amphitrichous

Deep research

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

# Curation-focused research report: amphitrichous

## Record and scope summary

- **Trait:** amphitrichous
- **Identifier:** `traitmech:000059`
- **Category / kind / status:** MORPHOLOGY / CLASS / REVIEWED
- **Parent:** `traitmech:000056`
- **Working definition:** a flagellar arrangement in which flagellar filaments occur at both cell poles. Under the supplied TraitMech definition, either a single filament or a tuft may occupy each pole.

The phenotype is an **observed spatial arrangement**, not merely possession of flagellar genes, swimming ability, polar flagella, or bipolar localization of a regulatory protein. *Campylobacter jejuni* is the best experimentally developed amphitrichous model: it is described as carrying a single flagellum at each pole, although culture populations can contain cells flagellated at only one pole. Reviews also list *Magnetospirillum magneticum* as amphitrichous. (liang2018flhf(t368a)modulatesmotility pages 11-14, grognot2021morethanpropellers pages 4-5)

### Boundary cases

1. **Monotrichous:** one flagellum at one pole; not amphitrichous.
2. **Unipolar lophotrichous:** a tuft at only one pole; not amphitrichous.
3. **Bipolar lophotrichous:** a tuft at each pole, exemplified by *Helicobacter suis*. This satisfies the supplied broad definition but should be qualified as `bipolar_lophotrichous`, because some literature treats it as distinct from amphitrichous sensu stricto, meaning approximately one filament per pole. (grognot2021morethanpropellers pages 5-7, grognot2021morethanpropellers pages 1-2)
4. **Peritrichous:** flagella distributed over the cell surface rather than restricted to both poles. (grognot2021morethanpropellers pages 2-4, schuhmacher2015howbacteriamaintain pages 2-4)
5. **Transient predivision bipolarity:** a normally monotrichous organism may place assembly factors or a nascent flagellum at the future daughter pole before cytokinesis. Neither bipolar FlhF/FipA foci nor this cell-cycle intermediate alone establishes an amphitrichous species-level phenotype. (arroyoperez2024aconservedcellpole pages 12-14, schuhmacher2015howbacteriamaintain pages 4-5)
6. **Motility:** swimming is a functional consequence, not the defining morphology. Nonmotile cells may retain bipolar filaments, while motile cells need not be amphitrichous.

## Current mechanistic understanding

The strongest amphitrichous-specific model combines two layers:

1. **Placement/number control:** the SRP-family GTPase FlhF and MinD-family ATPase FlhG regulate polar flagellar position and number. In amphitrichous *C. jejuni*, loss of `flhF` abolishes flagella, whereas loss of `flhG` produces hyperflagellation; the latter was also associated with minicell/cell-division defects. These observations establish necessity for correct morphology but do not, by themselves, explain how the two poles are selected. (schuhmacher2015howbacteriamaintain pages 5-7)
2. **Assembly-coupled transcription:** FliF, FliG, and the flagellar type III secretion system form an early assembly checkpoint sensed by FlgS. FlgS→FlgR signaling, together with σ54, activates rod and hook transcription; later hook completion permits σ28-dependent filament and motor completion. This pathway is demonstrated directly in amphitrichous *C. jejuni*. (burnham2020apolarflagellar pages 2-4)

Recent 2024 studies refine the physical mechanism for **polar** assembly. In *Shewanella putrefaciens*, FlhF binds the landmark HubP through its NG domain and binds FliG through an N-terminal FliG-interaction domain. FlhF-bound FliG can engage the MS-ring protein FliF while initially excluding FliM/FliN, suggesting a regulated diffusion-capture and assembly-checkpoint mechanism. This is compelling mechanistic evidence for polar localization, but it is not yet direct evidence for selecting both poles in an amphitrichous organism. (dornes2024polarconfinementof pages 2-4, dornes2024polarconfinementof pages 7-8)

A second 2024 study identified FipA as a membrane-associated FlhF partner. FipA promotes FlhF activity and polar accumulation, while FipA and HubP provide partly independent inputs. FipA can exhibit uni- or bipolar localization, but the work used *Vibrio parahaemolyticus*, *Pseudomonas putida*, and *S. putrefaciens*, not a validated amphitrichous model. (arroyoperez2024aconservedcellpole pages 14-15, arroyoperez2024aconservedcellpole pages 12-14)

## Candidate nodes

### Trait and taxon nodes

| Candidate node | Suggested grounding | Curation note |
|---|---|---|
| amphitrichous flagellar arrangement | `traitmech:000059` | Target morphology; preserve identifier verbatim. |
| *Campylobacter jejuni* | `NCBITaxon:197` | Strongest direct mechanistic taxon. Strain-specific experiments should additionally identify PT14, 81-176, or the relevant strain. |
| *Magnetospirillum magneticum* | Label plus verified NCBITaxon ID before use | Morphological example, but the retrieved evidence does not establish the same mechanism. |
| bipolar-lophotrichous *Helicobacter suis* | Label plus verified NCBITaxon ID before use | Boundary/subtype example, not evidence for a universal amphitrichous mechanism. |

### Genes and proteins

| Node | Function in candidate graph | Grounding recommendation |
|---|---|---|
| FlhF | SRP-type GTPase controlling polar placement and assembly | Use gene symbol plus strain-specific UniProt accession only after sequence verification. |
| FlhG/FleN | MinD-like ATPase controlling flagellar number; stimulates FlhF GTPase | Gene symbol; strain-resolved UniProt required. |
| HubP/FimV | Polar landmark binding FlhF | **Uncertain for amphitrichous graph**; demonstrated in other polar systems. |
| FipA/DUF2802 protein | Membrane FlhF partner/pole-licensing factor | **Uncertain and taxon-specific**. |
| FliF | Flagellar MS-ring protein | Component of the assembly checkpoint. |
| FliG | Rotor/C-ring protein and FlhF-binding assembly intermediate | Direct checkpoint role in *C. jejuni*; direct FlhF binding shown in *S. putrefaciens*. |
| FliM and FliN | C-ring switch proteins | Do not merge with FliG; checkpoint requirements differ. |
| FlhA, FlhB, FliP, FliQ, FliR | fT3SS core proteins | Group node is acceptable if individual edges are not needed. |
| FlgS | Sensor histidine kinase detecting assembled MS-ring/rotor/fT3SS | Direct in *C. jejuni*. |
| FlgR | Response regulator activating σ54-dependent genes | Direct in *C. jejuni*. |
| RpoN/σ54 | Sigma factor for rod/hook transcription | Use strain-specific gene/protein grounding. |
| FliA/σ28 and FlgM | Late flagellar transcription factor and anti-sigma factor | Downstream completion module; not specific to bipolar placement. |

Showing the first 60 of 209 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.