cell width

Deep research

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

# Microbial Trait Causal Graph Research Report: Cell Width (METPO:1000882)

## 1. Trait Scope Summary

**Trait:** Cell width (METPO:1000882)  
**Definition:** A phenotype that inheres in a cell by virtue of its shorter dimension when viewed on a plane.  
**Category:** MORPHOLOGY  
**Parent trait:** METPO:1000059

Cell width is the lateral or radial dimension of rod-shaped bacterial cells, perpendicular to the long axis. It is mechanistically distinct from cell length (axial elongation), although both dimensions contribute to overall rod shape and aspect ratio. Width is primarily controlled by the orientation and activity of circumferential peptidoglycan (PG) synthesis machinery, specifically the MreB-directed Rod complex (elongasome). Width excludes processes governing septation, cell division septum thickness, or specialized stalk width in organisms like *Caulobacter crescentus*.

The most direct mechanistic insight is provided by Hussain et al. (2018, DOI:10.1101/197475), who demonstrate that MreB filaments orient along the greatest principal membrane curvature—the circumference of rod-shaped cells—and propose a model where "bacterial width may be specified by opposing actions... a decreasing, 'thinning' activity from the action of MreB and its associated SEDS family PG synthases, and an increasing 'fattening' activity from the non-MreB associated Class A PG synthases" (hussain2017mrebfilamentscreate pages 35-39). This establishes width as a dynamic equilibrium phenotype determined by spatially distinct PG synthesis systems.

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## 2. Candidate Causal Graph Entities

Evidence-backed entities grouped by type are catalogued below with suggested ontology grounding where robust identifiers exist.

### 2.1 Genes, Proteins, Enzymes, Transporters, and Complexes

| Entity | Function/Role | Taxon Context | Suggested Grounding | Notes |
|--------|---------------|---------------|---------------------|-------|
| **MreB** | Bacterial actin homolog; cytoplasmic filament aligning to membrane curvature | *E. coli*, *B. subtilis*, *Salmonella*, *Geobacillus* | Label-only (species-specific IDs not verified) | Central scaffolding protein directing lateral PG synthesis orientation (hussain2017mrebfilamentscreate pages 35-39, morgenstein2015rodzlinksmreb pages 5-6, mao2023ontherole pages 2-3) |
| **RodZ** | Transmembrane linker protein coupling cytoplasmic MreB to periplasmic PG synthesis machinery | *E. coli* | Label-only | Dual role: direct width regulation and mediating MreB rotation; loss increases width (morgenstein2015rodzlinksmreb pages 5-6, ago2023relationshipbetweenthe pages 14-16, morgenstein2015rodzlinksmreb pages 2-4) |
| **RodA (MrdB)** | SEDS-family glycosyltransferase; polymerizes PG glycan strands | *E. coli*, *Salmonella* | Label-only | Forms complex with PBP2; mutations (e.g., RodA^A234T) enhance PG synthesis activity and suppress RodZ defects (ago2023relationshipbetweenthe pages 14-16, ago2023relationshipbetweenthe pages 10-11, ago2023relationshipbetweenthe media c5a06158) |
| **PBP2 (MrdA)** | Class B penicillin-binding protein; transpeptidase crosslinking PG | *E. coli*, *Salmonella* | Label-only | Partner enzyme in RodA-PBP2 synthase; structural opening regulated by interface II contacts and MreC (shlosman2023allostericactivationof pages 2-3, shlosman2023allostericactivationof pages 8-9) |
| **PBP2^SAL** | Homolog of PBP2 expressed under acidic pH | *Salmonella* Typhimurium | Label-only | Forms pH-dependent alternative elongasome independent of canonical PBP2; alters cell dimensions at low pH (castanheira2023evidenceoftwo pages 7-8, castanheira2023evidenceoftwo pages 2-3, castanheira2023evidenceoftwo pages 13-14) |
| **MreC** | Periplasmic Rod complex component | *E. coli*, *Salmonella* | Label-only | Activates RodA-PBP2 by inducing conformational change; suppressor mutations rescue RodZ defects (ago2023relationshipbetweenthe pages 14-16, ago2023relationshipbetweenthe pages 10-11, shlosman2023allostericactivationof pages 2-3) |
| **MreD** | Periplasmic Rod complex component | *E. coli* | Label-only | Function less clear; suppressor mutations also identified (ago2023relationshipbetweenthe pages 14-16, ago2023relationshipbetweenthe pages 10-11) |
| **Rod complex (elongasome)** | Multiprotein assembly including MreB, RodZ, MreC, MreD, RodA, PBP2 | *E. coli*, *Salmonella*, *B. subtilis* | Label-only or GO:0032153 (cell division site) partially relevant | Dynamic, membrane-associated machine inserting lateral PG to maintain rod shape; activity inversely correlates with PG structural defects (ago2023relationshipbetweenthe pages 14-16, ago2023relationshipbetweenthe media c5a06158) |
| **LpxC** | UDP-3-O-acyl-N-acetylglucosamine deacetylase; first committed step in LPS synthesis | *E. coli* | Label-only | Overexpression rescues rod shape in *mreC* hypomorphs by increasing outer membrane stiffness (fivenson2023arolefor pages 3-5, fivenson2023arolefor pages 2-3) |
| **FtsH** | Inner membrane metalloprotease | *E. coli* | Label-only | Degrades LpxC; hypomorphic alleles (e.g., FtsH^V41G) stabilize LpxC and increase LPS, indirectly restoring rod width (fivenson2023arolefor pages 3-5, fivenson2023arolefor pages 2-3) |
| **Class A PBPs (aPBPs)** | Bifunctional PG synthases with glycosyltransferase and transpeptidase domains | Gram-negative bacteria | GO:0008955 (peptidoglycan glycosyltransferase activity) | Proposed "fattening" activity opposing MreB-directed thinning (hussain2017mrebfilamentscreate pages 35-39) |

