Biology subjects

Tiefenbrunner, W.

Publications and source records attributed to Tiefenbrunner, W..

6 recordsLinked to original sources

bioRxiv2024

Pure yeasts selected from fermenting pear juice from the Lower Austrian Mostviertel region and their suitability for pear wine production

If spontaneous fermentation is not carried out, commercially available pure yeasts, which are actually intended for the production of wines from grapes, are often used for the production of pear wines. Pear juice is clearly different from grape juice, e.g. due to the significantly greater difference in the ratio of fructose to glucose or the absence of tartaric acid. For this reason, the commercially available pure yeasts may be suboptimal for pear wine production. They were therefore compared with yeasts isolated from pear juice that had been purely cultivated with regard to their suitability for pear wine production. Overall, the yeasts isolated from fermenting pear juice proved to be more suitable for pear wine production. This is not only the result of the tasting of the wines fermented in 25-litre glass flasks, but also follows very clearly from the multivariate comparison both for the basic chemistry and for the spectrum of aroma components. Density and malic acid concentration were higher in wines produced with yeasts selected from fermenting pear juice. More substances from the "fruity" and especially "fruity-sweet" flavour groups were found in these wines in comparatively higher concentrations. For pear wine production, it is therefore advisable to isolate suitable yeasts from pear juice for pure cultivation.

microbiology↗

bioRxiv2022

Entropy change due to selection in replicator and recombinator systems with randomly chosen interaction matrix values

Selection can be described as a process of information accumulation21. The present work extends this for frequency-dependent selection. For recombination, it is shown that the total entropy change can be calculated by summing the contributions of the individual gene loci in this case as well. For more complex replicator systems with and without recombination with randomly selected interaction matrix values (defining the fitness landscape), a detailed investigation is made of how the number of replicators ("genotypes") surviving, the mean fitness, and the entropy change depend on the number of replicators initially present, on their initial frequencies, and on certain properties (symmetry: aij=aji versus aij=aji) of the interaction matrix. Survival of several to many replicators is the norm rather than the exception. The more survive, the smaller the entropy change due to selection, although this is no longer generally true for asymmetric interaction matrices. Cases deviating from the rule were studied, but their systematic classification is still lacking. Finally, how evolution alters replicator systems of greater complexity was analyzed. It is shown that different evolutionary algorithms can lead to an increase in mean fitness and/or an increase in the number of surviving replicators. In contrast to simple replicator systems, coexistence in more complex ones apparently results naturally as a consequence of selection and evolution. It results that the view that: "Evolution is based on a fierce competition between individuals and should therefore reward only selfish behavior"16 is merely an artifact that follows from the study of unrealistically simple systems.

evolutionary biology↗

bioRxiv2021

Change of information by positive frequency-dependent selection in two very different models (laser-like and chirality of shell-coiling in the snail Partula suturalis)

Although according to the second law of thermodynamics the world tends toward maximum disorder, over millions of years evolution has given rise to an enormous variety of complex organisms. To explain this, one must assume that natural selection is a process of information acquisition. Since some years an information theory of selection exists that can quantify this change and thus helps to understand the apparent contradiction between the existence of biological complexity and the tendency toward disorder that generally prevails in nature. Here I apply this theory to examples of frequency-dependent selection (this means: in which phenotype frequency determines its fitness). The snail Partula suturalis gave an evolutionary and ecologically unique and hence very valuable example of this type of selection before it became extinct about thirty years ago on its native island. Spatially separated populations with left- and right-coiled shells occurred on Moorea, but also hybridization zones. Since both types of shells were the same except for chirality, the question is whether selection happened at all. The inheritance of this character is monogenic and in this respect simple, but is complicated by the fact that it is the maternal genotype, not the own, that determines the phenotype. This causes that for the calculation of the information change by selection not the genotype or phenotype frequencies are sufficient, but one must consider their combination. The simulation shows that frequency-dependent selection in P. suturalis indeed increased information. It has already been shown that selection can also be important outside animate nature, for example in the generation of laser light, which has extraordinary properties: it is monochromatic, monoaxial and monophasic. Phase selection is frequency(=density)-dependent and therefore of interest here. In selection theory the mean fitness {omega} is of special significance. In a laser-like model, in modeling phase selection, we find that {omega}=1+A2, where A2 is the the light intensity or the square of the amplitude, respectively. During selection, {omega} increases and, in parallel, since selection is a process of information acquisition, so does the information. Because of the connection between {omega} and A2 this also means for the laser-like model that - assuming a constant number of photons - a larger amplitude always means more information (less entropy).

evolutionary biology↗

bioRxiv2020

Information change due to natural selection in populations with and without recombination

