Efficient transformation of inulin into liamocins by a mutant of Aureobasidium melanogenum HN6-1 and antimicrobial activity of the produced Massoia lactone.

Inulin is a β-2,1-linked D-fructofuranose macromolecule that is terminated by a glucose residue. The simultaneous overexpression of the PYC1 gene encoding pyruvate carboxylase, the ACL1 gene encoding ATP-citrate lyase and the INU1 gene encoding inulinase in A. melanogenum HN6-1 resulted in an overexpressing strain U3 producing 80.7 U/mL of inulinase activity and 50.7 ± 1.9 g/L of liamocins at the flask level. Concurrently, the overexpressing strain U3 exhibited higher mannitol accumulation in its cells than its parent strain A15. In a 10-L fermentation, the overexpressing strain U3 efficiently converted inulin to yield 55.2 ± 3.3 g/L of liamocins, producing 84.1 ± 0.54 U/mL of inulinase activity, and 15.2 ± 0.41 g/L of cell mass, resulting in a yield of 0.34 g/g of inulin and a productivity of 0.46 g/h/L. Hence, 99.7 % of the total sugar (inulin) was utilized for cell growth, inulinase production, and liamocins production. The Massoia lactone released and purified from the produced liamocins demonstrated significant inhibitory effects on the cell growth of Enterobacter cloacae and Candida albicans.