Title: Structural characterization of novel extracellular liamocins (mannitol oils) produced by Aureobasidium pullulans strain NRRL 50380 Authors
Submitted to: Carbohydrate Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 21, 2013
Publication Date: April 5, 2013
Citation: Price, N.P., Manitchotpisit, P., Vermillion, K., Bowman, M.J., Leathers, T.D. 2013. Structural characterization of novel extracellular liamocins (mannitol oils) produced by Aureobasidium pullulans strain NRRL 50380. Carbohydrate Research. 370(4):24-32. Interpretive Summary: Biosurfactants are biologically produced chemicals that have potential to replace petroleum-based detergents. We have discovered a new type of biosurfactant from a common fungus that was previously shown to produce heavier-than-water oils. Using a combination of chemical and spectroscopic techniques we have solved the chemical structure of four new biosurfactants. We also found four smaller components, called exophilins, that are known to have anti-microbial properties. Because of the relatively high yield and surfactant-like properties of these new materials we anticipate their potential value as replacements for petroleum-based detergents and emulsifiers.
Technical Abstract: Aureobasidium pullulans is a common, ubiquitous fungus, which is used industrially to produce the polysaccharide pullulan. We have previously shown that A. pullulans produces various heavier-than-water oils, first named here as liamocins, that accumulate in fermentations. Here we report the structural characterization of four liamocins produced by A. pullulans strain NRRL 50380, A1, A2, B1, and B2, using a combination of MALDI-TOF/MS, quadrupole-TOF/MS, isotopic labeling, NMR, GC/MS, and classical carbohydrate analysis. The data showed that the liamocins are composed of a single mannitol headgroup partially O-acylated with three (for liamocin A1 and A2) or four (for liamocin B1 and B2) 3, 5-dihydroxydecanoic ester groups. Liamocins A1 and B1 are non-acetylated, whereas A2 and B2 each contain a single 3’-O-acetyl group. Each of these compounds is characterized by pseudomolecular [M + Na]+ ions in the MALDI-TOF/MS spectra at m/z 763.22, 949.35, 805.22, and 991.37, respectively. The 186 Da mass difference between and A-type and B-type liamocins corresponds to one O-linked 3, 5-dihydroxydecanoate group. HMBC NMR showed that one 3, 5-dihydroxydecanoate carbonyl group is ester linked to a primary hydroxyl on the mannitol. Other long range 13C-1H couplings across 1, 5-ester bridges showed that the 3, 5-dihydroxydecanoate groups form 1 - 5-linked polyester chains, similar in structure to the antibiotic substance exophilin A. Moreover, the MS analysis identified several non-conjugated poly-3, 5-dihydroxydecanoate esters as minor components that are tentatively assigned as exophilins A1, A2, B1, and B2. The liamocins, and three of the exophilins, are new, previously unreported structures.