Though evolution undoubtedly operates in accordance with the second law of thermodynamics, the law of disorder, during billions of years organisms of incredible complexity came into being. Natural selection was described by Darwin2 as a process of optimization of the adaptation to environment, but optimization doesnt necessarily lead to higher intricacy. Methods of thermodynamics and thus of information theory could be suited for the examination of the increase of order and information due to evolution. Here I explain how to quantify the increase of information due to natural selection on the genotype and gene level using the observable change of allele frequencies. In populations with recombination (no linkage), the change of information content can be computed by summing up the contributions of all gene loci and thus gene loci can be treated as independent no matter what the fitness-landscape looks like. Pressure of deleterious mutations decreases information in a linear way, proportional to fitness loss and mutation rate. The information theoretical view on evolution might open new fields of research.

evolutionary biology↗

bioRxiv2018

Fermentation characteristics of mead and wine generated by yeasts isolated from beehives of two Austrian regions

Mead is a traditional alcoholic beverage that is produced by fermentation of diluted honey. The mead quality is primarily influenced by the honey variety, although the yeast microflora as the main catalyst of alcoholic fermentation also plays a significant role in the organoleptic and chemical quality of the final product. The impact of the indigenous honey associated-yeasts on the mead properties has scarcely been investigated. To fill this gap the main objective of this work was to assess the metabolic properties of the yeasts isolated from honey and pollen from beehives of northeast Austria.\n\nThe biodiversity was low and only two yeast species were identified, Zygosaccharomyces rouxii and Candida apicola. The fermentation potentials of these yeasts were estimated in two media, grape juice (since yeasts isolated from honey may be useful for sweet wine production) and diluted honey of similar sugar concentration, and compared with those of the reference strains Saccharomyces cerevisiae; S. uvarum and S. eubayanus. Depending on the fermentation substrate, yeasts differed with respect to their metabolic power, fermentation rate, sugar utilization and production of glycerol and organic acids. During mead fermentation Saccharomyces species showed the highest metabolic turnover, while the fermentation rate did not differ significantly. Addition of assimilable nitrogen to the diluted honey enhanced fermentation rate of S. cerevisiae, but not of the other species. Fermentation of grape juice occurred much faster than that of diluted honey and differences between yeasts were more pronounced. The S. cerevisiae commercial wine strain, adapted to high alcohol concentrations, and S. eubayanus outperformed the others, S. uvarum was comparable with Z. rouxii, while C. apicola had the lowest fermentation rate. Fructophily of Z. rouxii and to a lesser degree of C. apicola was observed in both media. An increased production of glycerol was achieved by S. eubayanus in both media and by C. apicola during the fermentation of honey must. A commercial S. cerevisiae strain, S. eubayanus and Z. rouxii were able to metabolize malic acid in wine. In mead, the S. eubayanus and S. uvarum yeasts showed the tendency of increasing the level of malic acid. Aroma profile depended profoundly on yeast species. This study demonstrates that the composition and complexity of the fermentation substrate determines the activity and the final metabolic outcomes of the studied yeasts.

microbiology↗

bioRxiv2018

Seasonal variation of fermentation rate in Saccharomyces spp. (Ascomycota)?

Yeast species of the genus Saccharomyces show some reaction to visible light - although they lack photo pigments and the typical clock genes of fungi - that can be explained by damage of the cytochrome electron transport chain of the mitochondria. Evidence for a circadian clock, entrainable by cyclic environmental stimuli, exists for periodic changing temperature and light as zeitgeber. Whether seasonality follows from the existence of a circadian clock - which is a necessary requirement for annual rhythms - remains unknown.\n\nDue to an accidental observation, we were able to show that fermentation taking place in complete darkness and at constant temperature is influenced in some yeast strains by the history of the inoculum culture. Using yeast cultures growing on agar plates and exposed to diffuse daylight for three weeks either in March or in May as inoculum, leads to significantly different fermentation rates in the inoculated grape juice in both months: rates are higher in March when day length is shorter than in May. In must inoculated with cultures that grew in darkness or daylight, respectively, higher fermentation rates occur by the former. Other yeast strains react to artificial white light in the same way.\n\nWe used strains of S. cerevisiae, S. eubayanus, S. kudriavzevii, S. uvarum and furthermore hybrid strains of two or even three of these species. The most pronounced reaction to daylight was shown by the S. eubayanus x S. uvarum x S. cerevisiae hybrid, followed by S. cerevisiae x S. kudriavzevii hybrids, S. eubayanus and S. cerevisiae. S. uvarum was sensitive to artificial white light.\n\nThese observations can hardly be explained by some kind of photo damage because they base on an effect that persists through many cell division cycles after yeasts were exposed to light. If it really represents seasonality epigenetic memory is likely involved, since fermentation lasts for many days and yeast generations. If the existence of a circadian clock and seasonal behaviour in Saccharomyces is confirmed these yeasts could become an important tool in basic research concerning epigenetic memory.

microbiology↗