Schizosaccharomyces pombe, also called "fission yeast", is a species of yeast used in traditional brewing and as a model organism in molecular and cell biology. It is a unicellular eukaryote, whose cells are rod-shaped. Cells typically measure 3 to 4 micrometres in diameter and 7 to 14 micrometres in length. Its genome, which is approximately 14.1 million base pairs, is estimated to contain 4,970 protein-coding genes and at least 450 non-coding RNAs. These cells maintain their shape by growing exclusively through the cell tips and divide by medial fission to produce two daughter cells of equal size, which makes them a powerful tool in cell cycle research. Fission yeast was isolated in 1893 by Paul Lindner from East African millet beer. The species name pombe is the Swahili word for beer. It was first developed as an experimental model in the 1950s: by Urs Leupold for studying genetics, and by Murdoch Mitchison for studying the cell cycle. Paul Nurse, a fission yeast researcher, successfully merged the independent schools of fission yeast genetics and cell cycle research. Together with Lee Hartwell and Tim Hunt, Nurse won the 2001 Nobel Prize in Physiology or Medicine for work on cell cycle regulation. The sequence of the S. pombe genome was published in 2002, by a consortium led by the Sanger Institute, becoming the sixth model eukaryotic organism whose genome has been fully sequenced. S. pombe researchers are supported by the PomBase MOD (model organism database). This has fully unlocked the power of this organism, with many genes orthologous to human genes identified — 70% to date, including many genes involved in human disease. In 2006, sub-cellular localization of almost all the proteins in S. pombe was published using green fluorescent protein as a molecular tag. Schizosaccharomyces pombe has also become an important organism in studying the cellular responses to DNA damage and the process of DNA replication. Approximately 160 natural strains of S. pombe have been isolated. These have been collected from a variety of locations including Europe, North and South America, and Asia. The majority of these strains have been collected from cultivated fruits such as apples and grapes, or from the various alcoholic beverages, such as Brazilian Cachaça. S. pombe is also known to be present in fermented tea, kombucha. It is not clear at present whether S. pombe is the major fermenter or a contaminant in such brews. The natural ecology of Schizosaccharomyces yeasts is not well-studied.
History Schizosaccharomyces pombe was first discovered in 1893 when a group working in a Brewery Association Laboratory in Germany was looking at sediment found in millet beer imported from East Africa that gave it an acidic taste. The term schizo, meaning "split" or "fission", had previously been used to describe other Schizosaccharomycetes. The addition of the word pombe was due to its isolation from East African beer, as pombe means "beer" in Swahili. The standard S. pombe strains were isolated by Urs Leupold in 1946 and 1947 from a culture that he obtained from the yeast collection in Delft, The Netherlands. It was deposited there by A. Osterwalder under the name S. pombe var. liquefaciens, after he isolated it in 1924 from French wine (most probably rancid) at the Federal Experimental Station of Vini- and Horticulture in Wädenswil, Switzerland. The culture used by Urs Leupold contained (besides others) cells with the mating types h90 (strain 968), h- (strain 972), and h+ (strain 975). Subsequent to this, there have been two large efforts to isolate S. pombe from fruit, nectar, or fermentations: one by Florenzano et al. in the vineyards of western Sicily, and the other by Gomes et al. (2002) in four regions of southeast Brazil.
Ecology The fission yeast S. pombe belongs to the division Ascomycota, which represents the largest and most diverse group of fungi. Free-living ascomycetes are commonly found in tree exudates, on plant roots and in surrounding soil, on ripe and rotting fruits, and in association with insect vectors that transport them between substrates. Many of these associations are symbiotic or saprophytic, although numerous ascomycetes (and their basidiomycete cousins) represent important plant pathogens that target myriad plant species, including commercial crops. Among the ascomycetous yeast genera, the fission yeast Schizosaccharomyces is unique because of the deposition of α-(1,3)-glucan or pseudonigeran in the cell wall in addition to the better known β-glucans and the virtual lack of chitin. Species of this genus also differ in mannan composition, which shows terminal d-galactose sugars in the side-chains of their mannans. S. pombe undergo aerobic fermentation in the presence of excess sugar. S. pombe can degrade L-malic acid, one of the dominant organic acids in wine, which makes them diverse among other Saccharomyces strains.
Comparison with budding yeast (Saccharomyces cerevisiae) The yeast species Schizosaccharomyces pombe and Saccharomyces cerevisiae are both extensively studied; these two species diverged approximately 300 to 600 million years before present, and are significant tools in molecular and cellular biology. Some of the technical discriminants between these two species are:
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