Production of a novel mannosylerythritol lipid containing a hydroxy fatty acid from castor oil by Pseudozyma tsukubaensis.

Mannosylerythritol lipids (MELs) are glycolipid biosurfactants produced by various yeasts belonging to the genus Pseudozyma, which exhibit excellent surface activities as well as versatile biochemical activities. A study on P. tsukubaensis NBRC1940 as a mono-acetylated MEL (MEL-B) producer revealed that the yeast accumulated a novel glycolipid from castor oil at a yield of 22 g/L. Its main chemical structure was identified as 1-O-β-(2'-O-alka(e)noyl-3'-O-hydroxyalka(e)noyl-6'-O-acetyl-D-mannopyranosyl)-D-erythritol designated as "new MEL-B." The new MEL-B, comprising a hydroxy fatty acid had a reduced surface tension of 28.5 mN/m at a critical micelle concentration (CMC) of 2.2×10⁻⁵ M in water. The observed CMC was 5-fold higher than that of conventional MEL-B. When conventional MEL-B was dispersed in water, it self-assembled to form the lamellar (L(α)) phase at a wide range of concentrations. In contrast, new MEL-B formed spherical oily droplets similar to the sponge (L₃) phase, which is observed in aqueous solutions of di-acetylated MEL (MEL-A). The data suggest that the newly identified MEL-B is likely to have a different structure and interfacial properties compared to the conventional MELs, and could facilitate an increase in the application of glycolipid biosurfactants.