Overproduction of poly(β-malic acid) (PMA) from glucose by a novel Aureobasidium sp. P6 strain isolated from mangrove system.

After over 100 strains of Aureobasidium spp isolated from mangrove system were screened for their ability to produce poly(β-malic acid) (PMA), it was found that Aureobasidium sp. P6 strain among them could produce high level of Ca(2+)-PMA. Fourteen percent glucose and 6.5 % CaCO3 in the medium were the most suitable for Ca(2+)-PMA production. Then, 100.7 g/l of Ca(2+)-PMA was produced using Aureobasidium sp. P6 strain within 168 h at flask level. During 10-l batch fermentation, when the medium contained 12.0 % glucose, 98.7 g/l of Ca(2+)-PMA in the culture and 14.7 g/l of cell dry weight were obtained within 156 h, leaving 0.34 % reducing sugar in the fermented medium. When glucose concentration in the fermentation medium was 14.0 %, 118.3 g/l of Ca(2+)-PMA in the culture and 16.4 g/l of cell dry weight were obtained within 168 h, leaving 0.4 % reducing sugar in the fermented medium. After purification of Ca(2+)-PMA from the culture and acid hydrolysis of the pure Ca(2+)-PMA, analysis of HPLC showed that Aureobasidium sp. P6 strain only produced two main components of Ca(2+)-PMA and minor amount of calcium malate and that the hydrolysate of PMA was mainly composed of calcium malate. This is the first time to report that the novel yeast strain Aureobasidium sp. P6 strain isolated from the mangrove systems can produce such high amount of Ca(2+)-PMA.