Identification of bottom-fermenting yeast genes expressed during lager beer fermentation

It has been proposed that bottom-fermenting yeast strains of Saccharomyces pastorianus possess at least two types of genomes. Sequences of genes of one genome [S. cerevisiae (Sc)-type] have been found to be highly homologous (more than 90% identity) to S. cerevisiae S288C sequences, while those of the other [Lager (Lg)-type] are less so. To identify and discriminate Lg-type from Sc-type genes expressed during lager beer fermentation, normalized cDNA libraries were constructed and analysed. From approximately 22 000 ESTs, 3892 Sc-type and 2695 Lg-type ORFs were identified. Expression patterns of Sc- and Lg-type genes did not correlate with particular cell functions in KEGG classification system. Moreover, 405 independent clones were isolated that have no significant homology with sequences in the S288C database, suggesting that they include the bottom-fermenting yeast-specific (BFY) genes. Most of BFY genes have significant homology with the S. bayanus genome. The DNA sequences of S. pastorianus non-Sc-type ORFs were submitted to DDBJ/ GenBank/EMBL under Accession Nos CJ992285-CJ998763.