Characterization of rhamnolipids produced by a Pseudomonas aeruginosa mutant strain grown on waste oils

Abstract

Pseudomonas aeruginosa EBN-8 mutant rhamnolipids produced on waste oils were investigated using normal-phase thin layer chromatography and fast atom bombardment mass spectrometry. Negative ion mode mass spectra yielded [M – H]⁻ ions and their fragment ions, which gave some indications on the sequence of rhamnolipid biosynthesis. Five rhamnolipid homologs [viz. RC₁₀C₁₀ (m/z 503), RC₁₂C₁₀ or RC₁₀C₁₂ (531), RRC₁₀C₈ or RRC₈C₁₀ (621), RRC₁₀C₁₀ (649) and RRC₁₂C₁₀ or RRC₁₀C₁₂ (677)] were detected in four rhamnolipid combinations under the different carbon sources. The prevalence of rhamnolipids was confirmed by Fourier transform infrared and one-dimensional proton nuclear magnetic resonance. We also observed some correlations between the tensioactive characteristics and structural chemistry of the rhamnolipid surfactants.

Keywords:

• Biosurfactant
• mass spectrometry
• NMR
• Pseudomonas aeruginosa
• rhamnolipid

Acknowledgments

The authors acknowledge the Director, International Center for Chemical and Biological Sciences, University of Karachi for the mass spectrometry and ¹H NMR facilities and the Higher Education Commission, Islamabad for the research funds.