bacterial-type flagellum

GO:0009288 · Appendage · Appendage · Proposed

The rotary motility organelle of bacteria: a long helical filament of flagellin joined by a flexible hook to a basal body that spans the cell envelope. The basal body houses a rotor (MS and C rings) driven by membrane-embedded stator units that convert ion flow (H+ or Na+) into torque; the flagellar type III export apparatus at its base secretes the axial subunits. Not homologous to the archaeal archaellum or the eukaryotic cilium. [DOI:10.1146/annurev.biochem.72.121801.161737]

Synonyms: bacterial flagellum

Has part: bacterial-type flagellum filament (GO:0009420); bacterial-type flagellum filament cap (GO:0009421); bacterial-type flagellum hook-filament junction (GO:0009422); bacterial-type flagellum hook (GO:0009424); bacterial-type flagellum basal body (GO:0009425)

Xrefs: uniprot.location:SL-0307 — Bacterial flagellum

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

Components

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.

flagellin (FliC)

hook protein (FlgE)

MS ring (FliF)

C ring / switch complex (FliG, FliM, FliN)

stator unit (MotA5MotB2)

rod (FlgB, FlgC, FlgF, FlgG)

flagellar type III membrane export gate (FlhA, FlhB, FliP, FliQ, FliR)

Taxonomic distribution

• NCBITaxon:2 Bacteria — VARIABLE: Patchy across bacterial lineages. A survey of 30,238 representative genomes across 131 phyla detected conserved FliP/Q/R markers in about 40%; this is genomic evidence of flagellar capacity, not direct observation of assembled flagella or proof of absence in every marker-negative genome. [DOI:10.1073/pnas.2512476122]
• NCBITaxon:2157 Archaea — ABSENT: Archaea swim with the archaellum, a type-IV-pilus-related structure with no homology to the bacterial flagellum. [DOI:10.3389/fmicb.2015.00023]

Canonical examples

• NCBITaxon:90371 Salmonella enterica subsp. enterica serovar Typhimurium — The genetic model for flagellar assembly and export. [DOI:10.1146/annurev.micro.57.030502.090832]
• NCBITaxon:83333 Escherichia coli K-12 — Model for motor physics and chemotaxis. [DOI:10.1146/annurev.biochem.72.121801.161737]
• NCBITaxon:83334 Escherichia coli O157:H7 — Taxon depicted in the hosted TEM; purified H7 flagellar filaments from an O157:H7 isolate were independently characterized by microscopy and immunoassay. [DOI:10.1128/jcm.26.7.1367-1372.1988]
• NCBITaxon:224308 Bacillus subtilis subsp. subtilis str. 168 — SubtiWiki's reference strain and a classical genetic model for flagellar assembly. [DOI:10.1093/nar/gkae957]

Functions

• bacterial-type flagellum-dependent cell motility GO:0071973
  • DOI:10.1146/annurev.biochem.72.121801.161737 Berg 2003 reviews the rotary motor and swimming.

Associated traits

• CONFERS METPO:1000704 flagellated
  • DOI:10.1146/annurev.micro.57.030502.090832 Macnab 2003 reviews assembly of the bacterial flagellar organelle.
• CONFERS METPO:1000702 motile — One of several motility machines; gliding and twitching motility do not use it.
  • DOI:10.1146/annurev.biochem.72.121801.161737 Berg 2003 reviews how rotation of bacterial flagella drives swimming.

