rhamnolipid

Rhamnolipids have two moieties: Rhamnose (also known as glycon part) and lipid (also known as aglycon part). Rhamnose moiety is hydrophilic in nature comprising of mono or di (L)-rhamnose molecules which are linked together through α-1,2-glycosidic linkage. The lipid moiety is hydrophobic in nature and comprises of one or more saturated/unsaturated β-hydroxy fatty acids chains of C8−C24 lengths, linked together with an ester bond. Both moieties are linked via glycosidic linkage. The structural properties of microbial rhamnolipids depend on environmental and growth conditions. They are generally obtained as complex mixtures of congeners: mono-rhamnolipids and di-rhamnolipids, differing in the number of rhamnose groups present; within each of these two classes, congeners differ in terms of chain length, degree of branching, and unsaturation of the fatty acid chains. For example, rhamnolipids produced by P. aeruginosa are mixtures of about 30 different molecules; by considering all the possible microbial origins, up to 60 rhamnolipid congeners and homologs have been identified.

Rhamnolipid is known as a biosurfactant and is secreted from the bacterium - pseudomonas aeruginosa. Surfactants are soaps made from petroleum. Biosurfactants are soaps made without petroleum and are ubiquitous. They are found indoors and outdoors. They can be found on tabletops, clothes, trees and animals.

biosurfactant

Rhamnolipid (with rhamnolipid being both singular and plural i.e. fish) have widespread application and their utility across several diverse industries (pharmaceutical, cosmetics, food, environmental clean-up, agriculture, water treatment, oil and heavy petroleum recovery (enhanced oil recovery) and soil washing) is being recognized world wide as a non-toxic, biodegradable environmentally safe application.

Different carbon sources can affect the supply of basic precursors for the biosynthesis of rhamnolipids, and because of this reason, different PA strains produce variants of rhamnolipids. A complex genetic network is required for RLs production, including the rhl genes (A, B, and C), quorum sensing, and three main steps which give rise to dTDP-l-rhamnose and variants of 3-(3-hydroxyalkanoyloxy) alkanoic acid (primarily β-Hydroxydecanoyl-β-Hydroxydecanoate; HAA). The three steps are: (a) RhlA enzyme transfers the β-hydroxydecanoyl present on the acyl carrier protein (ACP) to the coenzyme A (CoA) and forms β-hydroxydecanoyl-CoA intermediate in de novo fatty acid synthesis. RhlA directs the formation of β-Hydroxydecanoyl-β-Hydroxydecanoate (HAA) (a part of rhamnolipid) from the type II fatty acid synthase pathway whereas d-glucose synthesized dTDP-1-rhamnose. (b) RhlB rhamnosyltransferase involves synthesizing mono-RL using dTDP-1-rhamnose and 3-(3-hydroxyalkanoyloxy) alkanoic acid as precursors. (c) RhlC rhamnosyltransferase directs the condensation of mono-RLs and dTDP-1-rhamnose to synthesize di-rhamnolipids. Rhamnolipids production is transcripShreya delete from heretionally regulated through quorum sensing signals. RhlI and LasI enzymes are responsible for synthesizing autoinducer molecules; autoinducer molecules, when reaching the threshold concentration, persuade the Rhl genes expression by binding to their regulatory proteins LasI and RhlR[1].

[1] Priyanka Thakur. “Rhamnolipid the Glycolipid Biosurfactant: Emerging trends and promising strategies in the field of biotechnology and biomedicine.” Microbial Cell Factories (2021): 1.