spirochete shaped

Deep research

Generated by just research-trait; source: research/traits/morphology/spirochete_shaped-deep-research-falcon.md

# Curation report: **spirochete shaped**

## Target record

- **Trait label:** spirochete shaped
- **Trait identifier:** `METPO:1000693`
- **Category / kind / status:** MORPHOLOGY / CLASS / REVIEWED
- **Parent:** `METPO:1000666`
- **Synonym:** spirochete
- **Working definition:** an elongated spiral, corkscrew-like, or flat-wave cell-body morphology associated with periplasmic flagella situated between the peptidoglycan-bearing cell cylinder and outer membrane.

## 1. Scope and current mechanistic understanding

The trait should denote **whole-cell morphology**, not taxonomic membership in Spirochaetota and not motility alone. The most defensible common mechanism is mechanical coupling between a flexible or rigid peptidoglycan-bearing cell cylinder and internally located periplasmic flagella. The flagella act as both motility organelles and shape-generating cytoskeletal elements. In *Borrelia burgdorferi*, they impose a planar flat-wave form; *Leptospira interrogans* instead has a right-handed helical cylinder with dynamically hook- or spiral-shaped ends; other spirochetes differ in wavelength, handedness, rigidity, and flagellar number. A review reports 7–11 overlapping periplasmic flagella in *B. burgdorferi*, 16–18 in *Brachyspira hyodysenteriae*, but only two non-overlapping flagella in *L. interrogans*. Thus, “tightly coiled helix” is too narrow if the term is intended to include canonical flat-wave *Borrelia*. (nakamura2020spirocheteflagellaand pages 1-3)

In *B. burgdorferi*, flagellar bundles originate subterminally at both poles and extend inward between the cell cylinder and outer membrane. Oppositely directed bundle rotation produces backward-propagating waves in the cell body. The primary literature explicitly states that periplasmic flagella are “critical in providing the characteristic flat-wave morphology.” (sal2008borreliaburgdorferiuniquely pages 1-2)

Cryo-electron tomography of *Treponema pallidum* supports a complementary envelope mechanism: the peptidoglycan layer maintains cell-cylinder integrity and “serves as the interface between the rotating flagella and cell cylinder.” The authors infer that without this layer the fragile cell body could not withstand flagellar friction and torque. This is strong structural-mechanical evidence, but not a peptidoglycan-loss experiment and should therefore be qualified as an inferred interface edge. (liu2010cellulararchitectureof pages 8-9)

### Boundary cases

1. **Generic helical bacteria are not necessarily spirochete-shaped.** Externally flagellated curved or helical bacteria lack the defining periplasmic flagellum–cell-cylinder architecture.
2. **Flat-wave forms belong in scope.** *Borrelia* is described experimentally as flat-wave rather than a tightly coiled cylindrical helix. (sal2008borreliaburgdorferiuniquely pages 1-2)
3. **Flagellar-filament supercoiling is not the target phenotype.** It is an upstream structural state that can deform the cell body.
4. **Hook- and spiral-shaped ends are taxon-specific substates.** These are especially diagnostic of *Leptospira*, not universal spirochete morphology. (wunder2018fcpbisa pages 6-7)
5. **Motility is distinct.** Nonmotility can follow loss of morphology machinery, but an edge to motility does not by itself establish an edge to whole-cell shape.
6. **Cell length, chaining, and failed cytokinesis are distinct phenotypes.** They can accompany flagellar defects without demonstrating loss of helicity.

## 2. Candidate nodes and ontology grounding

### Trait and cellular-structure nodes

- `METPO:1000693` — spirochete shaped.
- Periplasmic flagellum / endoflagellum — use a verified GO cellular-component term if available in the curation environment; otherwise retain as a label-only node rather than assigning an unverified CURIE.
- Flagellar filament; hook; basal body; motor; rotor; stator; spirochete-specific collar.
- Periplasmic flagellar bundle/ribbon.
- Cell cylinder or protoplasmic cylinder.
- Peptidoglycan layer — `GO:0009274` is a candidate GO cellular-component grounding, subject to local ontology validation.
- Periplasmic space — `GO:0042597` is a candidate grounding.
- Outer membrane — `GO:0019867` is a candidate grounding.
- Cytoplasmic membrane — `GO:0005886` is a candidate grounding.
- Flat-wave whole-cell morphology; helical/corkscrew whole-cell morphology; hook-shaped end; spiral-shaped end; rod-shaped loss-of-shape phenotype. These may need label-only or METPO-specific nodes.

### Genes and proteins

- **FlaB:** major flagellin/core-filament protein. Exact gene copies and functions vary by taxon.
- **FlaA:** minor flagellin or filament-associated protein; composition and role vary substantially among spirochetes.
- **FlgE:** flagellar hook structural protein.
- **FcpA:** *Leptospira* flagellar sheath protein.
- **FcpB:** *Leptospira* flagellar-coiling/sheath protein.
- **FlgV / BB0268:** basal-body-associated structural component in *B. burgdorferi*.
- **DnaA:** replication initiator and pleiotropic transcriptional regulator; only an indirect/contextual morphology candidate.
- **CfpA:** treponemal cytoplasmic-filament protein; evidence for a direct conserved shape role remains insufficient.
- **FlbB and collar proteins:** promising *Borrelia*-specific motor/collar nodes, but the retrieved direct evidence was inadequate for a fully resolved edge in the present graph.

Stable protein accessions should be assigned **per species and strain** from UniProt during implementation. A bare symbol such as `flaB` should not be mapped to one universal protein identifier.

### Processes and mechanical states

- Periplasmic flagellum assembly.

Showing the first 60 of 204 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.