Physical properties

• DIAMETER: ~20 UO:0000018 (filament) [DOI:10.1146/annurev.micro.57.030502.090832]
• LENGTH: up to 20 UO:0000017 (filament; upper-length example in a review, not a universal maximum or a taxon-specific measurement)
  • DOI:10.3390/biom11020186 — Around 20,000 subunits of flagellin assemble to form the flagellar filament, which can grow up to a 20 µm in length [ 25 , 75 ]. The cited review supports growth up to 20 micrometers, not a lower limit of 5. The unsupported minimum has been removed; no universal size range is inferred.
• ROTATION_SPEED: ~100-300 UO:0000092 (Escherichia coli motor; ~125 Hz at high load with the filament attached, 300 Hz or faster at low load)
  • DOI:10.1128/jb.00353-25 — When attached to the flagellar filament (high load), E. coli motors spin at ~125 Hz; when the filament is absent (low load), motors rotate at 300 Hz or faster ( 27 , 28 ). Verbatim from the open-access full text (PMC12713396). This corrects the record: the context previously attributed the whole 100-300 Hz range to light load, but the lower figure is the high-load value and only the upper is low-load. Replaces the Berg 2003 review, which is abstract-only and does not contain the numbers (#171).

Mechanism graphs

Ion flow through the stator turns the rotor and the filament (FUNCTION)

Discussions

• CURATION_TODO (OPEN): Resolve exact source-neutral family or complex groundings for the MS ring, C ring, stator, rod, LP rings and membrane export gate. Groundings were deliberately left blank rather than guessed; verify each accession against InterPro before adding.

Evidence

• DOI:10.1146/annurev.biochem.72.121801.161737 Berg 2003, "The rotary motor of bacterial flagella".
• DOI:10.1146/annurev.micro.57.030502.090832 Macnab 2003, "How bacteria assemble flagella".
• DOI:10.1038/nrmicro1887 Chevance & Hughes 2008, "Coordinating assembly of a bacterial macromolecular machine".

