Previous Article | Next Article 
Applied and Environmental Microbiology, August 2007, p. 5363-5369, Vol. 73, No. 16
0099-2240/07/$08.00+0 doi:10.1128/AEM.01029-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
Saccharomyces cerevisiae Signature Genes for Predicting Nitrogen Deficiency during Alcoholic Fermentation
,
A. Mendes-Ferreira,1,2
M. del Olmo,2
J. García-Martínez,3
E. Jiménez-Martí,2
C. Leão,4
A. Mendes-Faia,1* and
J. E. Pérez-Ortín2,3
Centro de Genética e Biotecnologia-IBB, Universidade de Trás-os-Montes e Alto Douro, Vila Real, Portugal,1
Departament de Bioquímica i Biologia Molecular, Universitat de València, València, Spain,2
Sección de Chips de DNA, Universitat de València, València, Spain,3
Instituto de Investigação em Ciências da Vida e Saúde (ICVS), Escola de Ciências da Saúde, Universidade do Minho, Braga, Portugal4
Received 9 May 2007/
Accepted 20 June 2007

ABSTRACT
Genome-wide analysis of the wine yeast strain
Saccharomyces cerevisiae PYCC4072 identified 36 genes highly expressed under
conditions of low or absent nitrogen in comparison with a nitrogen-replete
condition. Reverse transcription-PCR analysis for four of these
transcripts with this strain and its validation with another
wine yeast strain underlines the usefulness of these signature
genes for predicting nitrogen deficiency and therefore the diagnosis
of wine stuck/sluggish fermentations.

INTRODUCTION
Nitrogen deficiency has been associated with major problems
encountered in contemporary wine making, especially those related
to slow (sluggish) and incomplete (stuck) fermentations (
2,
3,
10,
11,
19). Under wine-making conditions, initial low levels
of nitrogen act by limiting growth and biomass, resulting in
a reduced fermentation rate (
14,
23). Until completing alcoholic
fermentation, the fermenting juice is at risk of spoilage due
to oxidation and microbial activity, which can reduce the quality
and thus the commercial value of the final product. A few systematic
studies have been done to identify changes in gene expression
that take place in response to nitrogen deficiency under enological
conditions. From these studies, some genes, such as
CAR1 (
5)
and
ACA1 (
9), were indicated as being more strongly expressed
with nitrogen limitation.
Genome-wide expression analysis has also emerged as a powerful tool that can be used for identification of signature genes that behave in a similar fashion at a particular time point or under particular conditions (13). It has been successfully used in the identification of predictive biomarkers for clinical diagnosis (17, 20, 22). An analogous approach has been recently used with Saccharomyces cerevisiae for identifying CO2-responsive genes (1) and macronutrient (4, 21) and micronutrient (8) limitation under laboratory growth conditions. In a previous study, we used a genome-wide approach integrating the different situations of nitrogen supply: (i) with enough nitrogen to complete sugar fermentation, (ii) with nitrogen-limiting fermentation, and (iii) with addition of nitrogen to the nitrogen-deficient fermentation (15). In our previous study (15), samples for DNA macroarrays were taken from 11 points corresponding to different stages of the three fermentations, combining low and/or high concentrations of glucose, nitrogen, and ethanol (Table 1). The public data set, submitted to the GEO data repository (http://www.ncbi.nlm.nih.gov/geo/) under accession number GSE5842 (15), contains hybridization values for all time point replicates. Normalized final values are available from our website (http://scsie.uv.es/chipsdna/).
View this table:
[in this window]
[in a new window]
|
TABLE 1. Fermentation parameters evaluated during experiments carried out with synthetic grape juice medium with 20% glucose and different initial nitrogen concentrationsa
|
In the present study, the main goal was to identify genes that
showed robust changes in their expression levels specifically
associated with nitrogen deficiency and that could be potential
candidates as biomarkers for predicting sluggish or stuck fermentations.
