HUU VANG NGUYEN (1), Lucie Hazelwood (2), Mustapha Nedjma (3)
(1) INRA, AgroParisTech, Thiverval-Grignon, France; (2) NIZO Food Research BV, Netherlands; (3) nedjman@aol.com
For yeast taxonomists, Saccharomyces pastorianus (name given by A. Vaughan-Martini to honor L. Pasteur), including S. carlsbergensis, is the species name of brewing lager yeasts. This species was regarded as a hybrid of S. cerevisiae and S. bayanus by DNA/DNA reassociation. Saccharomyces bayanus (Saccardo, 1895), was recognized as a true species while S. uvarum (Beijerinck, 1898) has been reclassified as a synonym of S. bayanus. However, S. carlsbergensis (Hansen) and S. uvarum (Beijerinck)
have been thought to be conspecific. The persistence of confusing the
names of the species was highlighted in prior literature or, more
recently, in studies that do not rely on the reclassification proposed
by Vaughan-Martini and Kurtzman in 1985 (Stewart and Russel, 1983;
Hinchliffe and Vakeria, 1989). Researchers are thus faced with a
situation in which three yeast species are tightly linked by their given
names, resulting in a name being used for two species. In an attempt to
clarify this situation, we established the karyotypes of S. uvarum strains and compared them with those of S. carlsbergensis and S. monacensis. Indeed, they exhibited two distinct groups of karyotypes. The main reason for the confusion of S. carlsbergensis/uvarum was that S. carlsbergensis and S. uvarum are both cryophilic, expressing the capacity to degrade melibiose by melibiase activity and encoding by the MEL1 gene, which has been cloned and sequenced in S. carlsbergensis. To date, MEL1 is thought to originate from S. uvarum. With the availability of the genome of S. uvarum strain CBS7001, we selected primers to amplify and sequence the MEL1 gene from several S. uvarum strains, which resulted in the SuMEL1 nucleotide sequence. This one shares only 78% identity with the MEL1 gene from S. carlsbergensis as well as three S. cerevisiae Mel+ strains: ATCC42367, CBS2354, and UWOPS03-461.4. We thus concluded that S. carlsbergensis carried the ScMEL1 gene and not the SuMEL1. Consequently, based on karyotype and MEL1 sequence criteria, S. carlsbergensis is different from S. uvarum. In our previous studies, S. bayanus itself revealed to be a hybrid S. cerevisiae × S. uvarum; thus, we reinstated S. uvarum (Beijerinck) as a bona fide species. In the same study, we showed that S. carlsbergensis carries sequences mainly from S. cerevisiae and some sequences derived from S. uvarum with multiple neutral nucleotide polymorphism (MNNP) qualified by many authors as lager sequences. Conclusion: S. pastorianus is actually an S. cerevisiae × S. uvarum hybrid. S. carlsbergensis (S. pastorianus) is no longer a synonym of S. uvarum. The impact of melibiose was measured in experimental brewing with strains Mel+.
Huu Vang Nguyen was born in 1946 and obtained a Ph.D. degree from the
University of Bruxelles, Belgium in 1976. Huu Vang was an assistant
professor, biochemistry, at the University of Poitier, France
(1977–1983); baker’s yeast producer at R&D Lesaffre Company
(1984–1990); and public researcher with INRA (Institut National de la
Recherche Agronomique), France (1991–2009), curator of the yeast
Collection de Levures d’Intérêt Biotechnologique (CLIB), molecular
taxonomy of yeasts (2009–present): micalis (Microbiologie de
l’Alimentation au Service de la Santé), and genomics and classification
of yeasts.
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