To select a Saccharomyces cerevisiae reference strain amenable to experimental techniques used in (molecular) genetic, physiological and biochemical engineering research, a variety of properties were studied in four diploid, prototrophic laboratory strains. The following parameters were investigated: 1) maximum specific growth rate in shake-flask cultures; 2) biomass yields on glucose during growth on defined media in batch cultures and steady-state chemostat cultures under controlled conditions with respect to pH and dissolved oxygen concentration; 3) the critical specific growth rate above which aerobic fermentation becomes apparent in glucose-limited accelerostat cultures; 4) sporulation and mating efficiency; and 5) transformation efficiency via the lithium-acetate, bicine, and electroporation methods. On the basis of physiological as well as genetic properties, strains from the CEN.PK family were selected as a platform for cell-factory research on the stoichiometry and kinetics of growth and product formation.

Background: Real-time RT-PCR is the recommended method for quantitative gene expression analysis. A compulsory step is the selection of good reference genes for normalization. A few genes often referred to as HouseKeeping Genes (HSK), such as ACT1, RDN18 or PDA1 are among the most commonly used, as their expression is assumed to remain unchanged over a wide range of conditions. Since this assumption is very unlikely, a geometric averaging of multiple, carefully selected internal control genes is now strongly recommended for normalization to avoid this problem of expression variation of single reference genes. The aim of this work was to search for a set of reference genes for reliable gene expression analysis in Saccharomyces cerevisiae.

The yeast Saccharomyces cerevisiae can synthesize trehalose and also use this disaccharide as a carbon source for growth. However, the molecular mechanism by which extracellular trehalose can be transported to the vacuole and degraded by the acid trehalase Ath1p is not clear. By using an adaptation of the assay of invertase on whole cells with NaF, we showed that more than 90% of the activity of Ath1p is extracellular, splitting of the disaccharide into glucose. We also found that Agt1p-mediated trehalose transport and the hydrolysis of the disaccharide by the cytosolic neutral trehalase Nth1p are coupled and represent a second, independent pathway, although there are several constraints on this alternative route. First, the AGT1/MAL11 gene is controlled by the MAL system, and Agt1p was active in neither non-maltose-fermenting nor maltose-inducible strains. Second, Agt1p rapidly lost activity during growth on trehalose, by a mechanism similar to the sugar-induced inactivation of the maltose permease. Finally, both pathways are highly pH sensitive and effective growth on trehalose occurred only when the medium was buffered at around pH 5.0. The catabolism of trehalose was purely oxidative, and since levels of Ath1p limit the glucose flux in the cells, batch cultures on trehalose may provide a useful alternative to glucose-limited chemostat cultures for investigation of metabolic responses in yeast. Trehalose [␣-D-glucopyranosyl-(1-1)-␣-D-glucopyranoside] is a nonreducing disaccharide of glucose discovered in 1832 byWiggers in a mushroom crop and later in many other fungi, plants, and insects (13). In the yeast Saccharomyces cerevisiae, trehalose can accumulate up to 15% of the cell dry mass, depending on the growth conditions, the stage of the life cycle, or environmental stress (2, 27), and for this reason it has been considered a storage carbohydrate (15,27). Moreover, the ability of this disaccharide to protect proteins and biological membranes against adverse conditions suggests that it also plays a stress-protectant role in this yeast (49,50) and probably in other organisms that produce it (14).Intracellular levels of trehalose result from a well-controlled balance between enzymatic synthesis and degradation. In the yeast S. cerevisiae, the synthesis of trehalose is catalyzed by a UDP-glucose-dependent trehalose synthase (TPS) protein complex encoded by four genes. TPS1 and TPS2 encode trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase, respectively, while TPS3 and TSL1 code for two regulatory subunits of the TPS complex (for a review, see reference 15). Hydrolysis of trehalose into glucose can be carried out by at least two enzymes: a cytosolic or neutral trehalase encoded by NTH1 (26) and a vacuolar or acid trehalase (25, 28) encoded by ATH1 (12). The yeast genome also harbors the NTH2 gene, whose product is 77% identical to Nth1p, but until now, no trehalase activity has been associated with this protein (37). The neutral trehalase Nth1p is responsible for the intracellular mobilization ...

