peritrichous

Deep research

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

# Curation report: peritrichous flagellation

## Trait record and scope

- **Trait:** peritrichous
- **Identifier:** `traitmech:000060`
- **Category / kind / status:** MORPHOLOGY / CLASS / REVIEWED
- **Parent:** `traitmech:000056`
- **Operational definition:** a cell-level flagellation pattern in which multiple external flagella are distributed over the cell body rather than restricted to one or both poles.

The best-supported exemplars are *Escherichia coli* and *Bacillus subtilis*. A major review describes these organisms as having approximately **5–6 flagella**, while emphasizing that number varies with growth conditions and cell-cycle state. The pattern is reproduced across division, although *E. coli* flagella are not perfectly uniform: they are uncommon at the extreme poles and may be denser toward the old-pole region. Thus, “surface-distributed” should not be interpreted as mathematically uniform or completely random. (schuhmacher2015howbacteriamaintain pages 4-5, schuhmacher2015howbacteriamaintain pages 2-4)

### Boundary cases

The trait should be distinguished from:

1. **Monotrichous or lophotrichous polar flagellation:** one flagellum or a tuft confined to one pole.
2. **Amphitrichous flagellation:** flagella at both poles.
3. **Periplasmic/endoflagella:** filaments lying between membranes, as in spirochetes; these are not surface-distributed exoflagella.
4. **Inducible lateral flagella:** a second, environmentally regulated flagellar system on the lateral surface in organisms that otherwise carry polar flagella. This is not necessarily constitutive peritrichy.
5. **Hyperflagellation:** increased filament number does not establish peritrichy unless microscopy demonstrates nonpolar surface distribution.
6. **Motility or flagellar-gene presence:** neither swimming nor possession of `fliC` or other assembly genes establishes the spatial morphology.
7. **Aflagellate/nonmotile assay states:** expression is environmentally variable, so absence under one culture condition does not necessarily contradict a species-level capacity for peritrichous flagellation.

Flagellation patterns are species-associated morphologies important for motility, biofilm formation, and pathogenicity, but their underlying placement systems are evolutionarily diverse. Consequently, the graph should not imply that one universal molecular pathway causes all peritrichous patterns. (schuhmacher2015howbacteriamaintain pages 1-2)

## Current mechanistic understanding

The classical *E. coli* model proposed that surface-distributed basal bodies arise largely by stochastic nucleation or “diffusion and capture,” rather than recruitment to a dedicated polar landmark. Nevertheless, inherited asymmetry and old-pole enrichment show that placement is not simply uniform random sampling. As of the major 2015 synthesis, the mechanisms setting flagellar position and number in *E. coli* and *Salmonella* remained poorly understood. (schuhmacher2015howbacteriamaintain pages 4-5, schuhmacher2015howbacteriamaintain pages 2-4)

A major advance appeared after the requested 2023–2024 priority window. Dunn et al. reported in 2025 that nascent *B. subtilis* basal bodies are initially mobile and become immobilized when the flagellar rod assembles through the peptidoglycan. Rod defects increased basal-body mobility, randomized the pattern, and increased polar basal bodies. The authors infer that rod polymerization probes a pre-existing, grid-like organization of sufficiently large peptidoglycan pores. This provides direct support for a physical diffusion-and-capture mechanism in one peritrichous species, but it should not yet be generalized to Enterobacteriaceae. (dunn2025nascentflagellarbasal pages 1-2, dunn2025nascentflagellarbasal pages 17-18)

Recent 2023–2024 FlhF/FlhG studies largely concern polar flagellates. They strengthen the contrast between landmark-mediated polar confinement and distributed assembly but are not direct evidence that those polar mechanisms generate peritrichy. The appropriate expert interpretation is therefore modular: conserved flagellar assembly produces each organelle, whereas separate, taxon-dependent placement and number-control processes generate the peritrichous pattern. (schuhmacher2015howbacteriamaintain pages 9-10, schuhmacher2015howbacteriamaintain pages 1-2)

## Candidate nodes grouped by type

### Phenotypes and processes

- `traitmech:000060` — peritrichous flagellation
- surface-distributed flagellar pattern
- flagellar number control
- flagellar spatial patterning
- basal-body nucleation
- basal-body diffusion and capture
- basal-body immobilization
- flagellar rod polymerization
- bacterial swimming
- chemotaxis
- swarming motility
- initial surface colonization
- biofilm formation

### Cellular structures and localizations

- bacterial-type flagellum
- flagellar basal body
- MS ring
- C ring/switch complex
- flagellar rod
- flagellar hook

Showing the first 60 of 199 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.