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Characterisation of Pseudomonas rhamnolipids
N B Rendell1, G W Taylor, M Somerville
1Department of Clinical Pharmacology, Royal Postgraduate Medical School, London, U.K.
Abstract:
The Gram negative organism, Pseudomonas aeruginosa, is often found in the lungs of patients with cystic fibrosis and other forms of severe bronchiectasis, where it secretes a number of extracellular toxins including the mono- and dirhamnolipids. The principal monorhamnolipid from P. aeruginosa has previously been identified as rhamnosyl-3-hydroxydecanoyl-3-hydroxydecanoate (Rh-C10.C10). A number of related mono- and dirhamnolipids have been purified from cultures of a clinical isolate of P. aeruginosa and identified by fast atom bombardment and electron impact mass spectrometry: these contain the 3-hydroxyoctanoyl-3-hydroxydecanoate (C8.C10) and 3-hydroxydecanoyl-3-hydroxydodecanoate (C10.C12) homologues. Structural isomers were also present where the order of the lipid linkage was transposed (Rh-C10.C8 and Rh-C12.C10). Unsaturated mono- and dirhamnolipids containing the 3-hydroxydecanoyl-3-hydroxydodec-5-enoate (C10.C12:1) lipid were also present.
Insights
Pseudomonas aeruginosa secretes various rhamnolipids, including novel mono- and dirhamnolipids with different fatty acid chain lengths and structures. These findings expand our understanding of P. aeruginosa virulence factors in lung infections.
Area of Science:
- Microbiology
- Biochemistry
- Organic Chemistry
Background:
- Pseudomonas aeruginosa is a Gram-negative bacterium frequently found in the respiratory tracts of patients with cystic fibrosis and bronchiectasis.
- This opportunistic pathogen produces extracellular toxins, including mono- and dirhamnolipids, which contribute to its pathogenicity.
Purpose of the Study:
- To identify and characterize novel mono- and dirhamnolipids secreted by a clinical isolate of Pseudomonas aeruginosa.
- To elucidate the structural diversity of these rhamnolipids, including homologues and isomers.
Main Methods:
- Purification of extracellular rhamnolipids from P. aeruginosa cultures.
- Structural identification using fast atom bombardment mass spectrometry (FAB-MS) and electron impact mass spectrometry (EI-MS).
Main Results:
- The principal monorhamnolipid, rhamnosyl-3-hydroxydecanoyl-3-hydroxydecanoate (Rh-C10.C10), was confirmed.
- Novel homologues containing 3-hydroxyoctanoyl-3-hydroxydecanoate (C8.C10) and 3-hydroxydecanoyl-3-hydroxydodecanoate (C10.C12) were identified.
- Structural isomers, such as Rh-C10.C8 and Rh-C12.C10, and unsaturated variants like C10.C12:1, were also characterized.
Conclusions:
- The study identified a broader range of mono- and dirhamnolipids produced by P. aeruginosa than previously known.
- The structural diversity includes variations in fatty acid chain length, linkage order, and unsaturation.
- These findings contribute to a deeper understanding of P. aeruginosa's metabolic capabilities and potential virulence factors.