For this purpose we used the DNA macroarray data obtained with
the wine yeast strain
S. cerevisiae PYCC4072 and compared gene
expression levels between the nitrogen-replete condition and
various defined situations of low nitrogen and N starvation,
irrespective of the glucose availability, ethanol production,
or other variations than can occur during vinification. Based
on the data presented in Table
1, two time points, CF48 (control
fermentation at 48 h) and LN24 (low-nitrogen fermentation at
24 h), were selected for the low-nitrogen conditions and five
time points, CF96, LN48, LN80, LN96, and LN144, were chosen
for the N starvation conditions. Pairwise comparisons were done
using sample CF24 as the reference, since at that stage nitrogen
was still abundant (178 mg liter
–1). To estimate significantly
differentially expressed genes in pairwise comparisons, a z-test
was applied, and false-discovery-rate analysis was the method
used for false-positive error correction.
To select genes that displayed a consistent change in expression in the different nitrogen situations, the expression profiles were filtered as schematically presented in Fig. 1. First, only those genes with signal values in all time points selected above were considered (5,134 genes). Second, two selection criteria were cumulatively applied: the expression level had to change (i) significantly (P < 0.05) and (ii) by at least threefold compared to that of the reference sample under low-nitrogen and/or N starvation conditions. Genes displaying opposite changes in expression behavior within each of the two conditions were discarded. Genes were grouped into three sets: (i) those with significant changes at both time points only with a low extracellular nitrogen level (LN24 and CF48) (low-nitrogen response); (ii) those that showed significant changes in expression only between CF96, LN48, LN80, LN96, and LN144 and the reference cultures (CF24) (N starvation response); and (iii) those that displayed significant changes in expression under both low-nitrogen and N starvation conditions (common response).
Sixty-five genes were identified that specifically changed in
response to low nitrogen, and all were up-regulated (see Fig.
S1 in the supplemental material), while 61 genes were specifically
reset in response to nitrogen starvation. In this last set,
only
CUP1-2, involved in resistance to high concentrations of
copper, had higher expression under the nitrogen-deprived conditions
(see Fig. S1 in the supplemental material). Indeed, this gene
has already been reported to be one of the highly expressed
genes in the late stationary phase during alcoholic fermentation
(
24). A total of 390 genes were found to be significantly affected
under both low-nitrogen and N starvation conditions. Among those
genes, 72 genes had consistently higher expression (see Table
S2 in the supplemental material) while 318 had lower expression
(see Table S3 in the supplemental material) under all nitrogen
deprivation conditions relative to the reference situation.
Results for these genes were compared with those for the
environmental
stress
response (ESR) family genes obtained by evaluating the
transcriptional responses with a wide range of stress stimuli,
including nitrogen depletion (
6). It was found that 27 of the
72 up-regulated genes (
P value, 1
x 10
–18) and 128 of
the 318 down-regulated genes (
P value, 3
x 10
–53) are
among the ESR genes, indicating that the yeast cell response
to nitrogen restriction under vinification conditions involves
the ESR.
