Yeasts inducible resistance

Studies have been performed on an isolate of the yeast S. lipolytica with artificially induced resistance as a model system. No evidence has been found that uptake kinetics, enhanced metabolic degradation or target mutation are responsible for resistance, but changes in fatty acid composition have been observed. 

Mutation. For industrial appHcations, mutations are induced by x-rays, uv irradiation or chemicals (iiitrosoguanidine, EMS, MMS, etc). Mutant selections based on amino acid or nucleotide base analogue resistance or treatment with Nystatin or 2-deoxyglucose to select auxotrophs or temperature-sensitive mutations are easily carried out. Examples of useful mutants are strains of Candida membranefaciens, which produce L-threonine Hansenu/a anomala, which produces tryptophan or strains of Candida lipolytica that produce citric acid. An auxotrophic mutant of S. cerevisiae that requires leucine for growth has been produced for use in wine fermentations (see also Wine). This yeast produces only minimal quantities of isoamyl alcohol, a fusel oil fraction derived from leucine by the Ehrlich reaction (10,11). A mutant strain of bakers yeast with cold-sensitive metaboHsm shows increased stabiUty and has been marketed in Japan for use in doughs stored in the refrigerator (12). 

Masison, D. C., and Wickner, R. B. (1995). Prion-inducing domain of yeast Ure2p and protease resistance of Ure2p in prion-containing cells. Science 270, 93-95. 

Eukaryotic Yeast plasmid or integration into host chromosome by homologous recombination Transient or permanent Amino acid requirement in autotrophic strain heavy metal induction of resistance gene Yeast ori sequence constitutive or inducible promoter transcription terminator... 

McDougall, K.J. Lemontt. J.F. (1979) Effects of spermine on the detection of induced forward mutation at the can locus in yeast evidence for selection against canavanine-resistant mutants. Mutat. Res.. 63. 21-34... 

Her research interests originally focused on biological cell membranes, first working on phosphate transport in Escherichia coli and then the plasma membrane proton ATPase in Saccharomyces cerevisiae. While isolating vanadate-resistant mutants in yeast, she became fascinated with work showing that oral administration of vanadium salts alleviated symptoms of diabetes and switched her research focus to that area. She has pursued the insulin-enhancing mechanism of vanadium salts and complexes in cell culture, the STZ-induced diabetic rat, and human type 2 diabetic patients. The National Institutes of Health, the American Heart Association, and the American Diabetes Association have funded the work in her laboratory. Willsky has lectured all around the world and published both research articles and book chapters in this area. 

Photodynamic ACT (PACT), similar to photodynamic therapy (PDT) described in Chapter 17, utilizes photosensitizers and visible or UV light in order to induce a phototoxic response, usually via oxidative damage. For some time the disinfection of blood products, particularly for viral inactivation, has been the major use of PACT, although more and more clinically based protocols are being developed, eg in the treatment of oral infections. The technique has been shown to be effective in vitro against bacteria (including drug resistance strains), yeasts, viruses, and parasites. 

In many countries, alcoholic fermentation is induced by inoculation with a yeast starter culture of Saccharomyces selected for its desirable winemaking qualities (Kunkee, 1984 Kunkee and Bisson, 1993 Rainieri and Pretorius, 2000 Reed and Chen, 1978 Reed and Nagodawithana, 1988). Starter cultures of S. cerevisiae strains are generally used because of to their increased ethanol and sulfur dioxide resistance and production of desirable aromas and flavors (Boulton et al., 1996 Ebeler, 2001 Nykanen, 1986 Reed and Chen, 1978 Reed and Nagodawithana, 1988). 

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