TREHALOSE-6-PHOSPHATE SYNTHASE-A AFFECTS CITRATE ACCUMULATION BY ASPERGILLUS-NIGER UNDER CONDITIONS OF HIGH GLYCOLYTIC FLUX

Accumulation of citric acid by Aspergillus niger depends on a high flu x through glycolysis. We have investigated the possibility of control of this flux by trehalose 6-phosphate, an inhibitor of hexokinase of S accharomyces cerevisiae and other eukaryotes (Blasquez et al., FEES Le tt. (1993) 329, 51-54). Hexokinase of A. niger was shown in vitro to b e only weakly inhibited by trehalose 6-phosphate (K-I 1.5-2 mM). To in vestigate the in vivo relevance of this inhibition, we used isogenic s trains of A. niger, carrying either a disruption or an amplification o f the trehalose-6-phosphate synthase A (T6PSA)-encoding gene (ggsA) an d exhibiting corresponding differences in T6PSA activity. These strain s produced citric acid at comparable rates and with similar yields on 1 or 2.5% (w/v) sucrose. At 5-14% (w/v) sucrose, the ggsA disrupted st rain initiated citric acid accumulation earlier, whereas the multicopy strain showed the reverse effect. When sucrose was replaced by lactos e, which enabled only low rates of catabolism irrespective of its conc entration (1-8%), no differences in the initiation or rate of citric a cid accumulation were observed between the three strains. The possible mechanisms by which ggsA controls glycolytic flux in A. niger in the presence of high sugar concentrations are discussed.