twitching motility

Deep research

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

# Curation report: twitching motility

## Trait record and scope

- **Trait:** twitching motility
- **Identifier:** `traitmech:000061`
- **Category / kind / status:** MORPHOLOGY / CLASS / REVIEWED
- **Parent:** `METPO:1000702`
- **Synonym:** twitching

Twitching motility is flagellum-independent crawling over a moist solid surface or solid–medium interface. A surface-exposed type IV pilus (T4P) extends, its tip or filament attaches to the substratum, and retraction pulls the cell toward the attachment point. Repetition produces intermittent, jerky translocation. This “extension–attachment–retraction” cycle is the defining mechanism, not merely the presence of pili or surface spreading. Mattick’s foundational review identifies pilus retraction as the motive force and describes the characteristic intermittent jerks and directional changes; a later mechanosensing review states explicitly that repeated extension, attachment, and retraction pull the cell body forward (mattick2002typeivpili pages 5-7, webster2022thepowerof pages 10-12).

### Inclusion criteria

Curate a positive phenotype when there is evidence of:

1. translocation along a solid or interfacial surface;
2. dependence on retractile T4P or homologous type-IV filaments;
3. force-producing pilus attachment and retraction; and
4. an assay measuring interface expansion or individual-cell displacement.

Common assays include a subsurface stab inoculation followed by radial expansion at an agar–plastic interface, colony-edge imaging in glass–agarose sandwiches, and direct single-cell or single-pilus imaging. Surface attachment is a mechanistic prerequisite, so planktonic movement should not be called twitching (tala2022characterizationofpseudomonas pages 58-61, geiger2024abacterialsense pages 3-5, tala2022characterizationofpseudomonas pages 56-58).

### Boundary cases

- **Swimming:** propulsion in liquid by rotating flagella; exclude.
- **Swarming:** coordinated surface migration that is usually flagellum-dependent and often surfactant-assisted; exclude unless T4P-dependent single-cell twitching is measured separately.
- **Sliding:** passive, growth- and surface-force-driven colony spreading without a dedicated motility motor; exclude. A T4P/flagellum-deficient *Pseudomonas aeruginosa* colony can therefore spread without exhibiting twitching.
- **Gliding:** a broad surface-motility label covering several unrelated mechanisms. *Myxococcus xanthus* “social gliding” is T4P-dependent and mechanistically equivalent to twitching, whereas adventurous/non-T4P gliding is outside scope (mattick2002typeivpili pages 5-7).
- **Adhesion, natural transformation, secretion, and biofilm formation:** T4P can mediate all of these without twitching. They are associated functions, not evidence of the motility phenotype by themselves.
- **Pilus extension without productive retraction:** insufficient. Hyperpiliation can coexist with loss of twitching.

## Current mechanistic model

PilA major pilin subunits form the fiber. The PilB ATPase supplies energy for polymerization and extension through the PilC platform; the filament exits the outer membrane through the PilQ secretin. Once attached, PilT-driven depolymerization retracts the fiber. PilU can augment PilT-dependent retraction, especially under high load. Retraction converts ATP-derived mechanical work into cell-body displacement; repeated cycles produce the trait (tala2022characterizationofpseudomonas pages 56-58, tala2022characterizationofpseudomonas pages 21-24, webster2022thepowerof pages 10-12).

This simple “grappling hook” description remains useful, but modern imaging shows coordinated attachment sensing and motor switching rather than indiscriminate extension and retraction. In *P. aeruginosa*, attachment can trigger motor engagement within approximately 130–150 ms. Retraction-associated tension substantially prolongs pilus–surface adhesion: one imaging study reported median/characteristic dwell values of about 75 ms in a non-retracting `pilT` mutant versus 2,315 ms in wild type (tala2022characterizationofpseudomonas pages 58-61).

## Candidate nodes

### Trait and process nodes

- twitching motility — `traitmech:000061`
- type IV pilus-dependent motility — label-only unless the project has a validated GO/METPO mapping
- type IV pilus assembly
- type IV pilus extension
- type IV pilus attachment to surface
- type IV pilus retraction
- pilus depolymerization
- cell-body displacement across surface
- directional twitching / T4P-mediated chemotaxis — regulatory subtype, not synonymous with baseline twitching
- surface sensing and surface adaptation — associated processes, not part of the minimal phenotype

### Structural and localization nodes

- type IV pilus / type IVa pilus complex
- PilA-based pilus filament
- PilC assembly platform
- PilQ outer-membrane secretin
- bacterial cell pole

Showing the first 60 of 223 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.