Transcriptional regulation of the Schizosaccharomyces pombe malic enzyme gene, mae2

Selection and characterization of a Patagonian Pichia kudriavzevii for wine deacidification

AIMS

The purpose of this study was to select autochthonous yeasts with metabolic ability to degrade L-malic acid for its potential use in young wine deacidification.

METHODS AND RESULTS

Fifty seven Patagonian nonSaccharomyces yeast of oenological origin were identified by conventional molecular methods and tested in their capability to grow at the expense of L-malic acid. Only four isolates belonging to Pichia kudriavzevii species showed this property, and one of them was selected to continue with the study. This isolate, named as P. kudriavzevii ÑNI15, was able to degrade L-malic acid in microvinifications, increasing the pH 0·2-0·3 units with a minimal effect on the acid structure of wine. Additionally, this isolate produced low levels of ethanol, important levels of glycerol (10·41 ± 0·48 g l(-1) ) and acceptable amounts of acetic acid (0·86 ± 0·13 g l(-1) ). In addition, it improved the sensorial attributes of wine increasing its fruity aroma.

CONCLUSIONS

The selection of yeasts for oenological use among nonSaccharomyces species led to the finding of a yeast strain with novel and interesting oenological characteristics which could have significant implications in the production of well-balanced and more physicochemical and microbiological stable young wines.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of P. kudriavzevii ÑNI15 as mixed starter with S. cerevisiae would eliminate the cultural and cellar operations undertaken to adjust the musts acidity, therefore improving wine quality and reducing production costs.

Analysis of aldosterone-induced differential receptor-independent protein patterns using 2D-electrophoresis and mass spectrometry

In the human body the mineralocorticoid aldosterone is responsible for maintaining water and electrolyte homeostasis and therefore controlling blood pressure. In addition, aldosterone has recently been associated with severe heart failure. Besides receptor-dependent action, the damaging effects of aldosterone may also be partly mediated through non-genomic mechanisms. The present study focuses on the mineralocorticoid receptor-independent action of aldosterone at the protein level. We chose the fission yeast Schizosaccharomyces pombe as a model organism, since this yeast does not contain nuclear steroid receptors, but many genes and regulatory mechanisms that are close to those of mammals. Using 2D-electrophoresis we identified for the first time protein spots affected by aldosterone in a nuclear receptor-free system. Mass spectrometry analysis using MALDI-TOF MS and nanoLC-MS/MS approaches allowed the unambiguous identification of 11 proteins that showed increased or decreased levels, which may represent newly identified players and pathways of aldosterone-induced action. Two proteins with a connection to osmotic regulation (NAD-dependent malic enzyme and glycerol-3-phosphate-dehydrogenase), as well as two proteins involved in the overall organization of the cytoskeleton, vip1 and glyceraldehyde-3-phosphate dehydrogenase, which was also found to be specifically affected by aldosterone in human HCT116 cells, are discussed.

Cloning, characterisation, and heterologous expression of the Candida utilis malic enzyme gene

The Candida utilis malic enzyme gene, CME1, was isolated from a cDNA library and characterised on a molecular and biochemical level. Sequence analysis revealed an open reading frame of 1,926 bp, encoding a 641 amino acid polypeptide with a predicted molecular weight of approximately 70.2 kDa. The inferred amino acid sequence suggested a cytosolic localisation for the malic enzyme, as well as 37 and 68% homologies with the malic enzymes of Schizosaccharomyces pombe and Saccharomyces cerevisiae, respectively. Expression of the CME1 gene was subject to carbon catabolite repression and substrate induction, similar to the regulatory mechanisms observed for the C. utilis dicarboxylic acid permease. The CME1 gene was successfully expressed in S. cerevisiae under control of the S. cerevisiae PGK1 promoter and terminator. When coexpressed with the S. pombe malate permease gene (mae1), it resulted in a recombinant S. cerevisiae strain able to completely degrade 90% of the extracellular L-malate within 24 h.

Malo-ethanolic fermentation in Saccharomyces and Schizosaccharomyces

Yeast species are divided into the K(+) or K(-) groups, based on their ability or inability to metabolise tricarboxylic acid (TCA) cycle intermediates as sole carbon or energy source. The K(-) group of yeasts includes strains of Saccharomyces, Schizosaccharomyces pombe and Zygosaccharomyces bailii, which is capable of utilising TCA cycle intermediates only in the presence of glucose or other assimilable carbon sources. Although grouped together, these yeasts have significant differences in their abilities to degrade malic acid. Typically, strains of Saccharomyces are regarded as inefficient metabolisers of extracellular malic acid, whereas strains of Sch. pombe and Z. bailii can effectively degrade high concentrations of malic acid. The ability of a yeast strain to degrade extracellular malic acid is dependent on both the efficient transport of the dicarboxylic acid and the efficacy of the intracellular malic enzyme. The malic enzyme converts malic acid into pyruvic acid, which is further metabolised to ethanol and carbon dioxide under fermentative conditions via the so-called malo-ethanolic (ME) pathway. This review focuses on the enzymes involved in the ME pathway in Sch. pombe and Saccharomyces species, with specific emphasis on the malate transporter and the intracellular malic enzyme.

