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, A1, A2, B1, and B2, produced by A. pullulans strain NRRL 50380 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 186Da mass difference between 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 (13)C-(1)H 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.
biosurfactants, Aureobasidium pullulans, liamocins, polyol oils, MALDI-TOF/MS, exophilins
NCBI PubMed ID: 23435167Publication DOI: 10.1016/j.carres.2013.01.014Journal NLM ID: 0043535Publisher: Elsevier
Correspondence: Price NP
Institutions: Renewable Product Technology, National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, Peoria, IL, USA, Functional Food, National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, Peoria, IL, USA, Bioenergy Research Units, National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, Peoria, IL, USA, Department of Biochemistry, Rangsit University, Muangake, Lakhok, Patumthani, Thailand.
Methods: 13C NMR, 1H NMR, acid hydrolysis, MALDI-TOF MS, DOSY, HMBC, COSY, HSQC, GC/MS
Found