Monorhamnolipids

Monorhamnolipids are a class of biosurfactants in the glycolipid family produced by certain bacteria, most notably Pseudomonas species. They consist of a lipid portion derived from beta-hydroxy fatty acids linked to a single rhamnose sugar. This distinguishes them from dirhamnolipids, which contain two rhamnose units. Monorhamnolipids commonly feature two fatty acid chains, often in the C10–C12 range, with variations in chain length and saturation.

Biosynthesis of monorhamnolipids involves the rhl gene cluster. RhlA and RhlB participate in forming the lipid moieties and attaching the rhamnose donor to produce mono-rhamnolipids, while RhlC adds a second rhamnose to yield dirhamnolipids. The balance between mono- and di-rhamnolipid production can depend on the strain and culture conditions.

Physicochemical properties of monorhamnolipids include surface-active behavior, the ability to reduce surface tension, and emulsification of hydrophobic compounds. They have practical utility because of biodegradability and relatively low toxicity compared with some synthetic surfactants, with performance dependent on chain length, degree of rhamnosylation, pH, and salinity.

Applications span environmental and industrial contexts, including bioremediation and cleanup of oil hydrocarbons, enhanced oil recovery, and use as emulsifiers in cosmetics and cleaning products. Production is typically via microbial fermentation, with ongoing work to optimize yields and to employ non-pathogenic production hosts for safety and regulatory reasons. Analytical methods such as LC-MS and surface tension measurements are used to characterize monorhamnolipids and assess their surfactant properties.