Abstract
In this thesis, the viability of the yeast species Saccharomyces paradoxus was investigated
by examining the metabolic profile of energy metabolism in their natural habitat using FTICR-
MS. For this purpose, different yeast strains of the species Saccharomyces paradoxus
were cultivated in the yeast medium, which was collected from their natural habitat at five
different seasons and two different substrates (soil and leaf litter) and compared at three
timepoints after yeast cell addition (T0, T05, T24).
The results of the work may partially confirm the findings that glycolysis and the citrate cycle
are the main energy metabolism of yeasts. In addition, new insights are given that allow the
use of alternative energy sources by Saccharomyces paradoxus and the course of
metabolic pathways, enabling them to survive in nature in the absence of sugars. In the
PCA models, differentiations were observed at time T05 on the one hand and in the seasons
on the other, with cluster formation at November 2017.
Through the extracellular examination of the metabolite spectrum of Saccharomyces
paradoxus, the use of alternative substances as energy sources, the connections and
functions to each other and to the energy metabolism could be partially elucidated.
The energy metabolism of yeasts is very diverse, especially when using compounds that
can serve as energy sources. Nevertheless, within the scope of this work, slight insights
into these have been made possible. Since glycolysis is described as one of the main
energy metabolisms of yeasts, it is surprising that only two metabolites, acetaldehyde and
lactate, could be identified. However, this can be attributed to the presence of furfural, which
has an inhibitory effect on glycolysis. The detection of lactate can be traced back to a
possible self-synthesis by yeasts, which occurs independently of the substrate. Also, a
conversion of lactaldehyde or the reaction of acetaldehyde can lead to lactate production.
Lactate can then serve as a precursor of glycerol, which is then used as an energy source.
The identification of cis-aconitate, succinate and isocitrate or citrate suggests that
Saccharomyces paradoxus operates the citrate cycle as an energy metabolism. However,
these compounds also occur in the glyoxylate bypass, which enables the growth of
microorganisms in the absence of sugars.
Yeasts mainly produce glycerol as a by-product of sugar metabolism and can be regulated
by various nutritional and environmental factors such as temperature, osmosis and nitrogen
source. Through de novo synthesis, yeasts can synthesize glycerol themselves, which they
use and degrade under aerobic conditions as a source of energy and carbon. The presence
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of DMSO can also lead to glycerol production, since yeasts form balancing substances such
as glycerol to protect cells against oxidative stress.
Nitrogen sources are required for yeast growth and TCA, influence glycerol production in
yeast cells and can promote lipid production, which yeast can then use as an energy source.
Urea could serve as a nitrogen source, release toxic compounds from yeast cells or
increase fatty acid production. The degradation of creatinine may suggest that this
compound is used as an energy source by Saccharomyces paradoxus.
The function of fatty acids such as lauric acid, palmitic acid and stearic acid is that they can
be used for membrane synthesis, prostaglandin formation and as a source of energy
through Saccharomyces paradoxus. Likewise, the influence of growth temperature can
have an effect on the presence of fatty acids in the culture medium, so that the behaviour
and presence of fatty acids cannot be generalized.
