Use of liquid chromatography-mass spectroscopy for studying the composition and properties of rhamnolipids produced by different strains of Pseudomonas aeruginosa

Abstract

Biosurfactants are produced as a mixture of different homologs. The application of liquid chromatography-electrospray mass spectrometry in negative mode for the analysis of rhamnolipid mixtures AT10 and 47T2 has been studied. Working at low (up to −35V) extraction voltages, the [M-H]− for each compound was obtained. Increasing this potential to −75V 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 RLAT10 (Rha-Rha-C10-C10; Rha-Rha-C10-C12:1; Rha-Rha-C10-C12; Rha-C10-C12:1; Rha-C10-C10; RhaC10-C12:1; Rha-C10-C12; Rha-C8:1; Rha-C12:2) and RL47T2 (Rha-Rha-C8-C10; Rha-Rha-C8-C12:1; Rha-Rha-C10-C10; Rha-Rha-C10-C12:1; Rha-Rha-C10-C12; Rha-Rha-C12-C10; Rha-Rha-C12:1-C12; Rha-Rha-C10-C14:1; Rha-C8-C10; Rha-C10-C8; Rha-C10-C10; Rha-C10-C12:1; Rha-C10-C12; Rha-C12-C10, where Rha=rhamnose moiety) are compared. The surface tensions found were 26.8 and 32.8 mN/m for RLAT10 and RL47T2, respectively. These two products differ in their antimicrobial properties, as based on their minimal inhibition concentrations (MIC). RLAT10 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 RL47T2 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).