Carbohydrate and energy-yielding metabolism in non-conventional yeasts: Figure 1

Abstract

Sugars are excellent carbon sources for all yeasts. Since a vast amount of information is available on the components of the pathways of sugar utilization in Saccharomyces cerevisiae it has been tacitly assumed that other yeasts use sugars in the same way. However, although the pathways of sugar utilization follow the same theme in all yeasts, important biochemical and genetic variations on it exist. Basically, in most non-conventional yeasts, in contrast to S. cerevisiae, respiration in the presence of oxygen is prominent for the use of sugars. This review provides comparative information on the different steps of the fundamental pathways of sugar utilization in non-conventional yeasts: glycolysis, fermentation, tricarboxylic acid cycle, pentose phosphate pathway and respiration. We consider also gluconeogenesis and, briefly, catabolite repression. We have centered our attention in the genera Kluyveromyces, Candida, Pichia, Yarrowia and Schizosaccharomyces, although occasional reference to other genera is made. The review shows that basic knowledge is missing on many components of these pathways and also that studies on regulation of critical steps are scarce. Information on these points would be important to generate genetically engineered yeast strains for certain industrial uses.

Evolutionary principles of modular gene regulation in yeasts

“…Differences in trans regulators may further contribute to the reassignment of their targets between modules. While many of the regulators of glucose repression in S. cerevisiae are present across the phylogeny (Flores et al, 2000), the regulation of some has changed at the WGD and at the ancestor of the Schizosaccharomyces , consistent with the reassignment of their targets. For example, the glucose repressing MIG genes and the TUP1-CYC8 complex are strongly repressed following glucose depletion in most post-WGD species, whereas some respiration activators are strongly induced ( CAT8 and HAP2,4,5 and SIP2 post-WGD, HAP2 , MOT3 , and SIP2 in S. pombe , data not shown).…”

The high fermentative metabolism of Kluyveromyces marxianus UFV-3 relies on the increased expression of key lactose metabolic enzymes

“…It has been shown that the expression of the pyruvate decarboxylase gene rapidly increased in K. marxianus under hypoxic conditions. Some authors reported that the expression of the gene that encodes pyruvate decarboxylase in S. cerevisiae also increases, although it rapidly decreases after the initial stimulus (Flores et al 2000). Similar to the scenario in S. cerevisiae (Brink et al 2008), high carbohydrate concentrations and low oxygen levels increased the expression of the pyruvate decarboxylase gene in K. marxianus UFV-3.…”

“…Similar to the gene that expresses b-galactosidase, the pyruvate decarboxylase gene was also highly expressed in K. marxianus UFV-3 under hypoxic conditions. Pyruvate decarboxylase is a key enzyme of the fermentative pathway in yeasts (Flores et al 2000), and its disruption has been shown to block ethanol production in S. cerevisiae (Ishida et al 2006). It has been shown that the expression of the pyruvate decarboxylase gene rapidly increased in K. marxianus under hypoxic conditions.…”

“…The final product of the glycolytic pathway is pyruvate, which is a pivotal product of this pathway because the microbial metabolism diverges from pyruvate to either respiration or fermentation. The total or partial oxidation of any carbohydrate depends on enzymatic regulation with pyruvate as the substrate (Flores et al 2000). Despite the consensus about Kluyveromyces lactose metabolism, there is no research on enzymatic activity or gene expression in the K. marxianus fermentative pathway.…”

The dimorphic yeast Yarrowia lipolytica possesses an atypical phosphofructokinase: characterization of the enzyme and its encoding gene

“…Among them are its unusual ability to grow on hydrocarbons, its ability to excrete important organic acids, its potential as a host for the expression of heterologous proteins (for reviews see Barth & Gaillardin, 1996), and its ability to shift between a yeast and a hyphal form (Domínguez et al, 2000). In spite of its basic and industrial interest, biochemical studies on its central metabolic pathways are scarce (Flores et al, 2000). Regarding the regulatory steps of glycolysis, a pathway nearly ubiquitous in all life forms, it is known only that the hexokinase activity of Y. lipolytica is low, about 1/10 of that of Saccharomyces cerevisiae (Petit & Gancedo, 1999), and that it is strongly inhibited by trehalose 6-phosphate (Petit & Gancedo, 1999), and that pyruvate kinase exhibits kinetic and regulatory properties significantly different from those of the enzyme from S. cerevisiae (Hirai et al, 1975).…”