Modification of the mannitol biosynthetic pathway in Aureobasidium pullulans to alter the structure of the polyol lipid liamocin

Aureobasidium pullulans is an important industrial organism that is utilized for the production of numerous bioproducts, such as pullulan, β-glucan, aureobasidin, and polymalic acid. Our laboratory is also interested in production of the extracellular polyol lipids, called liamocins, produced by certain isolates of A. pullulans under nitrogen limiting conditions. Liamocins are comprised of a polyol head group that is ester-linked at one end to a 3, 5-dihydroxydecanoic acid, which is sequentially coupled to several other 3, 5-dihydroxydecanoic acid groups. Mannitol headgroups are usually the predominant structure when glucose, fructose, sucrose, or xylose is used as the carbon source, but some A. pullulans strains produce liamocins that are up to 40% arabitol-containing structures. We have shown that liamocins have biosurfactant properties and differentially inhibited mammalian cancer cell lines. Most recently, we determined that these microbial oils have potent selective antibacterial activities against certain Gram positive organisms that are important in veterinary and clinical medicine. The inhibitory properties of liamocins are partly influenced by the type of polyol head group, so we developed methods to alter the mannitol biosynthetic pathway to better control the type of liamocin produced. Deletion of the mannitol 1-phosphate dehydrogenase shifted intracellular accumulation of mannitol to arabitol when strains were grown on glucose. Further deletion of the mannitol dehydrogenase gene eliminated both polyols regardless of whether cells were grown in glucose or fructose. As a result, the modified Aureobasidium strains could be utilized to secrete exclusively arabitol-containing liamocin.