Sulfite plays an important role in beer flavor stability. Although breeding of bottom-fermenting Saccharomyces strains that produce high levels of SO 2 is desirable, it is complicated by the fact that undesirable H 2 S is produced as an intermediate in the same pathway. Here, we report the development of a high-level SO 2 -producing bottom-fermenting yeast strain by integrated metabolome and transcriptome analysis. This analysis revealed that O-acetylhomoserine (OAH) is the rate-limiting factor for the production of SO 2 and H 2 S. Appropriate genetic modifications were then introduced into a prototype strain to increase metabolic fluxes from aspartate to OAH and from sulfate to SO 2 , resulting in high SO 2 and low H 2 S production. Spontaneous mutants of an industrial strain that were resistant to both methionine and threonine analogs were then analyzed for similar metabolic fluxes. One promising mutant produced much higher levels of SO 2 than the parent but produced parental levels of H 2 S.The bottom-fermenting yeast Saccharomyces pastorianus is used to produce beer and has been proposed to be a natural hybrid between Saccharomyces cerevisiae and Saccharomyces bayanus (30). Bottom-fermenting yeasts have two types of genes, one set highly homologous (more than 90% identity) to those of S. cerevisiae and the other less so but highly homologous to S. bayanus (i.e., non-S. cerevisiae [Lg type]) (8,14,27,33). One way in which S. pastorianus differs from baker's yeast (S. cerevisiae) is its tendency to produce higher levels of both sulfite (SO 2 ) and hydrogen sulfide (H 2 S).It is well known that sulfur compounds in beer make significant contributions to flavor and aroma. SO 2 , for example, acts as an antioxidant, which slows the development of oxidation haze and staling of flavors in beer. In contrast, H 2 S has an aroma of rotten eggs and is also a precursor of other compounds with undesirable sensory characteristics. SO 2 and H 2 S are produced by yeast during reductive sulfate assimilation (Fig. 1). Inorganic sulfate is taken up through a sulfate permease and reduced to SO 2 by enzymes encoded by MET3, MET14, and MET16. SO 2 is then reduced to H 2 S by SO 2 reductase encoded by MET5 and MET10 (29). The next intermediate, homocysteine, which is synthesized from H 2 S and O-acetylhomoserine (OAH) by OAH sulfhydrylase encoded by MET17, leads to the formation of cysteine, methionine, and S-adenosylmethionine (SAM). SAM transcriptionally represses all of the genes involved in sulfate assimilation. Park and Bakalinsky previously reported that SSU1 encodes an SO 2 efflux pump that exports intracellular SO 2 through the plasma membrane (18).In the postgenomic era, systematic and high-throughput analyses of mRNA and proteins have become central to recent functional genomics initiatives. Metabolomics entails the analysis of all cellular metabolites and has become a powerful new tool for gaining insight into functional biology. Measurement of numerous metabolites within a cell and tracking concentration changes as a fu...
It has been proposed that bottom-fermenting yeast strains of
The bottom fermenting yeast Saccharomyces pastorianus is reported to have arisen as a natural hybrid of two yeast strains, S. cerevisiae and S. bayanus. The S. pastorianus genome includes S. cerevisiae-type (Sc-type) genes and orthologous lager-fermentingyeast specific-type (Lg-type) genes derived from S. cerevisiae and S. bayanus, respectively. To gain insights into the physiological properties of S. pastorianus, we developed an in situ synthesized 60-mer oligonucleotide microarray for gene expression monitoring of these orthologous genes, consisting of approximately 6600 Sc-type genes and 3200 Lg-type genes. A comparison of the transcriptional profile of orthologous genes (e.g. Sc-type and Lg-type genes) in S. cerevisiae or S. bayanus demonstrated the feasibility of performing gene expression studies with this microarray. Genome-wide analysis of S. pastorianus with this microarray could clearly distinguish more than 67% of the expressed orthologous genes. Furthermore, it was shown that the gene expression of particular Lg-type genes differed from that of the orthologous Sc-type genes, suggesting that some Lg-type and Sc-type genes may have different functional roles. We conclude that the oligonucleotide microarray that we constructed is a powerful tool for the monitoring of gene expression of the orthologous genes of S. pastorianus.
Population preferences for video advertisements vary across short video clips. What underlies these differences? Repeatedly watching a video clip may produce a consistent spatiotemporal pattern of neural activity that is dependent on the individual and the stimulus. Moreover, such consistency may be associated with the degree of engagement and memory of individual viewers. Since the population preferences are associated with the engagement and memory of the individual viewers, the consistency observed in a smaller group of viewers can be a predictor of population preferences. To test the hypothesis, we measured the degree of inter-trial consistency in participants’ electroencephalographic (EEG) responses to repeatedly presented television commercials. We observed consistency in the neural activity patterns across repetitive views and found that the similarity in the spatiotemporal patterns of neural responses while viewing popular television commercials predicts population preferences obtained from a large audience. Moreover, a regression model that used two datasets, including two separate groups of participants viewing different stimulus sets, showed good predictive performance in a leave-one-out cross-validation. These findings suggest that universal spatiotemporal patterns in EEG responses can account for population-level human behaviours.
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