INVESTIGATION OF POLY(BETA-L-MELIC ACID) PRODUCTION BY STRAINS OF AUREOBASIDIUM-PULLULANS

Eight strains of the genus Aureobasidium obtained from culture collect ions were tested for their capability to produce poly(beta-L-malic aci d) (PMA). Four of the tested strains showed positive results. The most productive strain, A. pullulans CBS 591.75, was used to study the pro duction of PMA in stirred-tank reactors. It was found that PMA was mai nly produced in the late exponential phase, and the production related positively to glucose consumption. At the beginning of the fermentati on the pH increased from 4.0 to about 7.0; subsequently the pH decreas ed and remained stable at around 3.0-3.5 for several days. Temperature s higher than 25 degrees C were detrimental to PMA production and cell growth. PMA production and cell growth at 20 degrees C and 25 degrees C exhibited no significant dif ferences. PMA production and cell grow rh were studied under pH-controlled fermentation (at pH 2.0, 4.0, 5.5 ). The highest PMA production occurred at pH 4.0. PMA production was r educed at pH 2.0 although quite reasonable cell growth occurred at thi s pH value. Under optimized conditions 9.8 g PMA/l was produced during 9 days of fermentation in the stirred-tank reactors with an overall y ield of 0.11 g PMA/g glucose. A procedure for the isolation of PMA and its separation from the other components of the fermentation broth wa s developed. The isolated PMA was characterized by H-1 and C-13-NMR sp ectroscopy as well as by infrared absorption spectroscopy. Gel-permeat ion chromatography revealed a relative molecular mass of approximately 3000-5000 by comparison with polyethylene glycol standards.