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Brettanomyces taxonomy and phylogeny

Over the years, a plethora of different Brettanomy- ces species were suggested and the names of these species were freely used in scientific publications. However, Brettanomyces taxonomy has changed regularly in the past decades and there have been many reclassifications over the years, making direct comparisons between old and more recent papers often challenging. A first attempt to describe the Brettanomyces genus comprehensively was performed by Mathieu Custers in 1940. He defined a classification based on a few asexually reproducing (anamorphic) variants (Custers, 1940; Wijsman et al., 1984). A few decades later, in 1960, the formation of ascospores was observed in some strains and the genus Dekkera was introduced in the taxonomy as the teleomorphic (sexual) counterpart of Bret- tanomyces. In the first edition of their manual on yeast characteristics and identification, Barnett and co-workers described the following 9 Brettanomyces and Dekkera species: Brettanomyces abstinens, Brettanomyces anomalus, Brettanomyces claussenii, Brettanomyces custersianus, Brettanomyces custersii, Brettanomyces lambicus, Brettanomyces naardenensis, Dekkera bruxellensis and Dekkera intermedia (Barnett et al., 1983). Today, five species are formally described, based on molecular analysis of the genera: the anamorphs B. bruxellensis, B. anomalus,

B. custersianus, B. naardenensis, and Brettanomyces nanus, with teleomorphs existing for the first two species, D. bruxellensis and D. anomala. However, according to the recent guidelines of the International Code of Nomenclature for algae, fungi, and plants (the Melbourne Code), fungal species should be assigned only a single valid name. Since the name Brettanomyces is well-known and used more commonly in the food and beverage industries, it will likely be prioritized over Dekkera (Daniel et al., 2014). Moreover, after the first description of spore formation, spores have not been reported again (Schifferdecker et al., 2014), suggesting the teleomorphic state is very rare (see further).

Despite that Brettanomyces spp. have several traits in common with S. cerevisiae, these two genera are genetically only distantly related (Kurtzman and Robnett, 2013). Research papers focusing on the phylogeny of B. bruxellensis and related species remain scarce, but it is shown that Brettanomyces is part of a phylogenetic clade comprising methy- lotrophic yeast species of the genus Ogataea, such as Ogataea angusta, Ogataea glucozyma, Ogataea parapolymorpha, and Ogataea polymorpha, as well as other methylotrophs such as Kuraishia capsu- lata, Candida boidinii, and Komagetaella pastoris (previously Pichia pastoris), although the inclusion of the latter species in this clade is uncertain. This clade seems to have diverged from the ‘CTG- clade' (containing, for example, Candida albicans, Debaryomyces hansenii, and Scheffersomyces stipitis) progenitor after sharing a common ancestor with S. cerevisiae. Using these phylogenetic relationships, it was calculated that B. bruxellensis and S. cerevisiae separated roughly estimated 200 million years ago (Rozp^dowska et al., 2011). Nevertheless, both species share several interesting traits. For example, they have independently acquired resistance to high ethanol concentrations, as well as the ability to produce ethanol even in the presence of oxygen (the Crabtree effect, see earlier section, ‘Natural selection shaped the Saccharomyces genome'), which enables both species to thrive in alcoholic fermentation processes (see further). This is a clear example of parallel evolution, since these traits arose independently in different lineages that share a similar niche (Rozp^dowska et al., 2011).

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