STIMULATION OF CITRIC-ACID PRODUCTION IN ASPERGILLUS-NIGER BY ADDITION OF VISCOUS SUBSTANCES IN SHAKE CULTURE

When glucose (120 mg/ml) was used as a carbon source, Aspergillus nige r Yang no. 2. showed a markedly low citric acid productivity in shake culture (15.4 mg/ml) but a high productivity in semi-solid and surface cultures (72.3 mg/ml and 67.6 mg/ml, respectively). Since the viscosi ty of the medium was assumed to be one of the important factors for ci tric acid productivity in shake culture, the effects of the addition o f viscous substances on citric acid productivity of strain Yang no. 2 were examined. The addition of 2.0-6.0 mg gelatin/ml as a viscous addi tive to the medium containing glucose as a carbon source increased sli ghtly the medium viscosity but substantially increased the citric acid productivity in shake culture to levels of 52.0-53.3 mg/ml, about 3.4 times as much as that without gelatin. However, no influence of gelat in addition was observed in semi-solid and surface cultures, i.e. unde r static cultivation conditions. Different mycelial morphologies of th e strain were observed when cultivations were done in shake culture wi th or without the addition of gelatin. Addition of 5.0 mg agar/ml, 5.0 mg carageenan/ml 2.5 mg carboxymethylcellulose/ml and 2.5 mg polyethy lene glycol 6000/ml, to the medium containing glucose as a carbon sour ce also increased the citric acid productivity in shake culture to lev els of 39.2-54.7 mg/ml. Since Yang no. 2 does not utilize these viscou s substances, these results suggested that the viscous substances func tioned as protectants for the mycelium from physiological stresses due to shaking and as a consequence resulted in a remarkably increased ci tric acid productivity in shake culture.