Molecular and structural characterization of the biosurfactant produced by Pseudomonas aeruginosa DAUPE 614

Pseudomonas aeruginosa DAUPE 614 produced rhamnolipids (3.9 g L−1) when cultivated on a medium containing glycerol and ammonium nitrate. These rhamnolipids reduced the surface tension of water to 27.3 mN m−1, with a critical micelle concentration of 13.9 mg L−1. The maximum emulsification index against toluene was 86.4%. The structure of the carbohydrate moiety of the glycolipid was determined by gas chromatography–mass spectroscopy (GC–MS) analysis allied to electrospray ionization mass spectrometry and nuclear magnetic resonance (NMR) 1D, 2D 13C, 1H spectroscopy. The hydroxyl fatty acids were analyzed by GC–MS as hydroxy-acetylated fatty acid methyl ester derivatives. The positions of the fatty acids in the lipid moiety were variable, with 6 mono-rhamnolipid homologues (Rha-C10-C10; Rha-C10-C8; Rha-C8-C10; Rha-C10-C12:1; Rha-C12-C10; Rha-C10-C12) and 6 di-rhamnolipid homologues (Rha2-C10-C10; Rha2-C10-C8; Rha2-C8-C10; Rha2-C10-C12:1; Rha2-C12-C10; Rha2-C10-C12). The ratio of Rha2-C10-C10 to Rha-C10-C10 was higher than has been reported in previous studies. Our methodology allowed us to distinguish between the isomeric pairs Rha-C10-C8/Rha-C8-C10, Rha-C10-C12/Rha-C12-C10, Rha2-C10-C8/Rha2-C8-C10 and Rha2-C12-C10/Rha2-C10-C12. For each isomeric pair, the congener with the shorter chain adjacent to the sugar was always more abundant than the congener with longer chain.