anammoxosome

GO:0044222 · Membrane organelle · Membrane bounded organelle · Proposed

A ladderane-lipid-bounded intracytoplasmic organelle of anaerobic ammonium-oxidizing Planctomycetota that localizes the hydrazine-producing anammox catabolic pathway and its energy-conserving membrane reactions. [GO:0044222]

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Essential	Role
ladderane lipid membrane	Lipid	part of			ESSENTIAL	Dense lipid membrane that bounds the anammoxosome and separates toxic hydrazine-pathway intermediates from the cytoplasm. `DOI:10.1111/1574-6976.12014` Kartal et al. 2013 review ladderane lipids as the distinctive membrane lipids of the anammoxosome. `PMID:15098544` Sinninghe Damste et al. 2002 identified ladderane lipids as membrane lipids specific to anammox bacteria.
hydrazine synthase complex	Protein complex	part of	Reviewed label only (reviewed name; no accession asserted)	hzsA, hzsB, hzsC	ESSENTIAL	Anammoxosome lumen enzyme complex that condenses nitric oxide and ammonium-derived reducing equivalents to hydrazine. `DOI:10.1128/JB.00186-15` Kartal et al. 2015 immunolocalized hydrazine synthase subunits to the anammoxosome of Candidatus Kuenenia stuttgartiensis. `DOI:10.1111/1574-6976.12014` Kartal et al. 2013 review hydrazine synthase as the central hydrazine-forming complex of anammox catabolism.
hydrazine dehydrogenase and hydroxylamine oxidoreductase-family cytochromes	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	hdh, hao	ESSENTIAL	Octaheme cytochromes in the anammoxosome that oxidize hydrazine to dinitrogen and recycle electrons to the pathway. `DOI:10.1128/JB.00186-15` Kartal et al. 2015 localized hydroxylamine oxidoreductase-family proteins to the Candidatus Kuenenia stuttgartiensis anammoxosome. `DOI:10.1111/1574-6976.12014` Kartal et al. 2013 review hydrazine dehydrogenase and related octaheme cytochromes in the anammox pathway.
anammoxosome electron-transfer proteins	Protein	part of			UNKNOWN	Membrane-associated cytochromes and quinone-linked proteins that recycle electrons among nitrite reduction, hydrazine synthesis and hydrazine oxidation. `DOI:10.1111/1574-6976.12014` Kartal et al. 2013 review the proposed anammoxosome electron-transport loop linking hydrazine oxidation back to nitrite and nitric oxide reduction.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

hydrazine dehydrogenase and hydroxylamine oxidoreductase-family cytochromes

Accession	Protein	Gene	Organism	Entry
`UniProtKB:Q1PX48`	Hydroxylamine oxidoreductase	hao	Candidatus Kuenenia stuttgartiensis (`NCBITaxon:174633`)	REVIEWED
Role and evidence (1 reference) UniProt annotates this protein to SL-0491 (anammoxosome); component role: Octaheme cytochromes in the anammoxosome that oxidize hydrazine to dinitrogen and recycle electrons to the pathway. `PMID:25962914` de Almeida NM et al. 2015, ‘Immunogold Localization of Key Metabolic Enzymes in the Anammoxosome and on the Tubule-Like Structures of Kuenenia stuttgartiensis.’, J Bacteriol. ECO:0000269 experimental evidence for the anammoxosome localisation of Q1PX48, as cited by UniProt.

Taxonomic distribution

NCBITaxon:203682 Planctomycetota — RARE: Anammoxosomes are restricted to anaerobic ammonium-oxidizing planctomycetes within the Brocadiales rather than all Planctomycetota. [DOI:10.1111/1574-6976.12014]
NCBITaxon:2 Bacteria — RARE: The organelle has only been described in anammox bacteria. [DOI:10.1111/1574-6976.12014]

Canonical examples

NCBITaxon:174633 Candidatus Kuenenia stuttgartiensis — Model anammox bacterium used for immunogold localization of hydrazine synthase and hydroxylamine oxidoreductase-family proteins in the anammoxosome. [DOI:10.1128/JB.00186-15]

Functions

anaerobic ammonium oxidation — The anammoxosome compartmentalizes the conversion of ammonium and nitrite through nitric oxide and hydrazine intermediates to dinitrogen gas.
- DOI:10.1111/1574-6976.12014 Kartal et al. 2013 review anaerobic ammonium oxidation as the energy metabolism that occurs in the anammoxosome.
energy conservation — Anammoxosome membrane reactions couple hydrazine oxidation and electron transfer to proton motive force generation across the organelle membrane.
- DOI:10.1111/1574-6976.12014 Kartal et al. 2013 review the proposed anammoxosome proton motive force generated by pathway electron transport.

