yellow pigmented

Deep research

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

# Curation report: microbial “yellow pigmented”

**Target:** `METPO:1003030`
**Category:** MORPHOLOGY | **Kind:** CLASS | **Mapping:** REVIEWED
**Parent:** `METPO:1003021` | **Synonym:** *Pigment_yellow*

## 1. Scope and current interpretation

`METPO:1003030` should represent an **observed yellow appearance of microbial colonies or cells under stated assay conditions**, not merely possession of a pigment-biosynthesis gene or the ability to produce an extractable pigment. The proximate cause is accumulation of chromophores whose visible absorption produces a yellow phenotype. Carotenoids are especially important: they are lipid-soluble isoprenoids, generally absorb at 440–520 nm, and span yellow through deep-red colors depending on structure. Bacteria principally derive them through the MEP/DOXP or mevalonate precursor pathways. More than 700 carotenoid varieties have been described, emphasizing that color does not uniquely identify a compound (huang2024bacterialpigmentsas pages 3-4).

The strongest experimentally resolved examples are **β-carotene, zeaxanthin, and nostoxanthin**. In *Novosphingobium aromaticivorans*, both a zeaxanthin-accumulating `ΔcrtG` mutant and a β-carotene-accumulating `ΔcrtGΔcrtZ` mutant formed yellow colonies; the authors explicitly noted that colonies can look similar despite containing different carotenoids because their absorption spectra overlap (hall2023productionofcarotenoids pages 2-6). Thus, yellow appearance is a morphological endpoint downstream of several possible chemistries—not a synonym for “carotenoid producer.”

### Boundary cases

Include only when the cells or colonies themselves are documented as yellow:

- **Include:** yellow or deep-yellow colony/cell pigmentation supported by visual observation, colorimetry, or a linked pigment assay.
- **Do not automatically include:** an organism carrying `crt` genes without observed yellow color; genomic prediction is insufficient.
- **Distinguish from adjacent colors:** lycopene accumulation can produce red or light-pink colonies, whereas phytoene is colorless. Orange, golden, cream, tan, and pink phenotypes require explicit mapping policy rather than automatic inclusion (hall2023productionofcarotenoids pages 2-6, liu2021engineeringsphingobiumsp. pages 2-4).
- **Distinguish from medium pigmentation:** secreted yellow pigment that colors the supernatant is a pigment-production phenotype unless cell/colony color is also demonstrated.
- **Distinguish from fluorescence:** yellow fluorescence under excitation is not necessarily yellow pigmentation in visible reflected light.
- **Non-carotenoid boundary:** flexirubin-type pigments, xanthomonadins, aryl polyenes, and some melanins can appear yellow. They belong in this trait only where yellow colony/cell appearance is documented; their pathways should remain separate from the carotenoid branch.
- **Condition dependence:** temperature, pH, nutrients, light, oxygen, growth phase, and medium can alter pigment abundance. Record assay conditions rather than treating color as invariably expressed.

## 2. Recommended graph architecture

A useful graph should separate:

1. **precursor supply**—MEP/DOXP or MVA pathway → IPP/DMAPP → GGPP;
2. **carotenoid pathway**—GGPP → phytoene → lycopene → β-carotene → zeaxanthin → caloxanthin/nostoxanthin;
3. **regulation and environment**—for example, cAMP–CRP regulation and culture conditions;
4. **physical accumulation/localization**—cell-associated or membrane-associated carotenoid;
5. **assay endpoint**—yellow colony/cell appearance (`METPO:1003030`).

This avoids asserting that every upstream carotenoid step directly causes yellow color: phytoene is colorless and lycopene is generally red, while pathway blocks can change the final hue (liu2021engineeringsphingobiumsp. pages 4-5, liu2021engineeringsphingobiumsp. pages 2-4).

## 3. Candidate nodes grouped by type

### Trait and assay nodes

- Yellow pigmented — `METPO:1003030`
- Pigmentation phenotype — `METPO:1003021`
- Yellow colony appearance — label-only assay endpoint
- Yellow cell appearance — label-only assay endpoint
- Nonpigmented colony; light-pink colony; red colony; deep-yellow colony — label-only comparator states
- HPLC/UV–visible carotenoid detection; LC–MS pigment identification; visual colony-color screening — label-only experimental nodes

### Pathways and biological processes

- Carotenoid biosynthetic process — `GO:0016117`
- Isoprenoid biosynthetic process — `GO:0008299`
- MEP/DOXP pathway — label plus pathway-database mapping after curator verification
- Mevalonate pathway — label plus pathway-database mapping after curator verification
- β-carotene biosynthesis, zeaxanthin biosynthesis, nostoxanthin biosynthesis — label-only until exact pathway identifiers are verified
- Carotenoid accumulation; pigment accumulation; response to oxidative stress; photoprotection — GO grounding should be selected only after matching the precise experimental claim

### Genes, proteins, and enzymes

- `crtE` / geranylgeranyl-diphosphate synthase
- `crtB` / phytoene synthase

Showing the first 60 of 237 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.