The rhamnolipids produced by Pseudomonas aeruginosa strains are often a mixture of several homologues. Up to seven (R2C10C10 + R1C10C10 + R2C10C12 + R1C10C12 + R1C12:1C10 + R1C12:2 + R1C8:2 ) have been identified in cultures of P. aeruginosa AT10 from soybean oil refinery wastes. This study deals with the production, purification, and identification of rhamnolipids in the mixture (M7), as well as their physical and chemical characterization and the evaluation of their antimicrobial properties. The surface tension decreases to 26.8 mN/m and the critical micelle concentration value to 1.2 × 102 mg/L. These molecules show excellent antifungal properties against Aspergillus niger and Gliocadium virens (16 μg/mL) and C. globosum, P. crysogenum , and A. pullulans (32 μg/mL), whereas the growth of the phytopathogenic fungi B. Cinerea and R. solani was inhibited at 18 μg/mL.

Pseudomonas aeruginosa LBI isolated from petroleum-contaminated soil produced rhamnolipids (RL(LBI)) when cultivated on soapstock as the sole carbon source. HPLC-MS analysis of the purified culture supernatant identified 6 RL homologues (%): R(2) C(10) C(10) 28.9; R(2) C(10) C(12:1) 23.0; R(1) C(10) C(10) 23.4; R(2) C(10) C(12) 11.3; R(2) C(10) C(12) 7.9; R(2) C(10) C(12) 5.5. To assess the potential antimicrobial activity of the new rhamnolipid product, RL(LBI), its physicochemical properties were studied. RL(LBI) had a surface tension of 24 mN m(-1) and an interfacial tension of 1.31 mN m(-1); the cmc was 120 mg l(-1). RL(LBI) produced stable emulsions with hydrocarbons and vegetable oils. This product showed good antimicrobial behaviour against bacteria: MIC for Bacillus subtilis, Staphylococcus aureus and Proteus vulgaris was 8 mg l(-1), for Streptococcus faecalis 4 mg l(-1), and for Pseudomonas aeruginosa 32 mg l(-1). RL(LBI) was active against phytopathogenic fungal species, MIC values of 32 mg l(-1) being found against Penicillium, Alternaria, Gliocadium virens and Chaetonium globosum. Due to its physicochemical properties and antimicrobial behaviour, RL(LBI) could be used in bioremediation treatment and in the food, cosmetic and pharmaceutical industries.

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Biosurfactants are produced as a mixture of different homologs. The application of liquid chromatographyelectrospray mass spectrometry in negative mode for the analysis of rhamnolipid mixtures AT10 and 47T2 has been studied. Working at low (up to −35 V) extraction voltages, the [M − H] − for each compound was obtained. Increasing this potential to −75 V produced an increase in the fragmentation of compounds and enabled the co-eluting isomers of rhamnolipids to be distinguished and their proportions in the sample to be calculated. In this work, the physicochemical and biological properties of two different rhamnolipid mixtures produced by two Pseudomonas strains RL AT10 , where Rha = rhamnose moiety) are compared. The surface tensions found were 26.8 and 32.8 mN/m for RL AT10 and RL 47T2 , respectively. These two products differ in their antimicrobial properties, as based on their minimal inhibition concentrations (MIC). RL AT10 was effective against the fungal species (MIC) Aspergillus niger (16 µg/mL); Gliocadium virens (16 µg/mL); Penicillium chrysogenum (32 µg/mL); Botrytis cinerea (18 µg/mL); and Rhizoctonia solani (18 µg/mL), whereas RL 47T2 was more effective against the bacteria (MIC) Enterobacter aerogenes (4 µg/mL); Serratia marcescens (8 µg/mL); Bacillus subtilis (16 µg/mL); and Staphylococcus aureus (32 µg/mL).Paper no. S1312 in JSD 6, 155-161 (April 2003).Biosurfactants are a structurally diverse group of surfaceactive molecules synthesized by microorganisms. Being amphiphilic molecules, they generally absorb at interfaces and reduce the surface tension between two liquid phases, enabling the uptake of hydrophobic substrates by the microorganism. Bioemulsifiers have very different chemical structures and are produced by a wide variety of microorganisms living in different habitats, thus providing the cell with different physiological and therefore ecological advantages. Rhamnolipids (RL), the most well-known bioemulsifiers, are produced by different strains of Pseudomonas aeruginosa, and their production process and recovery have been studied extensively. Up to four different molecules have been identified, depending on the strain and on culture conditions (1,2). RL mixtures traditionally have been analyzed by colorimetric determination of total hexoses (3) or by specific assay for rhamnose (4). The main advantage of these methods has been simplicity, and the main drawback has been that neither provides composition information.A further advance in the quantification of RL was the application of LC coupled to a diode array detector (5), enabling up to four species of molecules to be quantified separately. More recent studies have used liquid chromatography (LC) coupled with MS (LC-MS) for determining RL or their precursors (6-9). The main advantage of this method is that it provides information that enables identification of the composition of the mixture. Soft ionization in atmospheric pressure ionization techniques, e.g., electrospray (ES), produces little structural information, but a proper adjustm...