Biosynthetic pathways of glycerol accumulation under salt stress in Aspergillus nidulans

A culture of Aspergillus nidulans (FGSC 359) was gradually adapted for growth in media containing up to 2 M NaCl or was exposed to a salt shock with 2 M NaCl. The intracellular glycerol level increased by about 7.9-fold in salt-adapted and 2.4-fold in salt-shocked cultures when compared to the unadapted culture. The biosynthetic pathway involved in the accumulation of glycerol was investigated under long-term salt adaptation and short-term salt shock. Glycerol-3-phosphate dehydrogenase (EC 1.1.1.8) was induced 1.4-fold in salt-shocked but not in salt-adapted cultures. An alternate enzymatic pathway involving glycerol dehydrogenase (NADP(+)-dependent) utilizing dihydroxyacetone (DHA) and/or DL-glyceraldehyde (DL-GAD) was induced by NaCl. DHA-dependent glycerol dehydrogenase activity was induced about 6.3-fold in salt-adapted and 1.35-fold in salt-shocked cultures, while DL-GAD-dependent activity was induced about 6.1-fold in salt-adapted and 1.2-fold in salt-shocked cultures. However, the level of glycerol dehydrogenase activity with DL-GAD as substrate was 7% of the DHA-dependent activity. We conclude that a salt-inducible NADP(+)-dependent glycerol dehydrogenase activity electrophoretically indistinguishable from previously described glycerol dehydrogenase I results in glycerol accumulation in salt-stressed A. nidulans.