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L. Strack and U. Stahl

"Omics" technologies comprise genomics, transcriptomics, proteomics and metabolomics; the last three fields are pooled within the notion "functional genomics". In this review, these techniques which concentrate on aspects of the "course from gene to metabolites" nare surveyed especially with regard to bottom-fermenting brewer's yeasts. ith the aid of these global methods it is possible to combine a collective knowledge of an investigated organism which is necessary to understand the details of its metabolic system. Hence, the challenge is to introduce the above mentioned studies for the determination of targets and approaches for the improvement of yeast organisms. Herein, brewing yeasts are reviewed with concern to the determination of their "ome" levels. But because of the hybrid nature of the brewer's yeast's genome problems emerged regarding the "omics"-applicability which are depicted in this paper furthermore.This Minireview is the first section of a two-part publication. The second part with the title "Reduction of diacetyl production by brewer's yeast" will be published in the next issue of Brewing Science in February 2010. Yeasts have been used over centuries for the production of wines, bakery products and beer. But the fact that microorganisms such as yeasts are responsible for the fermentation and by-product formation has only been known for about 150 years. Today, these yeasts are used precisely. Especially for the beer production the selection of adequate yeasts is necessary to guarantee an optimal brewing process and taste of the beverage. In general, two types of beer can be classified: ale beers using top-fermenting yeasts and lager brews using bottom-fermenting yeasts which each require different fermentation conditions and as a consequence, show a diverse product character. But various yeast species do not combine every desired trait in one strain and therefore, these yeasts still need to be optimised. Hence, for the brewing industry it is indispensable that yeast improvement is the main focus of research purposes. But due to the fact that over 90 % of the worldwide produced beer are lager brews the research concentrates on lager brewing yeasts [1]. Brewer's yeasts of the Saccharomyces sensu stricto group differ from Saccharomyces cerevisiae regarding their genomes. Specifically, the size of the lager brewer's yeast?s genome is approximately twice the size of S. cerevisiae and therefore reflects that lager brewer?s yeasts vary from other brewing yeasts [1, 2]. Their genome is a combination of at least two species of which one was clearly identified as S. cerevisiae. The other ancestors were considered to be derived from another Saccharomyces species [1, 3]. Older results hypothesised that brewer's yeast is a hybrid of S. cerevisiae and S. monacensis or S. bayanus [4-6]. However, subtelomeric sequence hybridisation has suggested that S. monacensis is likely to be a closely related hybrid to brewer's yeast, rather than an ancestor [3]. Earlier, outcomes argued for Saccharomyces uvarum and/or Saccharomyces bayanus so that the lager brewer's yeast's genome could have been composed of three different ancestors. Furthermore, there were findings that lager yeasts consist either of the pure lines S. uvarum or S. bayanus or they are combinations together with S. cerevisiae. In addition, there could be a fourth part which may also originate from S. uvarum and was named "lager" according to its first revelation from lager brewer's yeast [7]. Moreover, Gonzalez et al. [8] and Naumova et al. [9] postulated new hybrids consisting of S. cerevisiae and other yeasts of the Saccharomyces sensu stricto group like S. kudriavzevii which constitute to the diversity and complexity of brewer's yeasts. But still it is unclear whether these hybrids are "real" species or may be only breedings of the same species. Recently, one widely used strain (W34/70) had been fully sequenced in order to finally clarify the origin of the brewer's yeasts. The outcome was brewer's yeast being a hybrid of S. cerevisiae and S. bayanus with two sub-genomes and a S. bayanus-based mitochondrial genome thus giving the possibility for the application of new technologies and basic research [10]. The type strains of bottom fermenting brewer's yeast have formerly been named S. carlsbergensis or S. monacensis but now the hybrid genome lines which contain a S. cerevisiae genome part should be named S. pastorianus [7].

Descriptors: brewer's yeast, hybrid genome, omics technologies, genetics

BrewingScience - Monatsschrift fr Brauwissenschaft, 62 (November/December 2009), pp. 187-190