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 flux through glycolysis. We have investigated the possibility of control of this flux by trehalose 6-phosphate, an inhibitor of hexokinase of Saccharomyces cerevisiae and other eukaryotes (Blasquez et al., FEBS Lett. (1993) 329, 51-54). Hexokinase of A. niger was shown in vitro to be only weakly inhibited by trehalose 6-phosphate (KI 1.5-2 mM). To investigate the in vivo relevance of this inhibition, we used isogenic strains of A. niger, carrying either a disruption or an amplification of the trehalose-6-phosphate synthase A (T6PSA)-encoding gene (ggsA) and exhibiting corresponding differences in T6PSA activity. These strains 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 strain initiated citric acid accumulation earlier, whereas the multicopy strain showed the reverse effect. When sucrose was replaced by lactose, which enabled only low rates of catabolism irrespective of its concentration (1-8%), no differences in the initiation or rate of citric acid 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.