Intracellular location of flexirubins in Flexibacter elegans (Cytophagales)

The inner and outer membranes of 2 strains of Gram-negative Flexibacter elegans, Fx e1 and Fx 3/4, could be separated on sucrose density gradients after the cells had been converted into spheroplasts, and the spheroplasts had been lysed in presence of EDTA and the detergent Brij 58. The light fraction (rho = 1.14 g . cm-3) contained the components of the respiratory chain in high concentrations, but only low amounts of the lipopolysaccharide component, 2-keto-3-deoxyoctonic acid, and was thus mainly material from the inner membrane. The heavy fraction (rho = 1.175 g . cm-3) contained only traces of respiratory chain enzymes, but the majority of the 2-keto-3-deoxyoctonic acid, and was thus mainly material from the outer membrane. The flexirubin pigments were found almost quantitatively in the latter fraction. Strain Fx 3/4 produced carotenoids in addition to flexirubins; in this case the flexirubins were located in the outer, and the carotenoids in the inner membrane.