THE FLEXIRUBIN-TYPE PIGMENTS, CHEMOSYSTEMATICALLY USEFUL COMPOUNDS

Abstract

The flexirubin-type pigments are compounds of a novel chemical structure: A polyenoic acid chromophore with a para-hydroxy phenyl ring (ring A) in the end position is esterified with a di-alkylated resorcinol (ring B). The basic structure may be modified by a) a variation of the chain length of the chromophore between 6 and 8 conjugated double bonds; b) a methylation in the meta-position in ring A; c) a chlorination in the meta-position in ring A; and d) broad variations of the hydrocarbon chains in ring B with respect to the chain length and linearity. All strains, which contain flexirubin-type pigments, also produce chlorinated counterparts of most of the structural variants. The distribution of flexirubin-type pigments among yellow bacteria makes them very useful chemosystematic markers. They are found in most strains of Flexibacter and Cytophaga-like bacteria isolated from soil and freshwater, in Sporocytophaga, and in many flavobacteria of the low GC-group. They seem to be absent in gram-positive bacteria, in flagellated bacteria, and in most Cytophaga-like bacteria isolated from marine environments. Many bacteria, which produce flexirubintype pigments, contain complex mixtures of up to 25 different structural variants, but nevertheless it seems that each taxonomic group synthesizes its own specific modification of the pigment. In contrast to carotenoids, also present in many of the above-mentioned organisms, flexirubin-type pigments are located in the outer membrane of the gram-negative cell wall. The biological function of the new pigments is still obscure: Unpigmented mutants can be obtained, and grow well under laboratory conditions.