Cold Stress in Antarctic Fungi Targets Enzymes of the Glycolytic Pathway and Tricarboxylic Acid Cycle

To evaluate the concept of metabolic cold adaptation in Antarctic fungi, we compared the activities of several key enzymes of the glycolytic pathway and the TCA cycle (hexokinase, glucose-6-phosphate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, succinate dehydrogenase, isocitrate dehydrogenase, and malate dehydrogenase) in psychrotolerant Penicillium sp. 161 and mesophilic Aspergillus glaucus 363 during both the stress exposure (6 h) and recovery phases. Mycelia of the Antarctic strains, grown until middle exponential phase at optimal temperature, were shifted to colder temperatures, i.e., 4 and 10 °C. Our investigations showed a re-routing of carbon metabolism away from glycolysis into the pentose phosphate pathway (PPP), which serves as a cellular stress-resistance mechanism under cold stress conditions. Moreover, the data clearly suggest strain-dependent differences in cold stress response concerning TCA enzyme activities between both fungi. The psychrotolerant strain induces glyoxalate cycle activities and the mesophilic strain uses a reduction of respiratory activity. A recovery response after removal of the stress factor was observed.