1. Introduction
Saccharomyces cerevisiae is a facultative anaerobe able to live on
various fermentable and non-fermentable carbon sources. When
yeast is grown on fermentable substrates such as glucose, the
metabolic energy essentially originates from glycolysis. The Pasteur
effect relates oxygen with sugar catabolism, hence glycolysis in
resting cells proceeds more rapidly under anaerobic conditions than
under aerobic conditions [1]. Fermentation is the predominant route
of sugar metabolism in growing cultures. If the glucose concentration
is high, the Pasteur effect is no longer operable and is replaced by the
Crabtree effect, by which cells continue to ferment [2]. The Crabtree
effect can be either a short-term or a long-term effect [3]. The shortterm
effect is characterized by its capability of triggering alcoholic
fermentation upon a sudden glucose excess condition whereas the
long-term effect is characterized by the respiratory fermentative
metabolism observed in batch cultivation or in continuous culturing
[4]. In S. cerevisiae, growth in rich media with low glucose
concentration increases both replicative and chronological longevity
[5,6]. The beneficial effects of glucose restriction in yeast are related to
the increase in respiratory rates occurring when glucose levels in the
media are low [7,8]. These enhanced respiratory rates increase
intracellular NAD+ levels which may be involved in the regulation
of replicative lifespan. This modulates the activity of sir2 family
proteins [9] and reduces the releasing of mitochondrial reactive
oxygen species (ROS) [10]. ROS are normal by-products of cell
metabolism; however, an increase in their production can cause
oxidative modifications in cell macromolecules such as proteins, DNA
and lipids.