Dirhamnolipids

Dirhamnolipids are a class of glycolipid biosurfactants composed of two rhamnose sugar units linked to lipid tails. They belong to the broader family of rhamnolipids produced by certain bacteria, most notably Pseudomonas aeruginosa, and are valued for their surface-active properties. A well-known dirhamnolipid congener is Rha-Rha-C10-C10, describing two rhamnose molecules attached to β-hydroxy fatty acid chains of around 10 carbons.

Biosynthesis of dirhamnolipids occurs through a coordinated enzyme system encoded by the rhl gene cluster, including rhlA, rhlB, and rhlC. RhlA generates the lipid-derived hydroxyalkanoate precursor, RhlB transfers the first rhamnose to form a mono-rhamnolipid, and RhlC adds a second rhamnose to yield the dirhamnolipid. The sugar donor is typically dTDP-L-rhamnose. Production is regulated by quorum sensing networks in P. aeruginosa, with expression influenced by cell density and environmental conditions. Dirhamnolipids exhibit structural diversity, with variations in the lipid tail lengths and saturation, leading to multiple congeners.

Properties and applications are dominated by their amphiphilic nature, enabling reduction of surface and interfacial tensions and emulsification of hydrophobic liquids. They are studied for use in bioremediation, soil and oil-water separation, and as environmentally friendly surfactants in cleaning, cosmetics, and industrial formulations. Limitations include the association of rhamnolipid production with pathogenic bacteria and the challenge of producing sufficient quantities cost-effectively. Research efforts focus on non-pathogenic producers, genetic optimization, and process engineering to enable scalable, safe production of dirhamnolipids.