Polyol lipids, also known as liamocins, are a class of surface active glycolipids [1]. These microbiologically produced lipids (alongside others) are also referred to as biosurfactants. Compared to chemically synthesized surfactants derived from fossil fuels, biosurfactants provide a more environmentally friendly and less toxic alternative. These compounds typically consist of a hydrophilic head group made up of a sugar component and a hydrophobic tail composed of fatty acids. In case of polyol lipids, the chemical structure includes a hydrophilic head region comprised of diverse sugar alcohols, such as mannitol or arabitol, connected to a hydrophobic tail formed by three or four 3,5-dihydroxydecanoic acids (DHDA). Additionally, acetylation at the 3-OH position of the 3,5-dihydroxydecanoic acid immediately attached to the sugar alcohol is possible. Other potentially relevant biosurfactant structures have also been described in Aureobasidium pullulans, including exophilins, also known as tri- and tetradihydroxydecanoic acids (3DDA and 4DDA) [1]. Due to its rich portfolio of potential biosurfactants, research has increasingly focused on the dark, yeast-like fungus Aureobasidium pullulans.
Because of the high structural diversity of polyol lipids, chromatographic separation and high resolution mass spectrometry (HRMS) are necessary for identification. Reversed-phase liquid chromatography (RP-LC) effectively separates various classes of polyol lipids. High resolution mass spectrometry using electrospray ionization (in positive mode) and data-dependent tandem mass spectrometry (MS/MS) allow for a comprehensive detection and characterization of polyol lipids and similar substances. Post-column splitting via a t-piece enables a simultaneous detection and relative interclass quantification via a charged aerosol detector (CAD). By examining several mutant strains and different conditions during cultivation of Aureobasidium pullulans, its versatility as a producer of biosurfactants is showcased.
In this study, an efficient method for separating and identifying polyol lipids present in Aureobasidium pullulans strains was developed. Furthermore, this study provides a relative quantitative analysis of various polyol lipid classes and their distribution in different mutant strains and cultivation conditions. The results presented in this work highlight potential different parameters for optimizing the biotechnological production of biosurfactants in Aureobasidium pullulans.
[1] Tiso, T.; Welsing, G.; Lipphardt, A.; Sauer, D. F.; Chi, Z.; Blank, L. M.; Hayen, H. J Surfact Deterg. 2024, 27, 459-461.