To identify potential candidate biomarker genes for predicting nitrogen shortage during alcoholic fermentation, analyses were restricted to the 72 up-regulated genes, and their responses were examined after nitrogen refeeding. Only those genes whose expression decreased by at least twofold after nitrogen addition (RF80 [refed fermentation at 80 h]/LN48) and increased again at least threefold when nitrogen became depleted (RF96/RF80 and RF144/RF80) were considered. Thirty-six genes passed all rather stringent criteria applied, suggesting that they could be promising candidates for predicting nitrogen deficiency during alcoholic fermentation (Table 2). The remaining genes could be involved in nonspecific responses to nitrogen limitation and associated with a more general response, namely, those responding to other intracellular and/or environmental changes that occur under nitrogen deficiency conditions. Further research is required to clarify this aspect. Several interesting aspects of this set of candidate genes should be highlighted (Table 2). Half of these genes have been identified as being ESR upregulated (6), and thus, their usefulness for the specific diagnosis of the nitrogen deficiency response could be limited. A large number of genes (50%) have no known molecular function. Determining their physiological role could give further insights into their contributions to the yeast response to nitrogen deficiency. Twelve genes are among the 127 genes induced in cells in stationary-phase cultures (P value, 3 x 10–12). Two of them, HBT1 and FMP45, are considered essential for long-term survival in stationary phase (12). Genes whose expression is known to be under glucose repression, such as IDP2, XYL2, and the transcription factor CAT8, involved in the derepression of a number of genes during the diauxic shift (7), are part of this restricted group of genes, despite the high glucose levels present at all time points. Furthermore, 14 genes of our signature group were found to be specifically more highly expressed under carbon limitation (4, 21). This result supports the previous suggestion that the yeast cell responses to nitrogen limitation/starvation observed in this study have similarities to the yeast cell response to glucose limitation (15). In addition, two other transcription factors, XBP1, whose transcriptional activation has been considered a key response of yeast cells to nitrogen limitation (16), and CUP2, involved in copper-responsive transcriptional regulation of the metallothionein genes CUP1-1 and CUP1-2, are part of the candidate genes identified in the current study. The high mRNA levels of CUP1-2 observed under N starvation indicate that maintenance of copper homeostasis in yeast cells could be decisive for yeast cell survival under such conditions. Experimental identification of the set of genes that are regulated by each one of these transcription factors, either by transcriptional profiling of knockout mutants or by overexpression of the various factors, will be necessary to access their functions in the regulation of nitrogen availability responses. Finally, seven of the proposed candidate genes (P value, 1 x 10–8) were formerly included in the top 50 open reading frames induced by ammonium starvation (26). The finding of an overlap between the current set of data, corresponding to a wine yeast strain grown under batch fermentation conditions, and that from Wu et al. (26), obtained with a laboratory S. cerevisiae strain in chemostat cultures, supports the accuracy of the approach considered herein. Despite the overlap shown in Table 2, it is worth mentioning that this study introduced seven genes for which no previous relationship had been established with ESR (6), ammonium starvation (26), nitrogen and carbon limitation (4, 21), or stationary phase (12) but which are induced under all of the conditions of nitrogen limitation and starvation considered in this work.
View this table:
[in this window]
[in a new window]
|
TABLE 2. Thirty-six signature genes identified in this work as potential candidates for predicting nitrogen deficiency under wine-making conditions and their overlapping with other reported conditionsa
|
In order to validate the differential expression of candidate
genes obtained by macroarray analysis, semiquantitative reverse
transcription-PCR (RT-PCR) was performed using the same RNA
from the original experiments with
S. cerevisiae PYCC4072 according
to the protocol described by Zuzuarregui et al. (
27). Table
3 includes the sequences of the oligonucleotides used in these
amplification reactions, the number of cycles, and the hybridization
temperature. The
PDA1 gene was used for normalization of the
data, since it shows a constitutive expression in batch and
chemostat cultures in the presence of various carbon sources
(
25). Four up-regulated genes (
MSC1,
XYL2,
RTN2, and
ODC1) were
selected from the candidate gene list for this purpose (Fig.
2). The expression levels of
RTN2 and
ODC1 in both RT-PCR and
macroarray analysis showed an increase under nitrogen limitation
and especially starvation. Also, for the
MSC1 and
XYL2 genes,
the pattern obtained by RT-PCR supported the macroarray results;
the mRNA levels were almost undetectable in the reference sample
(CF24), and the highest mRNA abundance was shown at time LN80,
under starvation conditions, decreasing after nitrogen addition
to a greater degree in the case of
XYL2. RTN2 and
MSC1 have
been described as part of the ESR (
6). On the other hand, these
two genes together with
ODC1 were included in the top 50 open
reading frames induced by ammonium starvation in
S. cerevisiae grown in chemostat culture (
21). The validation of these genes
reinforces the consistency of the results obtained in this study
and shows that some relationship can be found between growth
under vinification and laboratory conditions. Besides, this
analysis allows the addition of several genes, including
XYL2,
to the list of those previously proposed to be induced by nitrogen
deficiency (
4,
21).
