Aspergillus niger cyclic AMP levels are not influenced by manganese deficiency and do not correlate with citric acid accumulation

Summary The role of intracellular levels of cyclic AMP in the control of citic acid accumulation by Aspergillus niger has been investigated. For this purpose, A. niger was grown in media containing either high (14%, w/v) or low (2%, w/v) concentrations of sucrose, supplemented with 10 M Mn²⁺ (manganese-sufficient) or not (manganese-deficient), to obtain conditions leading to variable citrate accumulation. Citric acid accumulation was only observed in high-sugar, manganese-deficient medium. Intracellular levels of cyclic AMP were significantly higher in mycelia grown on low-sugar media, but were not significantly influenced by the absence of manganese ions. When sucrose in the high-sugar medium was substituted by other mono- or disaccharides, similar intracellular concentrations of cyclic AMP were observed. However, citric acid accumulation was only significant with sucrose, glucose and fructose. It is thus concluded that the intracellular level of cyclic AMP is not causally related to the accumulation of citric acid by the fungus, and —noteworthy — is not affected by manganese deficiency (despite adenylate cyclase reputed to be a manganese-requiring enzyme).Offprint requests to: C. P. Kubicek