Curation history

• 2026-08-29T00:00:00Z claude · CREATED_RECORD — Drafted composition, distribution, trait links and torque-generation mechanism graph from the cited reviews and stator structures. Not yet human-reviewed.
• 2026-08-29T03:00:00Z claude · ADD_IMAGE — Added Commons image File:Escherichia_coli_flagella_TEM.png (public domain, CDC PHIL, NCBITaxon:83334); no publication, per decision #30. Added E. coli O157:H7 to taxonomic_distribution as the imaged strain.
• 2026-08-30T02:14:17Z uniprot_sl · ADD_UNIPROT_SL_XREF — Added uniprot.location:SL-0307 (Bacterial flagellum); mapping read from the GO line of UniProt subcell.txt.
• 2026-08-30T19:08:55Z fetch_commons_image · ADD_IMAGE — Updated Commons image File:Escherichia_coli_flagella_TEM.png (PUBLIC_DOMAIN, Escherichia coli O157:H7); licence, attribution and taxon read from the Commons and Wikidata APIs at retrieval.
• 2026-08-30T19:11:12Z fetch_commons_image · ADD_IMAGE — Updated Commons image File:Escherichia_coli_flagella_TEM.png (PUBLIC_DOMAIN, Escherichia coli O157:H7); licence, attribution and taxon read from the Commons and Wikidata APIs at retrieval.
• 2026-08-30T19:29:55Z codex · REVIEW_EVIDENCE_AND_ESSENTIALITY — Corrected MotA/MotB stator essentiality from ESSENTIAL to DISPENSABLE using deletion-mutant imaging; changed rotation speed from generic hertz to UO turns per second; added evidence to both trait links; removed the hosted-image strain from clade-level taxonomic distribution; and replaced the silently truncated Commons credit with a complete provenance summary.
• 2026-08-30T19:38:35Z codex · REVIEW_TAXONOMIC_SCOPE — Removed Escherichia coli O157:H7 from taxonomic_distribution because a hosted image establishes an observed specimen, not universal presence across the strain; the image retains its own taxon provenance.
• 2026-08-30T19:40:01Z codex · DOCUMENT_IMAGE_EXEMPLAR — Added the hosted-image O157:H7 taxon as a cited canonical example rather than overstating it as a universally flagellated taxonomic scope.
• 2026-08-31T06:03:17Z claude · APPLY_COMPONENT_BOUNDARY — Component-boundary rule (#66, #72): stated in the stator role that DISPENSABLE here means 'not needed for assembly', not 'peripheral machinery'.
• 2026-08-31T06:12:34Z claude · SET_COMPONENT_ROLE — component_role became required (#77) so the constituent/machinery distinction is machine-readable rather than prose. Set per component; ASSOCIATED_MACHINERY only where the protein acts on the already-assembled structure.
• 2026-09-02T04:28:37Z subtiwiki · SEED_PROTEIN_EXAMPLES — Added or refreshed 17 curator-reviewed B. subtilis flagellar protein examples from SubtiWiki category 387; exact gene ids and UniProt outlinks were checked at SubtiWiki, then reviewed status, gene identity and taxon were checked independently at UniProtKB; FliY C-ring and MotP/MotS stator placements were independently literature-backed. No SubtiWiki prose, sequences or bulk export was copied.
• 2026-09-02T05:45:19Z interpro_groundings · GROUND_COMPONENTS — Applied exact integrated InterPro family groundings to flagellin; recorded label-only decisions for none. The fixed reviewed allow-list required exact component identity, reviewed UniProt examples, type=family entries, and unchanged family consensus across curated scope examples.
• 2026-09-03T00:37:47Z claude · RESOURCE_CLAIMS — #7 item 5 and #171: the ~20,000 flagellin figure, the 11 protofilaments, the filament length and the motor rotation speed all cited reviews that are abstract-only and do not contain the numbers. Each is now sourced to open-access full text with a verbatim quotation. Two corrections fell out of reading: the rotation-speed context wrongly attributed the whole 100-300 Hz range to light load, when ~125 Hz is the high-load figure; and the 11-protofilament claim is not universal, since Campylobacter jejuni has seven. The filament DIAMETER remains unsourced -- no open-access source stating it was found -- and is left for the human review track.
• 2026-09-03T07:37:09Z interpro_groundings · GROUND_COMPONENTS — Applied exact integrated InterPro family groundings to none; recorded label-only decisions for hook. The fixed reviewed allow-list required exact component identity, reviewed UniProt examples, type=family entries, and unchanged family consensus across curated scope examples.
• 2026-09-03T07:41:11Z interpro_groundings · GROUND_COMPONENTS — Applied exact integrated InterPro family groundings to none; recorded label-only decisions for hook. The fixed reviewed allow-list required exact component identity, reviewed UniProt examples, type=family entries, and unchanged family consensus across curated scope examples.
• 2026-09-04T01:40:08Z codex · ENHANCE_CAUSAL_GRAPH — Added descriptions to the remaining flagellar torque-generation edges so every edge now states the mechanistic step it represents.
• 2026-09-08T06:56:10Z claude · ADDRESS_REVIEW — Resolved #268 by renaming the five-protein flagellar export aggregate as the membrane export gate rather than the full ATPase-associated secretion apparatus.
• 2026-09-08T07:51:38Z uniprot_genes · SEED_PROTEIN_EXAMPLES — #183: added 3 protein example(s) by resolving each of the component's declared gene symbols to the single reviewed UniProtKB entry for that symbol in a taxon this record names, deduplicated by accession. Symbols resolving to more than one reviewed entry were skipped rather than chosen between.
• 2026-09-09T02:35:39Z claude · ADD_SUBSTRUCTURE_LINK — Added the GO:0009422 bacterial-type flagellum hook-filament junction record to the top-level bacterial-type flagellum has_part list.
• 2026-09-09T04:27:53Z claude · ADDRESS_REVIEW — Resolved #289 by adding GO:0009421 as a direct has_part of the enclosing bacterial-type flagellum after moving the FliD/HAP2 cap out of the GO:0009420 filament boundary.
• 2026-10-10T20:21:31Z claude · ADDRESS_REVIEW — Addressed #2128, #2129, #2130, #2131, #2132, #2133: Remove the unsourced flagellar filament length minimum; Qualify proposed stator rotation in three flagellar records; Distinguish proton and sodium motive forces in the flagellum graph; Correct bacterial flagellum and basal-body prevalence scope; Qualify C-ring assembly essentiality in the enclosing flagellar records; Narrow the completed portions of the flagellum grounding TODO.

Source: data/structures/appendage/bacterial_type_flagellum.yaml