinica harbors a compact <10 kb iron-nitrogen genomic island.
All other anammox species show dispersed iron-nitrogen architectures (>100 kb separation).
Dispersed species exhibit 300⁓1500-fold expression mismatch between hzs and iron genes.
Physical co-localization may enable co-regulation of iron supply with anammox metabolism.
Genomic architecture predicts lineage-specific iron responsiveness in anammox engineering.