The dynamic responses of reserve carbohydrates with respect to shortage of either carbon or nitrogen source was studied to obtain a sound basis for further investigations devoted to the characterization of mechanisms by which the yeast Saccharomyces cerevisiae can cope with nutrient limitation during growth. This study was carried out in well‐controlled bioreactors which allow accurate monitoring of growth and frequent sampling without disturbing the culture. Under glucose limitation, genes involved in glycogen and trehalose biosynthesis (GLG1, GSY1, GSY2, GAC1, GLC3, TPS1 ), in their degradation (GPH1, NTH1 ), and the typical stress‐responsive CTT1 gene were coordinately induced in parallel with glycogen, when the growth has left the pure exponential phase and while glucose was still plentiful in the medium. Trehalose accumulation was delayed until the diauxic shift, although TPS1 was induced much earlier, due to hydrolysis of trehalose by high trehalase activity. In contrast, under nitrogen limitation, both glycogen and trehalose began to accumulate at the precise time when the nitrogen source was exhausted from the medium, coincidentally with the transcriptional activation of genes involved in their metabolism. While this response to nitrogen starvation was likely mediated by the stress‐responsive elements (STREs) in the promoter of these genes, we found that these elements were not responsible for the co‐induction of genes involved in reserve carbohydrate metabolism during glucose limitation, since GLG1, which does not contain any STRE, was coordinately induced with GSY2 and TPS1. Copyright © 1999 John Wiley & Sons, Ltd.

It has been known for a long time that the yeast Saccharomyces cerevisiae can assimilate ␣-methylglucopyranoside and isomaltose. We here report the identification of 5 genes (YGR287c, YIL172c, YJL216c, YJL221c and YOL157c), which, similar to the SUCx, MALx, or HXTx multigene families, are located in the subtelomeric regions of different chromosomes. They share high nucleotide sequence identities between themselves (66 -100%) and with the MALx2 genes (63-74%). Comparison of their amino acid sequences underlined a substitution of threonine by valine in region II, one of the four highly conserved regions of the ␣-glucosidase family. This change was previously shown to be sufficient to discriminate ␣-1,4-to ␣-1,6-glucosidase activity in YGR287c (Yamamoto, K., Nakayama, A., Yamamoto, Y., and Tabata, S. (2004) Eur. J. Biochem. 271, 3414 -3420). We showed that each of these five genes encodes a protein with ␣-glucosidase activity on isomaltose, and we therefore renamed these genes IMA1 to IMA5 for IsoMAltase. Our results also illustrated that sequence polymorphisms among this family led to interesting variability of gene expression patterns and of catalytic efficiencies on different substrates, which altogether should account for the absence of functional redundancy for growth on isomaltose. Indeed, deletion studies revealed that IMA1/YGR287c encodes the major isomaltase and that growth on isomaltose required the presence of AGT1, which encodes an ␣-glucoside transporter. Expressions of IMA1 and IMA5/ YJL216c were strongly induced by maltose, isomaltose, and ␣-methylglucopyranoside, in accordance with their regulation by the Malx3p-transcription system. The physiological relevance of this IMAx multigene family in S. cerevisiae is discussed.Gene duplication, one of the main driving forces in genome evolution, generates paralogous genes that can acquire specificities by sequence divergence. These redundant genes are defined as multigene families, the most often located within subtelomere sequences. Very recently, Brown and coworkers demonstrated that the extraordinary instability of these regions supports rapid adaptation to novel niches.