Mechanism graphs

Hydrazine metabolism is localized inside a ladderane-bounded organelle (FUNCTION)

The ladderane membrane bounds an anammoxosome lumen enriched for hydrazine synthase and HAO-family cytochromes. Nitrite-derived nitric oxide and ammonium are converted to hydrazine, hydrazine is oxidized to dinitrogen, and electrons recycle through membrane-associated carriers that support energy conservation.

Subject	Predicate	Object	Evidence
ladderane lipid membrane	bounds	anammoxosome	`DOI:10.1111/1574-6976.12014` Kartal et al. 2013 review ladderane lipids as the signature anammoxosome membrane lipids.
hydrazine synthase complex	condenses	ammonium	`DOI:10.1111/1574-6976.12014` Kartal et al. 2013 review hydrazine synthase as the enzyme that makes hydrazine from nitric oxide and ammonium-derived electrons.
hydrazine synthase complex	reduces	nitric oxide	`DOI:10.1111/1574-6976.12014` Kartal et al. 2013 place nitric oxide between nitrite reduction and hydrazine synthesis in the anammox pathway.
hydrazine synthase complex	produces	hydrazine	`DOI:10.1128/JB.00186-15` Kartal et al. 2015 localized HZS to the anammoxosome where hydrazine metabolism is proposed to occur.
hydrazine dehydrogenase	oxidizes	hydrazine	`DOI:10.1111/1574-6976.12014` Kartal et al. 2013 review hydrazine oxidation to dinitrogen by hydrazine dehydrogenase in the anammoxosome.
hydrazine dehydrogenase	feeds electrons to	anammoxosome electron-transfer proteins	`DOI:10.1111/1574-6976.12014` Kartal et al. 2013 describe an electron-transport loop that recycles electrons from hydrazine oxidation toward nitrite reduction and hydrazine synthesis.
anammoxosome electron-transfer proteins	localize to	anammoxosome	`DOI:10.1128/JB.00186-15` Kartal et al. 2015 immunolocalized key anammox enzymes in the anammoxosome and on tubule-like structures.

Discussions

CURATION_TODO (OPEN): Resolve exact HZS, HDH, HAO and membrane electron-transfer complex identities from Kuenenia proteomics and structures, then split or ground the grouped anammox enzyme components accordingly. The first organelle record captures localised enzyme classes but does not yet distinguish every paralogous octaheme cytochrome or quinone-linked carrier in the anammoxosome membrane.

Evidence

DOI:10.1111/1574-6976.12014 Kartal B, de Almeida NM, Maalcke WJ, Op den Camp HJM, Jetten MSM and Keltjens JT 2013, How to make a living from anaerobic ammonium oxidation, FEMS Microbiology Reviews.
DOI:10.1128/JB.00186-15 Kartal et al. 2015, Immunogold localization of key metabolic enzymes in the anammoxosome and on the tubule-like structures of Kuenenia stuttgartiensis, Journal of Bacteriology.
PMID:15098544 Sinninghe Damste et al. 2002 identified ladderane lipid membrane components in anammox bacteria.

Curation history

2026-09-04T18:43:10Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-04T19:09:15Z claude · EXPANDED_RECORD — Added anammoxosome lipid and enzyme components, taxonomic scope, Kuenenia example, functions, evidence, a hydrazine-loop graph, and a subcomplex-resolution todo.
2026-09-08T07:38:12Z uniprot_sl · SEED_PROTEIN_EXAMPLES — Added 1 taxon-paired protein example(s) from UniProtKB reviewed entries annotated to SL-0491 (Anammoxosome), matched to components by gene symbol, each carrying UniProt's ECO:0000269 PubMed evidence for the localisation.

Source: data/structures/membrane_organelle/anammoxosome.yaml