identifier: traitmech:000119 label: tetrad arrangement definition: A cell arrangement in which cocci divide in two perpendicular planes and remain attached as groups of four (tetrads). definition_source: DOI:10.1128/MMBR.00001-06 trait_category: MORPHOLOGY term_kind: CLASS mapping_status: REVIEWED parent_traits: - METPO:1000666 synonyms: - synonym_text: tetrad-forming cocci synonym_type: RELATED_SYNONYM source: DOI:10.1128/MMBR.00001-06 evidence: - reference: DOI:10.1128/MMBR.00001-06 notes: Young's review treats the tetrad as a division-plane-determined coccal arrangement. - reference: DOI:10.1038/ncomms4842 notes: Two-plane division with incomplete daughter-cell separation yields four-cell tetrads. canonical_examples: - taxon_id: NCBITaxon:1270 taxon_label: Micrococcus luteus note: "tetrad/packet cocci" reference: PMID:2325580 - taxon_id: NCBITaxon:1377 taxon_label: Aerococcus viridans note: "tetrad-forming coccus" reference: PMID:25919289 causal_graphs: - graph_id: tetrad_two_plane_division title: Tetrad arrangement via two-plane perpendicular division description: Evidence-backed causal sketch linking division in two perpendicular planes with incomplete separation to four-cell tetrads. nodes: - node_id: tetrad_trait label: tetrad arrangement node_type: TRAIT grounding: traitmech:000119 description: Cocci attached as groups of four (tetrads). - node_id: cell_division label: cell division node_type: BIOLOGICAL_PROCESS grounding: GO:0051301 description: Bacterial binary fission. - node_id: two_plane_perpendicular_division label: two perpendicular division planes node_type: QUALITY description: Successive division planes oriented perpendicular to each other. - node_id: ftsz_z_ring label: FtsZ Z-ring assembly node_type: GENE_OR_PROTEIN description: FtsZ polymerizes into a Z-ring that scaffolds the divisome at the division site. - node_id: septation label: division septum assembly node_type: BIOLOGICAL_PROCESS description: Assembly of the septal cell-wall and membrane between daughter cells. grounding: GO:0000917 - node_id: cell_wall_hydrolases label: cell wall hydrolases (autolysins) node_type: GENE_OR_PROTEIN description: Peptidoglycan hydrolases/autolysins that cleave the septal cell wall to separate daughter cells. - node_id: daughter_cell_splitting label: daughter-cell splitting node_type: BIOLOGICAL_PROCESS description: Rapid physical separation of daughter cells following septation. edges: - subject: two_plane_perpendicular_division predicate: causes object: tetrad_trait description: Two perpendicular division planes with incomplete daughter separation yield four-cell tetrads. evidence: - reference: DOI:10.1038/ncomms4842 notes: Two-plane division with incomplete daughter-cell separation yields four-cell tetrads. predicate_id: biolink:causes - subject: cell_division predicate: enables object: tetrad_trait description: Bacterial cell division underlies tetrad formation. evidence: - reference: DOI:10.1128/MMBR.00001-06 notes: Young treats the tetrad as a division-plane-determined coccal arrangement. predicate_id: RO:0002327 - subject: ftsz_z_ring predicate: scaffolds object: septation description: FtsZ assembles into a Z-ring that scaffolds the divisome and initiates septation. evidence: - reference: DOI:10.1042/bst20240956 notes: FtsZ polymerizes into a Z-ring that scaffolds membrane-associated division factors, forming the divisome that drives septation. - subject: septation predicate: precedes object: daughter_cell_splitting description: Septum assembly precedes the splitting step that physically separates daughter cells. evidence: - reference: DOI:10.1042/bst20240956 notes: After septation the cell splits into two daughter cells; splitting is a distinct, very fast step following septation. - subject: cell_wall_hydrolases predicate: mediates object: daughter_cell_splitting description: Cell wall hydrolases/autolysins cleave septal peptidoglycan to drive rapid daughter-cell splitting. evidence: - reference: DOI:10.1042/bst20240956 notes: After septation the cell splits into two daughter cells very fast (within milliseconds) and requires the actions of cell wall hydrolases. - subject: daughter_cell_splitting predicate: prevents object: tetrad_trait description: Incomplete or delayed daughter-cell splitting after two-plane division leaves cells attached as four-cell tetrads. evidence: - reference: DOI:10.1042/bst20240956 notes: Tetrads arise when a spherical cell divides in one plane and then again in a perpendicular plane, producing four cells arranged as a square due to incomplete separation; failure to complete splitting yields the tetrad. predicate_id: RO:0002212 curation_history: - timestamp: '2026-06-08T00:00:00Z' curator: claude action: PROPOSED_FROM_RESEARCH changes: Proposed candidate MORPHOLOGY trait (tetrad arrangement); leftover round, cell-arrangement sibling of diplococcus shaped. llm_assisted: true - timestamp: '2026-06-09T15:00:00Z' curator: claude action: CURATED_CAUSAL_GRAPH changes: Added evidence-backed causal graph (two-plane perpendicular division → tetrad) with GO node grounding and RO/biolink predicate groundings; promoted PROPOSED to REVIEWED. llm_assisted: true - timestamp: '2026-06-23T00:00:00Z' curator: claude action: ENRICH_CAUSAL_GRAPH changes: Added 4 evidence-backed generic edges (4 new nodes) from the deep-research report. llm_assisted: true - timestamp: '2026-06-24T17:21:14Z' curator: claude action: GROUND_CAUSAL_PREDICATES changes: Grounded 1 causal-edge predicate_id field(s) via mappings/predicate_grounding.tsv (RO:0002212×1). llm_assisted: true - timestamp: '2026-06-24T17:23:34Z' curator: claude action: GROUND_CAUSAL_NODES changes: Grounded 1 causal-node grounding field(s) via mappings/node_grounding.tsv (GO:0000917×1). llm_assisted: true