The plant pathogen Ralstonia solanacearum possesses two genes encoding a trehalose-6-phosphate synthase (TPS), an enzyme of the trehalose biosynthetic pathway. One of these genes, named ripTPS, was found to encode a protein with an additional N-terminal domain which directs its translocation into host plant cells through the type 3 secretion system. RipTPS is a conserved effector in the R. solanacearum species complex, and homologues were also detected in other bacterial plant pathogens. Functional analysis of RipTPS demonstrated that this type 3 effector synthesizes trehalose-6-phosphate and identified residues essential for this enzymatic activity. Although trehalose-6-phosphate is a key signal molecule in plants that regulates sugar status and carbon assimilation, the disruption of ripTPS did not alter the virulence of R. solanacearum on plants. However, heterologous expression assays showed that this effector specifically elicits a hypersensitive-like response on tobacco that is independent of its enzymatic activity and is triggered by the C-terminal half of the protein. Recognition of this effector by the plant immune system is suggestive of a role during the infectious process.

In the yeast Saccharomyces cerevisiae, the synthesis of endogenous trehalose is catalyzed by a trehalose synthase complex, TPS, and its hydrolysis relies on a cytosolic/neutral trehalase encoded by NTH1. In this work, we showed that NTH2, a paralog of NTH1, encodes a functional trehalase that is implicated in trehalose mobilization. Yeast is also endowed with an acid trehalase encoded by ATH1 and an H ؉ /trehalose transporter encoded by AGT1, which can together sustain assimilation of exogenous trehalose. We showed that a tps1 mutant defective in the TPS catalytic subunit cultivated on trehalose, or on a dual source of carbon made of galactose and trehalose, accumulated high levels of intracellular trehalose by its Agt1p-mediated transport. The accumulated disaccharide was mobilized as soon as cells entered the stationary phase by a process requiring a coupling between its export and immediate extracellular hydrolysis by Ath1p. Compared to what is seen for classical growth conditions on glucose, this mobilization was rather unique, since it took place prior to that of glycogen, which was postponed until the late stationary phase. However, when the Ath1p-dependent mobilization of trehalose identified in this study was impaired, glycogen was mobilized earlier and faster, indicating a fine-tuning control in carbon storage management during periods of carbon and energy restriction.Trehalose is a nonreducing disaccharide of ␣(1,1)-linked glucose present in many organisms, including bacteria, fungi, insects, and plants (12). Fungal cells can accumulate this disaccharide to up to 15% of the cell dry mass depending on growth conditions and environmental stress (for a review, see reference 15). Genetic and metabolic studies led to the proposal that trehalose plays two distinct functions in living cells. On the one hand, it acts as a stress protectant of proteins and biological membranes against adverse conditions (39). On the other hand, it may play a role as a storage carbohydrate in the yeast Saccharomyces cerevisiae. This latter function was suggested by the rapid mobilization of intracellular trehalose upon the resumption of growth of starved cells on a fresh glucose medium and during spore maturation and germination, as well as during oscillatory events in continuous or batch yeast cultures (22,28). Trehalose is also consumed very slowly when cells are maintained in nongrowing conditions, and this breakdown often follows that of glycogen, the major storage carbohydrate in yeast (26, 32), although the mobilization pattern of one glucose store before the other can be dependent on the growth conditions (17, 34, 37).In the yeast S. cerevisiae, the intracellular level of trehalose is the result of a well-regulated balance between enzymatic synthesis and degradation. The synthesis of trehalose is catalyzed by an UDP-glucose-dependent trehalose synthase (TPS) protein complex encoded by four genes. TPS1 and TPS2 encode the trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase, respectively, and TPS3 and TSL1 ...

Background: Decades of observations strengthened the idea that trehalose is a chemical chaperone. Results: A catalytically inactive variant of the trehalose-6P synthase (Tps1) maintains cell survival and energy homeostasis under stress exposure. Conclusion: The Tps1 protein itself, not trehalose, is crucial for cell integrity. Significance: This work provides unbiased evidence for an alternative function of Tps1, a new "moonlighting" protein.