To assess whether the results obtained for the wine yeast strain
S. cerevisiae PYCC4072 could be extrapolated to other wine strains
and other fermentation conditions, we studied the transcriptional
response of the same four genes with another commercial wine
yeast strain. The experiments using
S. cerevisiae strain ICV16
(Fermicru primeur, DSM) were performed with synthetic grape
juice (
18) containing 300 mg liter
–1 (MS300) or 60 mg
liter
–1 (MS60) of assimilable nitrogen as a mixture of
ammonium and amino acids in a proportion of 2:3, respectively,
following the experimental details described by Jiménez-Martí
et al. (
9). Nitrogen was added (240 mg liter
–1 of ammonium)
to the MS60 experiment 72 h after inoculation, when total assimilable
nitrogen was almost completely consumed (5.25 mg liter
–1 of nitrogen remained in the extracellular medium at this time
point). In these experiments, active dry yeasts were rehydrated
in water according to the manufacturer's instructions and used
for inoculation to a final count of 5
x 10
6 cells ml
–1,
as determined by total cell counts. The results shown in Fig.
3 further confirmed that the selected genes are also applicable
to other wine strains irrespective of growth medium composition
and fermentation conditions.
It is worth mentioning that in order to get a reasonable number
of marker genes for this signature group, we have focused only
on those with higher levels of expression under nitrogen deficiency
conditions. A similar approach could be followed for the down-regulated
genes. The presence in this group of several
MET genes, essential
for the assimilatory reduction pathway of sulfate to sulfide,
is of great interest, and further studies are being carried
out to understand their relevance in the wine-making process.
A designed DNA chip incorporating some of the genes identified in this study can be developed to assist the winemaker in assessing the nitrogen status of the fermenting grape juice. The ultimate goal is that such a chip can be used to predict premature fermentation arrest due to a nitrogen shortage and to customize treatment strategies. Nevertheless, it should be emphasized that these observations must be viewed as preliminary, and expansion to other yeast strains is required before a specialized DNA chip for predictive diagnosis of this problem can be designed.

ACKNOWLEDGMENTS
This work was carried out in the framework of project PTDC/AGR-ALI/71460/2006
(grant to A.M.-F.). This work was also supported by grants AGL2005-00508
and BMC2003-07072-C03-02 from the Spanish Ministerio de Educación
y Ciencia to M.O. and to J.E.P.-O., respectively. Elena Jiménez-Martí
is an FPI Fellow for the Spanish Government.
We thank R. N. Bennett for English revision of the manuscript.

FOOTNOTES
* Corresponding author. Mailing address: Centro de Genética e Biotecnologia-IBB, Universidade de Trás-os-Montes e Alto Douro, Vila Real, Portugal. Phone: 351 259350554. Fax: 351 259350480. E-mail:
afaia{at}utad.pt 
Published ahead of print on 29 June 2007. 
Supplemental material for this article may be found at http://aem.asm.org/. 

REFERENCES
1 - Aguilera, J., T. Petit, J. H. de Winde, and J. T. Pronk. 2005. Physiological and genome-wide transcriptional responses of Saccharomyces cerevisiae to high carbon dioxide concentrations. FEMS Yeast Res. 5:579-593.[CrossRef][Medline]
2 - Bisson, L. F. 1991. Influence of nitrogen on yeast and fermentation of grapes, p. 78-89. In J. M. Rantz (ed.), Proceedings of the International Symposium on Nitrogen in Grapes and Wine. American Society for Enology and Viticulture, Davis, CA.
