Applied and Environmental Microbiology, April 2002, p. 2018-2025, Vol. 68, No. 4
0099-2240/02/$04.00+0 DOI: 10.1128/AEM.68.4.2018-2025.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
The AWA1 Gene Is Required for the Foam-Forming Phenotype and Cell Surface Hydrophobicity of Sake Yeast
Hitoshi Shimoi,* Kazutoshi Sakamoto, Masaki Okuda, Ratchanee Atthi, Kazuhiro Iwashita, and Kiyoshi Ito
National Research Institute of Brewing, 3-7-1, Kagamiyama, Higashihiroshima 739-0046, Japan
Received 18 October 2001/
Accepted 18 December 2001
Sake, a traditional alcoholic beverage in Japan, is brewed with sake yeasts, which are classified as Saccharomyces cerevisiae. Almost all sake yeasts form a thick foam layer on sake mash during the fermentation process because of their cell surface hydrophobicity, which increases the cells' affinity for bubbles. To reduce the amount of foam, nonfoaming mutants were bred from foaming sake yeasts. Nonfoaming mutants have hydrophilic cell surfaces and no affinity for bubbles. We have cloned a gene from a foam-forming sake yeast that confers foaming ability to a nonfoaming mutant. This gene was named AWA1 and structures of the gene and its product were analyzed. The N- and C-terminal regions of Awa1p have the characteristic sequences of a glycosylphosphatidylinositol anchor protein. The entire protein is rich in serine and threonine residues and has a lot of repetitive sequences. These results suggest that Awa1p is localized in the cell wall. This was confirmed by immunofluorescence microscopy and Western blotting analysis using hemagglutinin-tagged Awa1p. Moreover, an awa1 disruptant of sake yeast was hydrophilic and showed a nonfoaming phenotype in sake mash. We conclude that Awa1p is a cell wall protein and is required for the foam-forming phenotype and the cell surface hydrophobicity of sake yeast.
* Corresponding author. Mailing address: National Research Institute of Brewing, 7-3-1 Kagamiyama, Higashihiroshima 739-0046, Japan. Phone: 81-824-20-0826. Fax: 81-824-20-0809. E-mail: simoi{at}nrib.go.jp.
Applied and Environmental Microbiology, April 2002, p. 2018-2025, Vol. 68, No. 4
0099-2240/02/$04.00+0 DOI: 10.1128/AEM.68.4.2018-2025.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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Copyright © 2002 by the American Society for Microbiology. All rights reserved.