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Yeast Biotechnology in JapanA series of minireviews on the potential industrial applications of yeasts
 In Japan, many species of micro-organisms have been used safely in more than 1000 years in the manufacture of various products, including sake (Japanese rice wine), soy sauce and miso (fermented soybean paste). Fermentation and bioprocessing technology has been a major strength of the Japanese Industry for a long time. Japanese industry has also been involved in the breeding of micro-organisms for many years to improve flavour, fragrance and productivity by the use of traditional technology. For example, there are many strains of yeasts available for the production of sake, mainly Saccharomyces cerevisiae strains called 'Yeast Kyokai No. x'. DNA sequencing technology will bring the development of new manufacturing technologies for various fermented and brewed foodstuffs. S. cerevisiae was, in 1996, the first eukaryote to have its genome completely sequenced. At present, the genome sequence data for the fission yeast Schizosaccharomyces pombe and other yeasts are available. Furthermore, the genome sequence project for sake yeast (S. cerevisiae) has been conducted by a Japanese institute. Yeasts have become important players in industrial application and also systems biology. Recent progress in gene expression technology, metabolic engineering technology and the like has contributed the improvement in micro-organisms. Yeasts, especially, combine the advantages of a unicellular eukaryotic micro-organism with the ability to carry out post-translational modifications such as protein folding. Yeasts have been used for the production of various proteins. S. cerevisiae, however, has some disadvantageous properties, including the retention of products within the periplasmic space, hyperglycosylation of the products and pH-sensitivity. The methylotrophic yeasts Hansenula polymorpha and Pichia pastoris, the asporogenous methylotrophic yeast Candida boidinii and the fission yeast S. pombe have been used for protein production as non-conventional yeasts. Such yeasts have been used for the production of chemicals, pharmaceuticals and industrial enzymes. Recombinant human serum albumin has been produced in Pichia pastoris (and was approved in Japan as a pharmaceutical in 2007). The S. pombe expression system has been used for the production of clinical materials and commercial production of animal-feed enzymes. Evolution has resulted in the appearance of huge variety of micro-organisms living in different environments. Some of these micro-organisms have evolved their metabolic pathways to produce some metabolites very efficiently. Recent progress in genome engineering technology has provided a powerful tool with which to encourage the evolution of micro-organisms, leading to the manufacture of various products in large quantities. One example of metabolic engineering is the production of lactic acid in S. cerevisiae. Recombinant yeasts that have been engineered for the industrial production of lactic acid have been described by Japanese researchers. Recent research – the so-called MGF (Minimum Genome Factory) project – in Japan has led to a reduction in the time needed for the deletion of unnecessary genes. The goal of the MGF project is to construct a minimum-genome micro-organism as a cell factory to produce various proteins and chemicals efficiently. MGF technology could improve microbial strains at the chromosomal level. Such innovative technology has a huge potential for the production of not only various pharmaceuticals and fine chemicals, but also biofuels. Metabolic engineering technology, including MGF, will offer an innovative approach to solving energy problems. The collected minireviews in this series represent an update of knowledge, by experts in Japan, that has accumulated on yeasts, which are eukaryotic unicellular microfungi widely distributed in natural environments. During the fermentation of the production of baker's yeast (S. cerevisiae), cells are exposed to numerous environmental stresses, such as freeze-thaw, air-drying and oxidative stresses. Shima and Takagi have reviewed stress-tolerance mechanisms based on stress protectants as well as the genes required for stress tolerance examined by post-genomic analyses. The functional characterization of brewing yeasts during fermentation remains an important goal for the brewing industry. However, changes in yeast cells under ethanol stress or in alcohol brewing have not been fully elucidated. Post-transcriptional events (Izawa and Inoue) and mitochondrial morphology (Kitagaki) under ethanol-stress conditions are also described. CoQ (coenzyme Q) is now commercially popular as a food supplement. Yeasts possess different species of CoQ depending on the length of the isoprenoid side chains (S. pombe, CoQ10, ten side chains; C. albicans, CoQ9; C. utilis, CoQ7; and S. cerevisiae, CoQ10). In his minireview, Kawamukai focuses on the biosynthesis of CoQ in yeasts. The popularity of the heterologous gene expression system by yeasts has increased in both the academic and industrial fields. Recent developments in efficient heterologous protein production systems using methylotrophic (Yurimoto and Sakai) and fission (Takegawa et al.) yeasts are described. While the conventional yeasts have been used in biotechnological processes, non-conventional yeasts have recently become increasingly important. Biosurfactants produced by various micro-organisms show unique properties and have attracted interest because of the variety of their functions. Morita et al. describe the production and application of mannosylerythritol lipids produced by basidiomycetous yeasts. We extend our special thanks all of the authors who have written minireviews on these various topics. These minireviews are aimed at bringing together material on the diversity of yeasts in both normal and extreme environments, yeast physiology and biochemistry, molecular aspects and biotechnological applications.
The Reviews Editor and the Executive Editor of Biotechnology and Applied Biochemistry extend their warmest thanks to Professor Diethard Mattinovich (Department of Biotechnology, Institute of Applied Microbiology, University of Natural Resources and Applied Life Sciences, Vienna, Austria), who kindly acted as Guest Editor for this series of Minireviews. |
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