Nitrotoxin metabolism in bacteria may have emerged from a diverse oxidoreductase reservoir

Bacterial transformation of 3 nitropropionic acid (3NPA) is typically viewed through canonical nitronate monooxygenases (NMOs), yet sequence annotation poorly resolves function across this flavoprotein family. Here we show that the environmental YrpB/NMO associated oxidoreductase space is dominated by YrpB related proteins: across 13 metagenomes, 83.1% of 390 conserved domain supported candidates were YrpB-associated. Cultivation along an Eisenia fetida feed gut cast continuum recovered 31 phylogenetically diverse 3NPA responsive bacteria, revealing that this phenotype is distributed across multiple lineages. Using the previously genome-sequenced Serratia sp. EWG9 as a tractable exemplar, we demonstrate sustained 3NPA supported growth, 44% parent compound depletion and a broad early transcriptional reorganization. Its focal oxidoreductase OXR01 occupies overlapping YrpB/NMO sequence space and shows stable predicted 3NPA accommodation without strong transcriptional induction. These findings reposition canonical NMOs as one component of a broader, ecologically distributed oxidoreductase reservoir for bacterial nitrotoxin responsiveness.