Abstract
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.