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 Tolerance in Yeasts

The inhibitory effect of butanol on yeast growth has been studied for the strain Candida utilis ATCC 8205 growing aerobically on butanol under batch conditions. A mathematical expression was then proposed to fit the kinetic pattern of butanol inhibition on the specific growth rate: micro = micro mS/Ks + S [1 - S/Sm]n. The maximum allowable butanol concentration above which cells do not grow was predicted to be 9.16g/L. The proposed model appears to accurately represent the experimental data obtained in this study and the literature data developed for a variety of batch culture systems at widely ranging substrate concentrations.

Generalization of monod kinetics for analysis of growth data with substrate inhibition.

This study examined the hypothesis that solid surfaces may stimulate attached bacteria to produce exopolymers. Addition of sand to shake-flask cultures seemed to induce exopolymer synthesis by a number of subsurface isolates, as revealed by optical microscopy. Several additional lines of evidence indicated that exopolymer production by attached cells (in continuous-flow sand-packed columns) was greater than by their free-living counterparts. Total carbohydrates and extracellular polysaccharides, both normalized to cell protein, were greater (2.5- and 5-fold, respectively) for attached cells than for free-living cells. Also, adsorption of a polyanion-binding dye to the exopolymer fraction was sixfold greater for attached cells than for unattached cells. When surface-grown cells were resuspended in fresh medium, exopolymer production decreased to the level characteristic of unattached cells, which ruled out the possibility that attached cells comprised a subpopulation of sticky mucoid variants. The mechanism by which attachment stimulated exopolymer synthesis did not involve changes of the specific growth rate, growth stage, or limiting nutrient.

Attachment Stimulates Exopolysaccharide Synthesis by a Bacterium

Biological principles for the effects of ethanol

Columns were packed with clean quartz sand, sterilized, and inoculated with different strains of bacteria, which multiplied within the sand at the expense of a continuous supply of fresh nutrient medium. The saturated hydraulic conductivity (HCsat) of the sand was monitored over time. Among the four bacterial strains tested, one formed a capsule, one produced slime layers, and two did not produce any detectable exopolymers. The last two strains were nonmucoid variants of the first two. Only one strain, the slime producer, had a large impact on the HCsat. The production of exopolymers had no effect on either cell multiplication within or movement through the sand columns. Therefore, the HCsat reduction observed with the slime producer was tentatively attributed to the obstruction of flow channels with slime. Compared with the results with Arthrobacter sp. strain AK19 used in a previous study, there was a 100-fold increase in detachment from the solid substratum and movement through the sand of the strains used in this study. All strains induced severe clogging when they colonized the inlet chamber of the columns. Under these conditions, the inlet end was covered by a confluent mat with an extremely low HCsat.

Effect of bacterial extracellular polymers on the saturated hydraulic conductivity of sand columns

Fifteen bacterial strains and four molds capable of growth on n-butane were isolated and partially classified The bacteria were mostly Arthrobacter sp and Brevibacterium sp; among the molds, Pen

Isolation and characterization of n-butane-utilizing microorganisms.

Two Candida species and a Saccharomyces were grown on ethyl alcohol, acetic acid, ethyl acetate, and 1-butanol, and their growth rates at a series of concentrations of each substrate are reported. ...

Kinetics of yeast growth:inhibition-threshold substrate concentrations.

Intracellular structures were observed in two Arthrobacter spp. and in Candida utilis in media containing n-butane or 1-butanol as the sole source of carbon; these structures were absent in the sam...

Characteristic cytoplasmic structures in microorganisms utilizing n-butane and l-butanol.

Soluble proteins were extracted from the vegetative cells of four pentose-fermenting yeasts, Candida shehatae, Pichia stipitis, R-1, and R-2, the R strains being of uncertain taxonomy, while the other two are culture collection yeasts. Isoenzyme patterns, protein patterns, and two-dimensional polypeptide mapping of these four strains were compared by polyacrylamide gel electrophoresis. The two R strains showed great similarity in two-dimensional polypeptide mapping, the pattern of sodium dodecyl sulfate – polyacrylamide gel electrophoresis, isoelectrofocusing, and isoenzymes, and may be one species. Each of the other two yeasts had its own characteristic electrophoretic pattern. The R strains showed the presence of three alcohol dehydrogenase isoenzymes compared with one for the culture collection yeasts, as well as much higher activity of malate dehydrogenase, isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase, which further the formation of pyruvate and eth...

Isoenzyme and protein patterns of pentose-fermenting yeasts

Samples of two streams, a primary oxidation product and a main recycle stream, were obtained from a large industrial plant oxidizing butane. These are not wastes, but streams within the production ...

Morris Wayman

Papers

Isolation and characterization of n-butane-utilizing microorganisms.

Kinetics of yeast growth:inhibition-threshold substrate concentrations.

Characteristic cytoplasmic structures in microorganisms utilizing n-butane and l-butanol.

Isoenzyme and protein patterns of pentose-fermenting yeasts

Butane-oxidation products as substrates for yeast growth