EFFECT OF PH ON PULLULAN PRODUCTION RELATIVE TO CARBON SOURCE AND YEAST EXTRACT COMPOSITION OF GROWTH-MEDIUM

The effect of medium pH on pullulan synthesis by Aureobasidium pullula ns ATCC 42023 was investigated. The pH of a phosphate-buffered minimal medium, in which either sucrose or corn syrup was added as a carbon s ource, was varied from 2.0 to 7.5. In batch shake cultures, pullulan c oncentration was monitored over a period of 5 days at 30-degrees-C. Th e lowest pullulan concentration was detected at pH 2.0 for both carbon sources in a media which either contained or lacked yeast extract. Th e level of pullulan found for either carbon sources increased as the c ulture medium pH was elevated toward neutrality. The optimal initial p H of the medium differed with respect to the carbon source and to the presence of yeast extract. The optimal pH for pullulan elaboration by the fungus after growth on medium containing yeast extract and sucrose was 6.5. In the absence of yeast extract in the medium, the optimal i nitial pH decreased to 5.5. A broad pH optimum was found when ATCC 420 23 was grown on a corn syrup-containing culture medium which was suppl emented with yeast extract. Fungal pullulan elaboration was optimal be tween pH 5.0 and 7.0 in this medium. In the absence of yeast extract, the optimal range for pullulan synthesis by A. pullulans decreased to between 3.5 and 5.0.