Lipase-catalyzed acylation of microbial mannosylerythritol lipids (biosurfactants) and their characterization

• In vitro enzymatic modifications of mannosylerythritol lipids.
• Lipase-catalyzed acylations of MEL-A and MEL-B.
• Acyl donors: uncommon fatty acids from other biosurfactants.
• New glycoconjugates lowered the surface tension of water to 27–38 mN m−1.

Culturing Pseudozyma aphidis on glucose as main carbon source and soybean oil as co-substrate the mannosylerythritol lipids MEL-A and MEL-B were produced. Based on their excellent surface/interfacial active behavior they possess a high potential among all known biosurfactants. The components of a microbial MEL mixture were purified by medium pressure liquid chromatography (MPLC) and were used as substrates for in vitro enzymatic modifications. Lipase-catalyzed acylations of MEL-A and MEL-B with uncommon fatty acids from other microbial glycolipids—3-hydroxydecanoic acid from rhamnolipids and 17-hydroxyoctadecanoic acid from classical sophorolipids—yielded functionalized products at the C-1 position of the erythritol. The novel products were purified by MPLC and their structures elucidated by 1H and 13C nuclear magnetic resonance spectroscopy and mass spectrometry. In physicochemical characterization experiments two of the three new glycoconjugates lowered the surface tension of water from 72 mN m−1 to 27–38 mN m−1. Moreover the novel compounds inhibited the growth of gram-positive bacteria and showed a potential for anti-tumor-promoting activity.

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