### 2.2 Chemicals, Metabolites, and Inhibitors

| Entity | Function | Suggested Grounding | Notes |
|--------|----------|---------------------|-------|
| **Peptidoglycan (PG)** | Bacterial cell wall polymer of glycan chains crosslinked by peptide bridges | GO:0009274 (peptidoglycan-based cell wall) | Structural scaffold resisting turgor; PG pore size inversely correlates with Rod complex activity (ago2023relationshipbetweenthe pages 14-16, ago2023relationshipbetweenthe media c5a06158) |
| **Lipid II** | Lipid-linked PG precursor | CHEBI:64722 (undecaprenyl diphospho-N-acetylmuramoyl-(N-acetylglucosamine)-L-alanyl-gamma-D-glutamyl-meso-2,6-diaminopimeloyl-D-alanyl-D-alanine) | Substrate for RodA polymerization | Extracellular precursor flipped across inner membrane; polymerized by RodA (indirect relevance to width) |
| **Lipopolysaccharide (LPS)** | Outer leaflet lipid of Gram-negative outer membrane | CHEBI:25017 (lipopolysaccharide) | Increasing LPS concentration stiffens outer membrane, enabling proper MreB orientation in *mreC* mutants (fivenson2023arolefor pages 3-5, fivenson2023arolefor pages 2-3, fivenson2023arolefor pages 7-8) |
| **O-antigen** | Polysaccharide extension of LPS core | Label-only | Restoring O-antigen increases OM stiffness, rescuing rod shape defects (fivenson2023arolefor pages 7-8) |
| **ATP/GTP** | Nucleotides | CHEBI:15422 (ATP), CHEBI:15996 (GTP) | Required for MreB polymerization on lipid surfaces; hydrolysis sustains dynamic filament turnover (mao2023ontherole pages 2-3, mao2023ontherole pages 14-15) |

### 2.3 Environmental Factors and Experimental Factors

| Factor | Effect | Evidence |
|--------|--------|----------|
| **Acidic pH (pH 4.6)** | Switches expression from PBP2/PBP3 to PBP2^SAL/PBP3^SAL elongasome; alters cell length and width | *Salmonella* Typhimurium acidic intracellular niche; measured in PCN medium pH 4.6 vs. pH 7.4 (castanheira2023evidenceoftwo pages 7-8, castanheira2023evidenceoftwo pages 2-3) |
| **Osmotic stress (NaCl ~1.1 Osm, sucrose ~1.0 Osm)** | Cells lacking MreB rotation (MreB^S14A ΔrodZ) lose rod shape under elevated osmolarity | *E. coli* grown in LB + osmotica (morgenstein2015rodzlinksmreb pages 5-6) |
| **Membrane fluidity** | Low fluidity impairs MreB localization; high fluidity associated with functional elongasome activity | Indirect relevance: fatty acid desaturation modulates membrane fluidity; not directly width-specific but affects Rod complex function |

### 2.4 Organelles, Cellular Localizations, and Biological Processes

| Entity | Description | Suggested Grounding | Notes |
|--------|-------------|---------------------|-------|
| **Inner (cytoplasmic) membrane** | Lipid bilayer housing MreB filaments and Rod complex | GO:0016020 (membrane), GO:0005886 (plasma membrane) | MreB binds via N-terminal amphipathic helix or hydrophobic loop (mao2023ontherole pages 2-3) |
| **Periplasmic space** | Compartment between inner and outer membranes in Gram-negatives | GO:0030288 (outer membrane-bounded periplasmic space) | Site of PG synthesis and crosslinking by PBP2 (shlosman2023allostericactivationof pages 2-3) |
| **Outer membrane (OM)** | Second lipid bilayer unique to Gram-negatives | GO:0009279 (cell outer membrane) | Provides mechanical stability; stiffness modulates MreB-directed PG synthesis (fivenson2023arolefor pages 3-5, fivenson2023arolefor pages 7-8) |

Showing the first 60 of 285 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.