Production of novel antistreptococcal liamocins by fermentation of agricultural biomass

Liamocins are unique heavier-than-water “oils” produced by certain strains of the fungus Aureobasidium pullulans.  Liamocins have antibacterial activity with specificity for Streptococcus sp.  Previous studies reported that liamocin yields were highest from strains of A. pullulans belonging to phylogenetic clades 8, 9, and 11, cultured on a specific basal medium containing sucrose.  In this study, 26 strains of A. pullulans from these clades were examined for the first time for production of liamocins from agricultural biomass substrates.  After seven days of growth, four strains produced at least 1.5 g of liamocins/L from medium containing 5% (w/v) alkaline hydrogen peroxide-pretreated wheat straw as a sole carbon source.   Liamocins produced from wheat straw were free of the melanin contamination common in sucrose-grown cultures.  Furthermore, MALDI-TOF MS analysis showed that liamocins produced from wheat straw were underacetylated, resulting in higher proportions of the mannitol-B1 species of liamocin, which has the highest biological activity against Streptococcus sp.  Production of liamocins from low-cost agricultural biomass might be particularly appropriate for bulk agricultural applications, such as in dairy cattle dips for prevention of mastitis caused by Streptococcus sp.