Flexirubin
A yellow-orange pigment found in certain bacteria
No single value: Flexirubin is a material, and its colour varies. The background shows its family, orange.
Flexirubin is a pigment that gives some bacteria colonies a strong yellow-orange hue. It is found in several genera, including Flexibacter and Flavobacterium, and its presence can be tested by a colour change with potassium hydroxide.
- Gives bacteria a strong yellow-orange colour
- Found in Flexibacter, Flavobacterium, and related genera
- Turns from gold to red-brown with potassium hydroxide
- Can be extracted with acetone for analysis
What colour is Flexirubin?
Flexirubin is a pigment that appears as a vivid yellow-orange in certain bacteria. When colonies contain both flexirubin and carotenoids, the colour is especially strong. This pigment is not found in plants or animals, but is specific to some bacterial groups.
Where does Flexirubin come from?
The pigment was first discovered in Flexibacter elegans. Its name comes from the bacteria in which it was first found. The structure of flexirubin is based on a polycarboxylic chromophore joined to a phenol by an ester bond, with an alkyl side-chain.
How is Flexirubin made?
Flexirubin is naturally produced by bacteria such as Flexibacter and Flavobacterium. In the laboratory, it can be extracted from bacterial cultures using acetone and then separated by chromatography. Chemists have also been able to make it in the lab through chemical synthesis.
Where Flexirubin is used
Flexirubin is not widely used outside microbiology, but it is important for identifying certain bacteria. Scientists use its colour and chemical reactions to test for its presence in bacterial samples.
Orange around the world
What the orange family means from country to country.
The lowest band of the flag is orange, often called apricot, after the national fruit. The constitution says it stands for the creative talent and hard work of the people.
Politics and protestNature and renewalPrideSource: Flag of ArmeniaThe flag is split corner to corner. The orange half stands for the Buddhist tradition, and the white dragon across the middle for purity.
Sacred and holySource: Flag of BhutanOn 30 September people wear orange shirts to remember the children sent to residential schools. Phyllis Webstad's new orange shirt was taken from her on her first day at one.
Mourning and deathPolitics and protestGriefSource: National Day for Truth and ReconciliationOrange is also the colour of the New Democratic Party. Its sweep of Quebec seats in the 2011 election was called the Orange Wave.
Politics and protestSource: New Democratic PartyThe flag shows the island in copper orange on white. The colour recalls copper, which was mined here in ancient times and may have taken its name from Cyprus.
Politics and protestNature and renewalSource: Flag of CyprusThe orange stripe of the flag stands for Protestants, the followers of William of Orange. In Northern Ireland the Orange Order still marches each 12 July in orange sashes.
Politics and protestSource: Orange OrderShades and relatives of Flexirubin
Colonies with both flexirubin and carotenoids show a deeper yellow-orange. The pigment can be confused with other yellow or orange bacterial pigments, but its reaction with potassium hydroxide helps distinguish it.
Questions people ask about Flexirubin
What colour is flexirubin?
Flexirubin is a pigment that appears yellow-orange in bacterial colonies.
Where does the name flexirubin come from?
The name comes from the bacterium Flexibacter elegans, where it was first found.
How do scientists test for flexirubin?
They add potassium hydroxide to a culture; if flexirubin is present, the colour changes from gold to red-brown.
What is flexirubin made from?
It is a natural pigment produced by certain bacteria, based on a polycarboxylic chromophore joined to a phenol.
Good reading and sources
The facts on this page come from the Wikipedia article "Flexirubin", written by its contributors and used under the CC BY-SA 4.0 licence, and from its Wikidata record (CC0). Rang rewrote the text in its own words, with AI assistance, and compares every page with the article to make sure no passage is copied. It may be reused under the same CC BY-SA 4.0 licence with a link back.
It may contain mistakes. The swatch is an approximation: named colours are not fixed standards, and every screen shows them a little differently. If something is wrong, tell us. Last refreshed 2026-10-03.
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