Biomedical subjects

G P Casey

Publications and source records attributed to G P Casey.

4 recordsLinked to original sources

PubMed1991

Polymorphism within the nuclear and 2 micron genomes of Saccharomyces cerevisiae.

Seven strains of bakers' yeast were obtained as a representative sample of the Spanish baking industry. The nuclear genome was monitored for polymorphism by transverse alternating field electrophoresis (TAFE) and restriction maps of 2 micron DNA were produced. All seven strains were uniquely different when evaluated by their total chromosomal lengths whereas only two 2 micron variants were defined. There was no apparent correlation between chromosomal and plasmid polymorphism. The extensive chromosomal polymorphism within one 2 micron DNA type indicates the rapid and relatively recent evolution of the nuclear genome. The hybrid origin (S. cerevisiae-S. monacensis) of lager yeast was critically evaluated by TAFE analysis of S. cerevisiae and S. carlsbergensis chromosomes. The absence of corresponding S. cerevisiae chromosomes III and XIII in S. carlsbergensis argued against the hybrid origin of lager strains. We discuss limitations of the hybrid origin hypothesis of industrial yeasts and propose that the molecular coevolution observed in 2 micron DNA serves as a useful additional mechanism for rationalization of some of the structural polymorphism of the nuclear genome.

Chromosomes, Fungal↗

PubMed1988

DNA sequence polymorphisms in the genus Saccharomyces. V. Cloning and characterization of a LEU2 gene from S. carlsbergensis.

Saccharomyces carlsbergensis strains used in the production of lager beer are structurally heterozygous in most genetic loci studied to date. Previous studies have shown that the genotype of lager yeast contains two types of genomes, one of which is derived from S. cerevisiae and the other reveals similarities to the genomes of S. bayanus and S. monacensis. Genes of homeologous chromosomes can be distinguished by characteristic restriction fragment patterns. This is true also for the LEU2 genes which encode the beta-isopropylmalate dehydrogenase and are located on chromosomes III. In the present work a LEU2 gene from S. carlsbergensis has been cloned and characterized. The cloned 2.6 kb LEU2 region complements the S. cerevisiae leu2-3 leu2-112 double mutation. The restriction endonuclease site map of the isolated S. carlsbergensis LEU2 gene is different from that of the S. cerevisiae LEU2 gene. Electrophoretic chromosome separation, as well as karl mediated transfer of single chromosomes into S. cerevisiae strains, has shown that the S. carlsbergensis specific LEU2 gene is located on a chromosome III which carries the carlsbergensis specific HIS4 gene. The cloned LEU2 gene shows preferential molecular hybridization to one of the two LEU2 structural alleles present in lager strains, an allele which is also present in type strains of S. bayanus, S. carlsbergensis, S. monacensis and S. uvarum.

Alleles↗

PubMed1986

Ethanol tolerance in yeasts.

It is now certain that the inherent ethanol tolerance of the Saccharomyces strain used is not the prime factor regulating the level of ethanol that can be produced in a high sugar brewing, wine, sake, or distillery fermentation. In fact, in terms of the maximum concentration that these yeasts can produce under batch (16 to 17% [v/v]) or fed-batch conditions, there is clearly no difference in ethanol tolerance. This is not to say, however, that under defined conditions there is no difference in ethanol tolerance among different Saccharomyces yeasts. This property, although a genetic determinant, is clearly influenced by many factors (carbohydrate level, wort nutrition, temperature, osmotic pressure/water activity, and substrate concentration), and each yeast strain reacts to each factor differently. This will indeed lead to differences in measured tolerance. Thus, it is extremely important that each of these be taken into consideration when determining "tolerance" for a particular set of fermentation conditions. The manner in which each alcohol-related industry has evolved is now known to have played a major role in determining traditional thinking on ethanol tolerance in Saccharomyces yeasts. It is interesting to speculate on how different our thinking on ethanol tolerance would be today if sake fermentations had not evolved with successive mashing and simultaneous saccharification and fermentation of rice carbohydrate, if distillers' worts were clarified prior to fermentation but brewers' wort were not, and if grape skins with their associated unsaturated lipids had not been an integral part of red wine musts. The time is now ripe for ethanol-related industries to take advantage of these findings to improve the economies of production. In the authors' opinion, breweries could produce higher alcohol beers if oxygenation (leading to unsaturated lipids) and "usable" nitrogen source levels were increased in high gravity worts. White wine fermentations could also, if desired, match the higher ethanol levels in red wines if oxygenation (to provide the unsaturated lipids deleted in part by the removal of the grape skins) were practiced and if care were given to assimilable nitrogen concentrations. This would hold true even at 10 to 14 degrees C, and the more rapid fermentations would maximize utilization of winery tankage.(ABSTRACT TRUNCATED AT 400 WORDS)

Ethanol↗

PubMed1984

High-gravity brewing: effects of nutrition on yeast composition, fermentative ability, and alcohol production.

A number of economic and product quality advantages exist in brewing when high-gravity worts of 16 to 18% dissolved solids are fermented. Above this level, production problems such as slow or stuck fermentations and poor yeast viability occur. Ethanol toxicity has been cited as the main cause, as brewers' yeasts are reported to tolerate only 7 to 9% (vol/vol) ethanol. The inhibitory effect of high osmotic pressure has also been implicated. In this report, it is demonstrated that the factor limiting the production of high levels of ethanol by brewing yeasts is actually a nutritional deficiency. When a nitrogen source, ergosterol, and oleic acid are added to worts up to 31% dissolved solids, it is possible to produce beers up to 16.2% (vol/vol) ethanol. Yeast viability remains high, and the yeasts can be repitched at least five times. Supplementation does not increase the fermentative tolerance of the yeasts to ethanol but increases the length and level of new yeast cell mass synthesis over that seen in unsupplemented wort (and therefore the period of more rapid wort attenuation). Glycogen, protein, and sterol levels in yeasts were examined, as was the importance of pitching rate, temperature, and degree of anaerobiosis. The ethanol tolerance of brewers' yeast is suggested to be no different than that of sake or distillers' yeast.

Journal Article↗