flask shaped

Deep research

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

# Curation report: microbial “flask shaped” morphology

## Executive assessment

**Target:** `METPO:1000675` (“flask shaped”; morphology class; reviewed). The trait denotes a **cell-body geometry** with a bulbous body narrowing into a neck-like extension at one pole. In the literature, the closest operational descriptors are **pear-shaped**, **tear-drop-shaped**, or a cell with one rounded pole and one tapered pole.

The strongest mechanistic model is not yet a direct knockout-to-flask-shape pathway in a canonical flask-shaped planctomycete. Rather, it is a taxon-specific model from the stalked budding alphaproteobacterium *Hyphomonas neptunium*: cell-cycle-regulated switching among dispersed and zonal peptidoglycan (PG) insertion sites generates an asymmetric cell with a rounded old pole and tapered new/stalked pole. By contrast, deletion of `mreB`, `ftsI`, or `ftsW` in pear-shaped *Planctopirus limnophila* caused no observable phenotype under the tested conditions, arguing against importing the *H. neptunium* pathway wholesale into Planctomycetota (cserti2017dynamicsofthe pages 7-9, cserti2017dynamicsofthe pages 4-7, wiegand2020cultivationandfunctional pages 5-6).

The user-supplied DOI `10.1146/annurev-cellbio-101011-155745` is **not a bacterial cell-shape review**; it resolves to Lamkanfi and Dixit’s 2012 review, *Inflammasomes and Their Roles in Health and Disease*. It should therefore be removed from the existing causal graph unless a different DOI was intended.

## 1. Trait scope and boundaries

### Included phenotype

A cell should be annotated `METPO:1000675` when microscopy shows:

- a conspicuously bulbous or rounded main body;
- unilateral narrowing toward one pole;
- a neck-like or tapered polar region;
- a stable or developmentally defined pear/tear-drop/flask outline.

In *H. neptunium*, newborn cells were quantitatively asymmetric, with a round old pole and tapered new pole; the reported round:tapered pole-curvature ratio was **0.4 ± 0.1 (n = 10)**. The stalk diameter was **131 ± 3 nm (n = 50)**, with an internal cytoplasmic space of **60 ± 2 nm (n = 50)** (cserti2017dynamicsofthe pages 7-9).

### Boundary cases

1. **Pear- or tear-drop-shaped:** normally include when the main body narrows unilaterally. *P. limnophila* is explicitly described as pear-shaped and is a strong positive exemplar (wiegand2020cultivationandfunctional pages 5-6).
2. **Stalked/prosthecate:** do not equate a stalk with flask shape. A rod or coccus may bear a stalk without having a bulbous, tapered body.
3. **Budding:** budding is a division mode, not a shape. The 2020 survey observed budding in both elongated and coccoid cells; therefore, budding is neither necessary nor sufficient for flask morphology (wiegand2020cultivationandfunctional pages 5-6).
4. **Ovoid:** include only when one pole is demonstrably narrower; a symmetric oval lacks the defining neck-like polarity.
5. **Pyriform:** often compatible, but image-level review is advisable because taxonomic descriptions use “pyriform” inconsistently.
6. **Pleomorphic/amoeboid/shapeshifting:** exclude unless a reproducible flask-shaped state is explicitly observed. The absence of a rigid stable outline is a different phenotype.
7. **Flask culture:** exclude lexical matches in which “flask” describes a vessel rather than cell morphology.

## 2. Current mechanistic understanding

PG is the primary structural polymer that maintains bacterial shape. Planctomycetota were historically claimed to lack PG, but biochemical assays, isolated sacculi, lysozyme sensitivity, microscopy, and cryo-electron tomography demonstrated a typical PG wall in representatives including *Planctopirus limnophila*. The authors explicitly characterize PG as critical for maintenance of shape and division (jeske2015planctomycetesdopossess pages 1-2).

In *H. neptunium*, flask/pear-like polarity emerges from a **spatiotemporal morphogenetic program** rather than from a single dedicated “flask-shape gene.” HADA labeling revealed sequential PG incorporation throughout the swarmer body, at the new pole/stalk base, throughout the stalk during bud initiation, in the nascent bud, and finally at the bud neck. The authors conclude that morphology is determined by multiple cell-cycle-regulated zones of dispersed and zonal PG growth (cserti2017dynamicsofthe pages 7-9).

The MreB-controlled elongasome and PBP2 are critical in this organism. This differs from polarly growing Rhizobiales, which commonly lack MreB, MreCD, RodA, RodZ, and PBP2. Thus, “polar growth” is mechanistically heterogeneous across bacterial lineages and should be represented by taxon-qualified subgraphs rather than one universal pathway (cserti2017dynamicsofthe pages 4-7).

## 3. Candidate nodes

### Trait and organism nodes

- **flask shaped** — `METPO:1000675`
- pear-shaped cell — label-only synonym/near-equivalent pending ontology review
- tapered cell pole — label-only
- bulbous cell body — label-only
- *Hyphomonas neptunium* — use a verified NCBITaxon identifier during implementation
- *Planctopirus limnophila* — use a verified NCBITaxon identifier during implementation
- Planctomycetota — taxonomic context node; verify current NCBITaxon CURIE

### Structural and localization nodes

- peptidoglycan — `CHEBI:8005`
- peptidoglycan-based cell wall — `GO:0009274`
- cell wall — `GO:0005618`
- cell pole — `GO:0060187`
- new/tapered pole — label-only

Showing the first 60 of 239 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.