Magnesium ions in yeast: setting free the metabolism from glucose catabolite repression

In a recent work we showed that magnesium (Mg^II) plays an important role in industrial ethanol production, overcoming the negative effect of the excess of minerals, particularly copper, present in sugarcane juice, with a consequent increase in ethanol yield. This cation has been reported to be involved in several steps of yeast metabolism, acting mainly as a co-factor of several enzymes of fermentation metabolism and protecting yeast cells from stressful conditions. However, despite many physiological investigations, its effect in the molecular mechanisms that control such metabolic activities remains unclear and to date no information concerning its influence on gene expression has been provided. The present work took advantage of the DNA microarray technology to analyse the global gene expression in yeast cells upon fermentation in Mg^II-supplemented medium. The results of the fermentation parameters confirmed the previous report on the increase in ethanol yield by Mg^II. Moreover, the gene expression data revealed an unexpected set of up-regulated genes currently assigned as being negatively-regulated by glucose, which belong to respiratory and energy metabolism, the stress response and the glyoxalate cycle. On the other hand, genes involved in ribosome biogenesis were down-regulated. Computational analysis provided evidence for a regulatory network commanded by key transcriptional factors that may be responsible for the biological action of Mg^II in yeast cells. In this scenario, Mg^II seems to act by reprogramming the yeast metabolism by releasing many genes from glucose catabolite repression with positive consequences for ethanol production and maintenance of cell viability.