14-12-10-8-6-2)44-32-30(28(39)26(37)20(4)42-32)45-31-29(40)27(38)25(36) 19(3)41-31/h19-22,25-32,36-40H,5-18H2,1-4H3,(H,33,34)/t19-,20-,21?,22?, Rhamnolipids are a class of glycolipid produced by Pseudomonas aeruginosa, amongst other organisms, frequently cited as bacterial surfactants.

[6] Rhamnolipids are also heterogeneous in the length and degree of branching of the HAA moiety,[1] which varies with the growth media used and the environmental conditions.

This fold is a common structural motif in fatty acid synthetic proteins and RhlA shows homology to transacylases.

It has been shown using enzyme assays that the substrate for RhlA is hydroxyacyl-ACP rather than hydroxyacyl-CoA suggesting that it catalyses the formation of HAAs directly from the type II fatty acid synthase pathway (FASII).

[11] The hydroxyacyl-ACP substrate of RhlA is the product of FabG, a protein which encodes the NADPH-dependent β-keto-acyl-ACP reductase required for fatty acid synthesis.

The rhamnose moiety for mono- and di-rhamnolipids is derived from AlgC activity and the RmlABCD pathway, encoded on the rmlBCAD operon.

As mentioned previously, Pseudomonas aeruginosa has the ability to metabolise a variety of substrates including n-alkanes, hexadecane and oils.

[15][16] It has also been shown that production of rhamnolipids promotes uptake of hexadecane by overcoming the inhibitory effect of the hydrophilic interactions caused by LPS.

[17] Production of rhamnolipids is observed on hydrophobic substrates but equally high yields are achievable on other carbon sources such as sugars.

[18] Therefore, although Rhamnolipids may play a part in interaction of Pseudomonas aeruginosa with hydrophobic carbon sources, they are likely to have additional functions.

[22] The anti-microbial action of rhamnolipids may provide a fitness advantage for Pseudomonas aeruginosa by excluding other microorganisms from the colonised niche.

[3] As mentioned previously, Pseudomonas aeruginosa produces a host of virulence factors in concert, under the control of the quorum sensing system.

Rhamnolipids are reported to promote motility, thereby inhibiting attachment by preventing cells from adhering tightly to the substratum.

[32] New evidence suggests that rhamnolipids are necessary to allow Pseudomonas aeruginosa cells to overcome attachment mediated by type IV pili.

[38] Rhamnolipids and HAAs are also implicated in twitching motility, similarly the surfactant is thought to lower the surface tension allowing cells to move across the substratum.

[41] Surfactants are in demand for a wide range of industrial applications as they increase solubility, foaming capacity and lower surface tensions.