3 - Bisson, L. F. 1999. Stuck and sluggish fermentations. Am. J. Enol. Vitic. 50:107-119.[Abstract/Free Full Text]
4 - Boer, V. M., J. H. de Winde, J. T. Pronk, and M. D. Piper. 2003. The genome-wide transcriptional responses of Saccharomyces cerevisiae grown on glucose in aerobic chemostat cultures limited for carbon, nitrogen, phosphorus, or sulfur. J. Biol. Chem. 278:3265-3274.[Abstract/Free Full Text]
5 - Carrasco, P., J. E. Pérez-Ortín, and M. del Olmo. 2003. Arginase activity is a useful marker of nitrogen limitation during alcoholic fermentations. Syst. Appl. Microbiol. 26:471-479.[CrossRef][Medline]
6 - Gasch, A. P., P. T. Spellman, C. M. Kao, O. Carmel-Harel, M. B. Eisen, G. Storz, D. Botstein, and P. O. Brown. 2000. Genomic expression programs in the response of yeast cells to environmental changes. Mol. Biol. Cell 11:4241-4257.[Abstract/Free Full Text]
7 - Hedges, D., M. Proft, and K. D. Entian. 1995. CAT8, a new zinc cluster-encoding gene necessary for derepression of gluconeogenic enzymes in the yeast Saccharomyces cerevisiae. Mol. Cell. Biol. 15:1915-1922.[Abstract]
8 - Higgins, V. J., P. J. Rogers, and I. W. Dawes. 2003. Application of genome-wide expression analysis to identify molecular markers useful in monitoring industrial fermentations. Appl. Environ. Microbiol. 69:7535-7540.[Abstract/Free Full Text]
9 - Jiménez-Martí, E., A. Aranda, A. Mendes-Ferreira, A. Mendes-Faia, and M. del Olmo. 2007. The nature of the nitrogen source added to nitrogen depleted vinifications conducted by a Saccharomyces cerevisiae strain in synthetic must affects gene expression and the levels of several volatile compounds. Antonie Leeuwenhoek 92:61-75.[CrossRef][Medline]
10 - Kunkee, R. E. 1991. Relationship between nitrogen content in must and sluggish fermentation, p. 148-155. In J. M. Rantz (ed.), Proceedings of the International Symposium on Nitrogen in Grapes and Wine. American Society for Enology and Viticulture, Davis, CA.
11 - Manginot, C., J. L. Roustan, and J. M. Sablayrolles. 1998. Nitrogen demand of different yeast strains during alcoholic fermentation. Importance of the stationary phase. Enzyme Microb. Technol. 23:511-517.[CrossRef]
12 - Martinez, M. J., S. Roy, A. B. Archuletta, P. D. Wentzell, S. S. Anna-Arriola, A. L. Rodriguez, A. D. Aragon, G. A. Quinones, C. Allen, and M. Werner-Washburne. 2004. Genomic analysis of stationary-phase and exit in Saccharomyces cerevisiae: gene expression and identification of novel essential genes. Mol. Biol. Cell 15:5295-5305.[Abstract/Free Full Text]
13 - Martoglio, A. M., J. W. Miskin, S. K. Smith, and D. J. MacKay. 2002. A decomposition model to track gene expression signatures: preview on observer-independent classification of ovarian cancer. Bioinformatics 18:1617-1624.[Abstract/Free Full Text]
14 - Mendes-Ferreira, A., A. Mendes-Faia, and C. Leão. 2004. Growth and fermentation patterns of Saccharomyces cerevisiae under different ammonium concentrations and its implications in winemaking industry. J. Appl. Microbiol. 97:540-545.[CrossRef][Medline]
15 - Mendes-Ferreira, A., M. del Olmo, J. Garcia-Martinez, E. Jiménez-Martí, A. Mendes-Faia, J. Perez-Ortin, and C. Leão. 2007. Transcriptional response of Saccharomyces cerevisiae to different nitrogen concentrations during alcoholic fermentation. Appl. Environ. Microbiol. 73:3049-3060.[Abstract/Free Full Text]
