Flexirubin is the main pigment in the bacteria genera Flexibacter, Flavobacterium, Chryseobacterium, and Cytophaga.Reichenbach, H., W. Kohl, et al. (1980). FLEXIRUBIN-TYPE PIGMENTS IN FLAVOBACTERIUM. Archives of Microbiology 126(3): 291–293. It was isolated for the first time from Flexibacter elegans. Flexirubin is found in these genera, as well as those that produce carotenoids. The pigment mixture of flexirubin and carotenoids imparts colonies with an intense yellow-orange color.Hans Achenbach, W. Kohl, et al. (1976). INVESTIGATIONS ON METABOLITES OF MICROORGANISMS .11. FLEXIRUBIN, A NOVEL PIGMENT FROM FLEXIBACTER-ELEGANS. Chemische Berichte-Recueil 109(7): 2490–2502. Structurally, this bacteria pigment is based on a polycarboxylic-chromophore that is linked with a phenol by an ester, resulting in an alkyl side-chain.Achenbach, H., W. Kohl, et al. (1974). STRUCTURE OF FLEXIRUBIN. Tetrahedron Letters(30): 2555–2556. The first total synthesis of flexirubin was reported in 1977.Achenbach, H. and J. Witzke (1977). TOTAL SYNTHESIS OF FLEXIRUBIN DIMETHYL ETHER. Angewandte Chemie-International Edition in English 16(3): 191–192.
To test for the presence of flexirubin, a cultural strain with a 20% potassium hydroxide solution is created. A color change from gold to red-brown indicates the presence of flexirubin. Alternatively, the pigment can also be extracted with acetone and chromatographic methods can be used to ascertain its presence.
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