red pigmented

Deep research

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

# Curation report: microbial trait **red pigmented**

## 1. Executive scope

- **Trait:** red pigmented
- **Identifier:** **METPO:1003028**
- **Category / kind / status:** MORPHOLOGY / CLASS / REVIEWED
- **Parent:** METPO:1003021
- **Synonym:** `Pigment_red`

### Recommended operational definition

A positive instance is a microbial colony, biomass, or cell population that appears red because the organism produces and accumulates a red pigment under the recorded culture or assay conditions. The trait is an **observable morphology**, not a single conserved biochemical pathway. In *Serratia marcescens*, the best-supported mechanism is biosynthesis of the red linear tripyrrole prodigiosin by the 14-gene `pigABCDEFGHIJKLMN` operon. Other organisms can appear red through chemically unrelated carotenoids, including lycopene, astaxanthin, torularhodin, or deinoxanthin-like compounds. A 2024 primary study describes *S. marcescens* ATCC 274 as producing a “vibrant red pigment called prodigiosin.” (esteves2024serratiamarcescensatcc pages 1-2)

### Boundary cases

1. **Do not equate the phenotype with prodigiosin.** Prodigiosin is one sufficient molecular cause, not the definition of the trait.
2. **Color is condition-dependent.** Purified prodigiosin from *S. marcescens* OK482790 was reported as red at neutral/acidic pH, pink at pH 2, and orange at pH 9, with an absorption maximum of approximately 533–540 nm. Thus pH, medium, illumination, growth phase, and scoring method should be recorded as assay context. (hamada2024characterizationofserratia pages 8-9)
3. **Exclude red fluorescence without red visible pigmentation**, staining by an exogenous dye, red medium caused by a secreted product when colonies/cells themselves were not scored, blood agar hemolysis, and host-derived coloration.
4. **Orange, pink, yellow, or brown isolates are not automatically positive.** Curate them only if the source explicitly calls the colony/cells red under specified conditions.
5. **Production capacity versus observed morphology:** a biosynthetic gene cluster predicts capacity, whereas METPO:1003028 should normally require observed red appearance or chemically confirmed pigment production linked to appearance.

## 2. Current mechanistic model

The strongest TraitMech-ready model is a taxon-qualified *Serratia* prodigiosin graph:

1. The `pigA–pigN` operon encodes two precursor branches.
2. The MAP branch produces 2-methyl-3-*n*-amylpyrrole; the MBC branch produces 4-methoxy-2,2′-bipyrrole-5-carbaldehyde.
3. PigC performs terminal condensation of the two branch products to form prodigiosin.
4. Accumulated prodigiosin generates the visible red phenotype.
5. Transcription is modulated by direct and indirect regulators and by environmental inputs, including temperature, phosphate status, quorum-sensing context, and phage infection. The pathway assignment reported by Sun et al. is `pigD/pigE/pigB` for MAP and `pigA` plus `pigF–pigN` for MBC. (sun2020improvedprodigiosinproduction pages 1-2)

| subject | predicate | object | taxon/strain | evidence type | confidence | DOI |
|---|---|---|---|---|---|---|
| pigABCDEFGHIJKLMN operon | enables biosynthesis of | prodigiosin | *Serratia marcescens* ATCC 274; JNB5-1 | operon/genetic evidence, transcriptional response (esteves2024serratiamarcescensatcc pages 1-2, pan2021regulatorrcsbcontrols pages 7-10) | High | 10.1038/s41598-024-68747-3; 10.1128/AEM.02052-20 |
| MAP precursor branch + MBC precursor branch | are condensed by | PigC to form prodigiosin | *Serratia* spp. / prodigiosin pathway literature | pathway/mechanistic review summarized from primary studies (esteves2024serratiamarcescensatcc pages 11-12, sun2020improvedprodigiosinproduction pages 1-2) | High | 10.1038/nrmicro1531; 10.3389/fbioe.2020.00344 |
| prodigiosin | causes | red pigmented phenotype | *Serratia marcescens* ATCC 274; OK482790 | phenotype-chemistry association, pigment characterization (esteves2024serratiamarcescensatcc pages 1-2, hamada2024characterizationofserratia pages 8-9) | High | 10.1038/s41598-024-68747-3; 10.1186/s12866-024-03634-5 |
| Chi phage infection | increases transcription of | pig operon | *Serratia marcescens* ATCC 274 | primary infection/reporter assay (esteves2024serratiamarcescensatcc pages 1-2) | High | 10.1038/s41598-024-68747-3 |
| Chi phage infection | increases production of | prodigiosin | *Serratia marcescens* ATCC 274 | primary infection/phenotype assay (esteves2024serratiamarcescensatcc pages 1-2) | High | 10.1038/s41598-024-68747-3 |
| CpxR | directly represses transcription of | pig gene cluster promoter | *Serratia marcescens* JNB5-1 | primary EMSA + mutant analysis (sun2020improvedprodigiosinproduction pages 1-2) | High | 10.3389/fbioe.2020.00344 |
| MetR | directly represses transcription of | pigP | *Serratia marcescens* | primary EMSA + RT-qPCR/transcriptomics (pan2020lysrtypetranscriptionalregulator pages 1-2) | High | 10.1128/AEM.02241-19 |
| PigP | positively regulates | pig operon | *Serratia marcescens* | regulator linkage from direct MetR→pigP repression and pigP as positive regulator (pan2020lysrtypetranscriptionalregulator pages 1-2) | High | 10.1128/AEM.02241-19 |
| RcsB | binds promoter of and negatively regulates | flhDC | *Serratia marcescens* JNB5-1 | primary EMSA + expression analysis (pan2021regulatorrcsbcontrols pages 10-12, pan2021regulatorrcsbcontrols pages 46-48) | High | 10.1128/AEM.02052-20 |
| FlhDC | activates biosynthesis of | prodigiosin | *Serratia marcescens* JNB5-1 | primary regulatory genetics downstream of RcsB (pan2021regulatorrcsbcontrols pages 10-12, pan2021regulatorrcsbcontrols pages 1-3) | High | 10.1128/AEM.02052-20 |


*Table: This table summarizes the strongest, most curation-ready causal edges for the red pigmented trait METPO:1003028, emphasizing direct genetic and regulatory evidence in Serratia prodigiosin systems. It is useful as a compact starting point for building a TraitMech YAML graph while preserving taxon specificity and confidence.*

## 3. Candidate nodes grouped by type

### A. Trait and observable-state nodes

| Candidate node | Suggested grounding | Curation note |
|---|---|---|
| red pigmented | **METPO:1003028** | Terminal phenotype node; quote the CURIE verbatim. |
| pigmentation phenotype | METPO:1003021 | Supplied parent trait. |
| red colony/cell appearance | Label only | Assay-observed state; keep distinct from pigment concentration. |
| pigment accumulation | GO biological-process candidate; verify exact term before use | Proximal process linking chemistry to visible phenotype. |

### B. Pathways and metabolic modules

Showing the first 60 of 261 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.