Fermentative Production of Poly(β-L-malic acid), a Polyelectrolytic Biopolyester, by Aureobasidium sp.

Abstract

Many strains of a black yeast, identified as Aureobasidium sp., were isolated by a selective medium, which contained mannitol as a main carbon source, and found to produce an extracellular biopolyester from glucose. The biopolyester was recovered as its calcium salt (61g) from culture filtrate (1 liter). The acid hydrolysis and the transmethylation of the polyester proved L-malic acid to be its monomeric repeating unit. The saponification of the polyester, however, gave fumaric and maleic acids in about 20% yield, in addition to the malic acid. ¹H NMR analysis proved the main-chain ester linkage of the polyester to be β-type. The apparent molecular mass was estimated to be distributed between about 6 and 11 kDa in a buffer (pH 6.8) with a high ionic strength (0.2M).