Academic journal article Genetics

Molecular-Genetic Biodiversity in a Natural Population of the Yeast Saccharomyces Cerevisiae from "Evolution Canyon": Microsatellite Polymorphism, Ploidy and Controversial Sexual Status

Academic journal article Genetics

Molecular-Genetic Biodiversity in a Natural Population of the Yeast Saccharomyces Cerevisiae from "Evolution Canyon": Microsatellite Polymorphism, Ploidy and Controversial Sexual Status

Article excerpt

ABSTRACT

The yeast S. cerevisiae is a central model organism in eukaryotic cell studies and a major component in many food and biotechnological industrial processes. However, the wide knowledge regarding genetics and molecular biology of S. cerevisiae is based on an extremely narrow range of strains. Studies of natural populations of S. cerevisiae, not associated with human activities or industrial fermentation environments, are very few. We isolated a panel of S. cerevisiae strains from a natural microsite, "Evolution Canyon" at Mount Carmel, Israel, and studied their genomic biodiversity. Analysis of 19 microsatellite loci revealed high allelic diversity and variation in ploidy level across the panel, from diploids to tetraploids, confirmed by flow cytometry. No significant differences were found in the level of microsatellite variation between strains derived from the major localities or microniches, whereas strains of different ploidy showed low similarity in allele content. Maximum genetic diversity was observed among diploids and minimum among triploids. Phylogenetic analysis revealed clonal, rather than sexual, structure of the triploid and tetraploid subpopulations. Viability tests in tetrad analysis also suggest that clonal reproduction may predominate in the polyploid subpopulations.

(ProQuest Information and Learning: ... denotes formulae omitted.)

THE budding yeast Saccharomyces cerevisiae is one of the central model organisms of eukaryotic cell studies (DICKINSON 2000). The wide knowledge about the genetic and molecular biology of the yeast S. cerevisiae has accumulated on an extremely narrow range of genotypes selected due to their specific technological features or suitability to laboratory conditions and, hence, hardly representing the species (LIU et al. 1996; MORTIMER 2000).

The yeast S. cerevisiae is also a central component of many important industrial processes, including baking, brewing, distilling, and wine making. Once again, in this domain, most studies have included selected, commercially available yeast strains removed from the natural adaptation and evolution processes. Relatively limited genetic work has been done on commercial baking, wine, and brewing strains. In the last decade, some studies dealt with isolates from nature, wineries, and grapes (SANGORRIN et al. 2001; VAN DER AA et al. 2001; FAY and BENAVIDES 2005), as well as from contaminants of different lager breweries (VAN DER AA and JESPERSEN 1998; JESPERSEN et al. 2000). In fact, cells of S. cerevisiae are rarely isolated from natural grape surfaces except damaged grapes (VAUGHAN-MARTINI and MARTINI 1995; MARTINI et al. 1996; MORTIMER and POLSINELLI 1999), suggesting that insects such as bees or Drosophila are vectors for spreading of this microorganism (STEVIC 1962; SNOWDON and CLIVER 1996; MORTIMER and POLSINELLI 1999).

MORTIMER (2000) reported that attempts to find S. cerevisiae in regions remote from human activities have been unsuccessful. A model proposed by NAUMOV (1996) states that S. cerevisiae strains in European soil originate from human activity, i.e., are found only in association with human civilization, especially in winery environments. On the other hand, S. cerevisiae was also found in exudates from North American oaks (NAUMOV et al. 1998). The foregoing evidence calls for extended population-genetic (ZEYL 2000) and molecular-genetic studies of yeast in nature (LITI and LOUIS 2005).

The yeast S. cerevisiae can exist in a vegetative mode in haploid, diploid, and higher ploidy states. Haploid cells of S. cerevisiae exhibit one of two phenotypes: mating types a or α. Correspondingly, diploid and polyploid cells can exhibit one of three mating phenotypes: a, α, or a/α. When cells of opposite mating types meet they participate in a mating process that results in cell and nuclear fusion to create an a/α-zygote. a/α-cells can either reproduce by mitosis or undergo meiosis and sporulation, with a further possibility of a x α gamete fusion. …

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