Enhanced production of Ca2+-polymalate (PMA) with high molecular mass by Aureobasidium pullulans var. pullulans MCW

Background: Polymalic acid (PMA) has many applications in food and medical industries. However, so far it has not been commercially produced by fermentation. Therefore, it is very important how to develop an economical process for a large scale production of PMA by one step fermentation. Results: After over 200 strains of Aureobasidium spp. isolated from the mangrove systems in the South of China were screened for their ability to produce Ca2+-polymalate (PMA), it was found that Aureobasidium pullulans var. pullulans MCW strain among them could produce high level of Ca2+-PMA. The medium containing only 140.0 g/L glucose, 65.0 g/L CaCO3 and 7.5 g/L corn steep liquor was found to be the most suitable for Ca2+-PMA production. Then, 121.3 g/L of Ca2+-PMA was produced by A. pullulans var. pullulans MCW strain within 120 h at flask level. During 10-L batch fermentation, 152.52 g/L of Ca2+-PMA in the culture and 8.6 g/L of cell dry weight were obtained within 96 h, leaving 4.5 g/L of reducing sugar in the fermented medium. After purification of the Ca2+-PMA from the culture and acid hydrolysis of the purified Ca2+-PMA, HPLC analysis showed that A. pullulans var. pullulans MCW strain produced only one main component of Ca2+-PMA and the hydrolysate of the purified Ca2+-PMA was mainly composed of L-malic acid. Mw (the apparent molecular weight) of the purified PMA was 2.054 x 10(5) (g/moL) and the purified PMA was estimated to be composed of 1784 L-malic acids. Conclusions: It was found that A. pullulans var. pullulans MCW strain obtained in this study could yield 152.52 g/L of Ca2+-PMA within the short time, the produced PMA had the highest molecular weight and the medium for production of Ca2+-PMA by this yeast was very simple.