Production of novel antibacterial liamocins by strains of Aureobasidium pullulans

Certain strains of Aureobasidium pullulans produce liamocins, heavier-than-water “oils” that accumulate in liquid cultures.  Liamocins are surface active, and inhibit mammalian cancer cell lines.  Recently, we discovered that liamocins have antibacterial activity with specificity against Streptococcus sp.  In a survey of more than 50 phylogenetically diverse strains of A. pullulans, 21 produced liamocins.  Highest yields were obtained from strains in phylogenetic clades 8, 9, and particularly 11.  Additional strains were isolated from these clades and shown to be good sources of liamocins.  Five representative strains were tested for liamocin production on four different media.   Best growth and highest liamocin yields were obtained using A. pullulans strain NRRL 50384 grown in the previously described medium, PM, which contains 5% (w/v) sucrose.  Unexpectedly, the choice of strain and basal medium affected not only culture growth and liamocin yields, but also the structure of liamocins produced.  For example, A. pullulans strain NRRL 50380 grown on PM-sucrose produced four types of liamocins with unique chemical structures, consisting of a single mannitol headgroup partially O-acylated with polyester tails containing three or four 3,5-dihydroxydecanoic ester groups, some of which were acetylated. These variant structures exhibited slightly different antibacterial activities.   Liamocins from other strains and media varied not only in the ratios of trimer and tetramer tail groups, but also in the nature of the polyol headgroup, which could include glycerol and/or arabitol.  Liamocins produced by strains of A. pullulans have potential agricultural and pharmaceutical applications as antibacterials with specificity against Streptococcus sp.