16 - Miled, C., C. Mann, and G. Faye. 2001. Xbp1-mediated repression of CLB gene expression contributes to the modifications of yeast cell morphology and cell cycle seen during nitrogen-limited growth. Mol. Cell. Biol. 21:3714-3724.[Abstract/Free Full Text]
17 - Modena, P., E. Lualdi, F. Facchinetti, J. Veltman, J. F. Reid, S. Minardi, I. Janssen, F. Giangaspero, M. Forni, G. Finocchiaro, L. Genitori, F. Giordano, R. Riccardi, E. F. Schoenmakers, M. Massimino, and G. Sozzi. 2006. Identification of tumor-specific molecular signatures in intracranial ependymoma and association with clinical characteristics. J. Clin. Oncol. 24:5223-5233.[Abstract/Free Full Text]
18 - Riou, C., J. M. Nicaud, P. Barre, and C. Gaillardin. 1997. Stationary-phase gene expression in Saccharomyces cerevisiae during wine fermentation. Yeast 13:903-915.[CrossRef][Medline]
19 - Salmon, J. M. 1989. Effect of sugar transportation inactivation in Saccharomyces cerevisiae on sluggish and stuck enological fermentations. Appl. Environ. Microbiol. 55:953-958.[Abstract/Free Full Text]
20 - Sorlie, T., C. M. Perou, R. Tibshirani, T. Aas, S. Geisler, H. Johnsen, T. Hastie, M. B. Eisen, M. van de Rijn, S. S. Jeffrey, T. Thorsen, H. Quist, J. C. Matese, P. O. Brown, D. Botstein, P. Eystein Lonning, and A. L. Borresen-Dale. 2001. Gene expression patterns of breast carcinomas distinguish tumor subclasses with clinical implications. Proc. Natl. Acad. Sci. USA 98:10869-10874.[Abstract/Free Full Text]
21 - Tai, S. L., V. M. Boer, P. Daran-Lapujade, M. C. Walsh, J. H. de Winde, J. M. Daran, and J. T. Pronk. 2005. Two-dimensional transcriptome analysis in chemostat cultures. Combinatorial effects of oxygen availability and macronutrient limitation in Saccharomyces cerevisiae. J. Biol. Chem. 280:437-447.[Abstract/Free Full Text]
22 - van de Vijver, M., Y. He, L. van't Veer, H. Dai, A. Hart, D. Voskuil, G. Schreiber, J. Peterse, C. Roberts, M. Marton, M. Parrish, D. Atsma, A. Witteveen, A. Glas, L. Delahaye, T. van der Velde, H. Bartelink, S. Rodenhuis, E. Rutgers, S. Friend, and R. Bernards. 2002. A gene-expression signature as a predictor of survival in breast cancer. N. Engl. J. Med. 347:1999-2009.[Abstract/Free Full Text]
23 - Varela, C., F. Pizarro, and E. Agosin. 2004. Biomass content governs fermentation rate in nitrogen-deficient wine musts. Appl. Environ. Microbiol. 70:3392-3400.[Abstract/Free Full Text]
24 - Varela, C., J. Cárdenas, F. Melo, and E. Agosin. 2005. Quantitative analysis of wine yeast gene expression profiles under winemaking conditions. Yeast 22:369-383.[CrossRef][Medline]
25 - Wenzel, T. J., M. A. Luttik, J. A. van den Berg, and H. Y. de Steensma. 1993. Regulation of the PDA1 gene encoding the E1 alpha subunit of the pyruvate dehydrogenase complex from Saccharomyces cerevisiae. Eur. J. Biochem. 218:405-411.[Medline]
26 - Wu, J., N. Zhang, A. Hayes, K. Panoutsopoulou, and S. G. Oliver. 2004. Global analysis of nutrient control of gene expression in Saccharomyces cerevisiae during growth and starvation. Proc. Natl. Acad. Sci. USA 101:3148-3153.[Abstract/Free Full Text]
27 - Zuzuarregui, A., L. Monteoliva, C. Gil, and M. del Olmo. 2006. Transcriptomic and proteomic approach for understanding the molecular basis of adaptation of Saccharomyces cerevisiae to wine fermentation. Appl. Environ. Microbiol. 72:836-847.[Abstract/Free Full Text]
Applied and Environmental Microbiology, August 2007, p. 5363-5369, Vol. 73, No. 16
0099-2240/07/$08.00+0 doi:10.1128/AEM.01029-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.