biostudies-literatureUnknown16Ude EOThe anammox bacteria "<i>Candidatus</i> Kuenenia stuttgartiensis" (<i>Ca.</i> Kuenenia) are able to gain energy by combining ammonium and nitrite to produce nitrogen gas, which is an ecologically and technically significant activity process. In this reaction, nitric oxide serves as a recognized intermediate in the reduction of nitrite, which is subsequently combined with ammonium to produce hydrazine. However, the enzyme that converts nitrite to nitric oxide remains elusive. In this study, we investigated the nitrite-reducing activity in "<i>Ca.</i> Kuenenia stuttgartiensis" strain CSTR1 to identify candidates for such an enzyme. An optimized <i>in vitro</i> assay was established to measure nitrite-reducing activities, with which we followed the activity in protein fractions obtained from Frontiers in microbiology1483703https://www.ebi.ac.uk/biostudies/studies/S-EPMC11897245biostudies-literatureFractionating proteins with nitrite-reducing activity in "<i>Candidatus</i> Kuenenia stuttgartiensis" strain CSTR1.PMC11897245Rimjhim RDing CAdrian LSure PUde EOfalseFractionating proteins with nitrite-reducing activity in "<i>Candidatus</i> Kuenenia stuttgartiensis" strain CSTR1.The anammox bacteria "<i>Candidatus</i> Kuenenia stuttgartiensis" (<i>Ca.</i> Kuenenia) are able to gain energy by combining ammonium and nitrite to produce nitrogen gas, which is an ecologically and technically significant activity process. In this reaction, nitric oxide serves as a recognized intermediate in the reduction of nitrite, which is subsequently combined with ammonium to produce hydrazine. However, the enzyme that converts nitrite to nitric oxide remains elusive. In this study, we investigated the nitrite-reducing activity in "<i>Ca.</i> Kuenenia stuttgartiensis" strain CSTR1 to identify candidates for such an enzyme. An optimized <i>in vitro</i> assay was established to measure nitrite-reducing activities, with which we followed the activity in protein fractions obtained from 2025-01-01T00:00:00Z20252026-04-08T19:50:12.331Z2025-04-04T01:28:47.778ZS-EPMC118972454007855410.3389/fmicb.2025.1483703