sphere shaped

Deep research

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

# Curation report: sphere-shaped microbial morphology

## Target and scope

- **Trait:** sphere shaped
- **Identifier:** **METPO:1000683**
- **Category/kind:** MORPHOLOGY / CLASS
- **Parent:** METPO:1000666
- **Operational meaning:** a cell whose three principal dimensions are approximately equal. For curation, this should mean a stable single-cell geometry under specified growth conditions, not merely the taxonomic descriptor “coccus.”

The strongest general mechanism is spatially restricted cell-wall growth. Peptidoglycan (PG) forms a closed sacculus that preserves cell geometry; its enlargement is governed by localized synthesis and hydrolysis rather than by the sacculus encoding shape autonomously. Elongasomes mediate peripheral growth, whereas divisomes mediate septal growth. Suppressing lateral elongation while retaining division-centered PG synthesis is therefore a recurrent route toward coccal geometry. However, this is a mechanistic pattern, not a universal rule: spherical taxa can use distinct division systems, and ovococci retain appreciable peripheral synthesis. (caccamo2018themolecularbasis pages 1-2, egan2020regulationofpeptidoglycan pages 1-2, teeseling2017determinantsofbacterial pages 3-4)

### Boundary cases

1. **Ovoid/ovococcal cells are not spherical.** *Streptococcus pneumoniae* and *S. suis* undergo both peripheral and septal PG synthesis near midcell; their long and short axes remain distinguishable. Nanoscale imaging showed that pneumococcal septal and peripheral syntheses begin in one annular region, later separate into concentric regions, and that peripheral synthesis persists after septation. (jiang2023divivainteractswith pages 1-2, trouve2021nanoscaledynamicsof pages 1-3)
2. **“Coccoid” is broader than “sphere-shaped.”** It can include nearly spherical, ovoid, irregular, or conditionally rounded cells. A curation assertion should preferably include quantitative length, width, aspect ratio, circularity, or three-dimensional reconstruction.
3. **Wall-deficient forms are a separate mechanism.** L-forms and dormant wall-deficient cells round because membrane mechanics dominate after PG loss; they should not establish a constitutive sphere-shaped trait. (caccamo2018themolecularbasis pages 1-2, carvalho2024aquaticenvironmentdrives pages 1-2)
4. **Transient mutant rounding is evidence about a mechanism, not necessarily trait possession.** For example, reduced peripheral PG synthesis makes *S. suis* shorter and wider, but this demonstrates movement toward roundness rather than conversion to a validated sphere. (jiang2023divivainteractswith pages 7-9)
5. **Cell clusters must be separated from cell shape.** The grape-like appearance of *S. aureus* results from perpendicular division planes and delayed daughter separation; the individual cells, not the cluster, are spherical. (bartlett2023identificationoffacz pages 1-5)

## Current mechanistic model

The most defensible graph backbone is:

**lipid II production → PG polymerization/cross-linking → PG sacculus → maintenance of cell geometry**

with two spatial branches:

- **MreB/elongasome → peripheral PG synthesis → anisotropic elongation → opposes spherical geometry**;
- **FtsZ/divisome → septal PG synthesis → division-centered envelope growth → supports coccal geometry when lateral elongation is absent or small.**

This formulation is preferable to the absolute statement that all cocci synthesize PG only at the septum. Modern imaging shows that some cocci and especially ovococci have peripheral or periseptal synthesis. In spherical *S. aureus*, envelope biogenesis is principally focused at the division site, but “principally” should not be converted into “exclusively” without species- and assay-specific primary evidence. (bartlett2023identificationoffacz pages 1-5, gaifas2024combininglivecell pages 1-4, trouve2021nanoscaledynamicsof pages 1-3)

## Candidate nodes grouped by type

### Trait and taxon/context nodes

- **sphere shaped — METPO:1000683**
- sphere-shaped cell; coccal morphology; rod-to-coccus transition; increased roundness; cell aspect ratio
- *Staphylococcus aureus* — **NCBITaxon:1280**
- *Streptococcus pneumoniae* — **NCBITaxon:1313**; boundary case: ovococcus
- *Streptococcus suis* — **NCBITaxon:1307**; boundary case: ovococcus
- *Listeria monocytogenes* — **NCBITaxon:1639**; conditional CWD/VBNC boundary case
- *Escherichia coli* — **NCBITaxon:562**; surrogate/perturbation context
- *Chlamydia trachomatis* — **NCBITaxon:813**; noncanonical FtsZ-independent system
- *Deinococcus radiodurans* — **NCBITaxon:1299**; taxon-specific septation geometry

### Structures and cellular locations

- peptidoglycan sacculus
- cytoplasmic membrane
- cell wall; septum/cross-wall; division site; midcell; cell periphery/periseptum
- Z-ring; divisome; elongasome
- opposing septa in *D. radiodurans*

Suggested GO grounding, subject to ontology-version verification before YAML insertion:

- **GO:0007049** — cell cycle
- **GO:0051301** — cell division
- **GO:0000917** — barrier septum assembly

Showing the first 60 of 254 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.