Rhamnose and rhamnolipide biosynthesis by Pseudomonas aeruginosa.

Pseudomonas aeruginosa produces, when grown on a glycerol or fructose medium, a unique glycolipide composed of 2 moles each of L-rhamnose and ,%hydroxydecanoic acid. The formula of the isolated compound as determined by Jarvis and Johnson (3) is shown in Fig. 1. Various aspects of the conditions under which this rhamnolipide is produced have been investigated previously. Further, a synthetic medium for its production and a suitable assay have been developed (4). In addition to the interest concerning the whole molecule as an example of a simple crystalline glycolipide, both constituent moieties are of considerable significance in their own right. Rhamnose is the most widely occurring and best known methylpentose, yet ,no information is available about its origin in nature. The most common n-rhamnose-containing natural products are quercitrin and naringin (5), but the sugar has also been identified in certain cardiac glycosides and saponins (6), in some plant pigments (5), in bacterial polysaccharides (7) and lipopolysaccharides (8), and in plant gums and mucilages (9). Since P. aeruginosa cultures produce relatively large quantities of rhamnolipide (4), they offered a suitable system for the study of rhamnose biosynthesis. P-Hydroxydecanoic acid is one of a limited number of hydroxylated fatty acids in nature. However, evidence as to the essential role of flhydroxy fatty acids in the synthesis and breakdown of fatty acids has accumulated in recent years (10) and in this connection the lipide component of the rhamnolipide assumes importance. In the present paper, data on the incorporation of radioactivity from glycerol-c&14, glycerol-P-C14, and acetate-l-Cl4 into rhamnolipide have