Differential malic acid degradation by selected strains of Saccharomyces during alcoholic fermentation

To produce a high-quality wine, it is important to obtain a fine balance between the various chemical constituents, especially between the sugar and acid content. The latter is more difficult to achieve in wines that have high acidity due to excess malic acid, since wine yeast in general cannot effectively degrade malic acid during alcoholic fermentation. An indigenous Saccharomyces paradoxus strain RO88 was able to degrade 38% of the malic acid in Chardonnay must and produced a wine of good quality. In comparison, Schizosaccharomyces pombe strain F effectively removed 90% of the malic acid, but did not produce a good-quality wine. Although commercially promoted as a malic-acid-degrading wine yeast strain, only 18% of the malic acid was degraded by Saccharomyces cerevisiae Lalvin strain 71B. Preliminary studies on the transcriptional regulation of the malic enzyme gene from three Saccharomyces strains, i.e. S. paradoxus RO88, S. cerevisiae 71B and Saccharomyces bayanus EC1118, were undertaken to elucidate the differences in their ability to degrade malic acid. Expression of the malic enzyme gene from S. paradoxus RO88 and S. cerevisiae 71B increased towards the end of fermentation once glucose was depleted, whereas no increase in transcription was observed for S. bayanus EC1118 which was also unable to effectively degrade malic acid.

Glucose-inducible expression of rrg1+ in Schizosaccharomyces pombe: post-transcriptional regulation of mRNA stability mediated by the downstream region of the poly(A) site

rrg1+(rapid response to glucose) has been isolated previously as a UV-inducible gene in Schizosaccharomyces pombe, designated as uvi22+. However, it was revealed that the transcript level of this gene was regulated by glucose, not by DNA-damaging agents. Glucose depletion led to a rapid decrease in the level of rrg1+ mRNA, by approximately 50% within 30 min. This effect was readily reversed upon re-introduction of glucose within 1 h. High concentrations (4 and 8%) of glucose showed similar effects on increasing the rrg1+ mRNA level compared with 2% glucose, while a low concentration (0.1%) was not effective in raising the rrg1+ mRNA level. In addition, sucrose and fructose could increase rrg1+ mRNA level. Interestingly, the rapid decline in mRNA level seen upon glucose deprivation resulted from precipitous reduction of mRNA half-life. Serial and internal deletions within the 3'-flanking region of rrg1+ revealed that a 210-nt region downstream of the distal poly(A) site was critical for glucose-regulated expression. Moreover, this downstream region participated in 3'-end formation of mRNA. Taken together, this is the first report on glucose-inducible expression regulated post-transcriptionally by control of mRNA stability in S.pombe.

Malo-ethanolic fermentation in grape must by recombinant strains of Saccharomyces cerevisiae

Recombinant strains of Saccharomyces cerevisiae with the ability to reduce wine acidity could have a significant influence on the future production of quality wines, especially in cool climate regions. L-Malic acid and L-tartaric acid contribute largely to the acid content of grapes and wine. The wine yeast S. cerevisiae is unable to effectively degrade L-malic acid, whereas the fission yeast Schizosaccharomyces pombe efficiently degrades high concentrations of L-malic acid by means of a malo-ethanolic fermentation. However, strains of Sz. pombe are not suitable for vinification due to the production of undesirable off-flavours. Heterologous expression of the Sz. pombe malate permease (mae1) and malic enzyme (mae2) genes on plasmids in S. cerevisiae resulted in a recombinant strain of S. cerevisiae that efficiently degraded up to 8 g/l L-malic acid in synthetic grape must and 6.75 g/l L-malic acid in Chardonnay grape must. Furthermore, a strain of S. cerevisiae containing the mae1 and mae2 genes integrated in the genome efficiently degraded 5 g/l of L-malic acid in synthetic and Chenin Blanc grape musts. Furthermore, the malo-alcoholic strains produced higher levels of ethanol during fermentation, which is important for the production of distilled beverages.

Carbohydrate and energy-yielding metabolism in non-conventional yeasts

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.