Introduction
There has been a growing interest towards creating defined mixed starter cultures for alcoholic fermentations. Previously, metabolite differences between single and mixed cultures have ...been explored at the endpoint of fermentations rather than during fermentations.
Objectives
To create metabolic footprints of metabolites that discriminate single and mixed yeast cultures at two key time-points during mixed culture alcoholic fermentations.
Methods
1
H NMR- and GC–MS-based metabolomics was used to identify metabolites that discriminate single and mixed cultures of
Lachancea thermotolerans
(LT) and
Saccharomyces cerevisiae
(SC) during alcoholic fermentations.
Results
Twenty-two metabolites were found when comparing single LT and mixed cultures, including both non-volatiles (carbohydrate, amino acid and acids) and volatiles (higher alcohols, esters, ketones and aldehydes). Fifteen of these compounds were discriminatory only at the death phase initiation (T1) and fifteen were discriminatory only at the death phase termination (T2) of LT in mixed cultures. Eight metabolites were discriminatory at both T1 and T2. These results indicate that specific metabolic changes may be descriptive of different LT growth behaviors. Fifteen discriminatory metabolites were found when comparing single SC and mixed cultures. These metabolites were all volatiles, and twelve metabolites were discriminatory only at T2, indicating that LT-induced changes in volatiles occur during the death phase of LT in mixed cultures and not during their initial growth stage.
Conclusions
This work provides a detailed insight into yeast metabolites that differ between single and mixed cultures, and these data may be used for understanding and eventually predicting yeast metabolic changes in wine fermentations.
The corn smut fungus
serves as a model species for studying fungal dimorphism and its role in phytopathogenic development. The pathogen has two growth phases: a saprobic yeast phase and a pathogenic ...filamentous phase. Dimorphic transition of
involves complex processes of signal perception, mating, and cellular reprogramming. Recent advances in improvement of reference genomes, high-throughput sequencing and molecular genetics studies have been expanding research in this field. However, the biology of other non-model species is frequently overlooked. This leads to uncertainty regarding how much of what is known in
is applicable to other dimorphic fungi. In this review, we will discuss dimorphic fungi in the aspects of physiology, reproductive biology, genomics, and molecular genetics. We also perform comparative analyses between
and other fungi in Ustilaginomycotina, the subphylum to which
belongs. We find that lipid/hydrophobicity is a potential common cue for dimorphic transition in plant-associated dimorphic fungi. However, genomic profiles alone are not adequate to explain dimorphism across different fungi.
We demonstrate a new strategy for the label-free monitoring of yeast cell growth and its interaction with drugs using simple bending-mode of polymer microcantilever biosensors. Saccharomyces ...cerevisiae strains YN94-1 and YN94-19 were deposited onto microcantilever sensor surfaces and the growth curves corresponding to the bending were investigated under different culture conditions. The real-time polymer microcantilever bending signal revealed distinct growth characteristics of cells cultured in Synthetic Complete (SC) medium with and without the addition of uracil and 5′-fluororotic acid, which are indiscernible using conventional screening methods. In addition, cantilever deflection signals of up to ∼7μm were observed, which can only be explained through surface stress interactions between yeast cells and the polymer cantilevers due to the enhanced sensitivity of the viscoelastic polymer cantilevers. This new method of enhanced sensitivity in static mode microcantilever monitoring of cell growth opens opportunities for highly sensitive applications in the fields of disease diagnosis and drug discovery and testing.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Yeast cell death is triggered when essential nutrients such as potassium and lipid are limited but ammonium is in excess. When ammonium and glucose were maintained at 100% of the normal concentration ...while all the other essential nutrients in yeast nitrogen base (YNB) were reduced to 2%, yeast growth was halted by ammonium toxicity. Yeast started to grow again when either ammonium was also reduced to 2% or gluconate was added, but simultaneously adding gluconate as well as reducing all the nutrients except glucose 50-fold revived yeast growth to a greater extent, i.e. a quarter of the normal growth. Gluconate, as well as formate and alginate, stimulated yeast growth by buffering the drop in pH. Yeast cells were seemingly more susceptible to low pH under the nutrient-limited conditions, entering the stationary phase at pH higher than that of the normal condition. Carboxylate salts may prove a cost-efficient replacement for large proportions of the essential nutrients as yeast cells, in the presence of 2 mg ml
−1
gluconate, could still achieve nearly 90% of the normal growth when cultured in only 10% of the normal YNB concentration.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This study characterizes the effects of oxygen transfer on the growth and carotenoid (astaxanthin) production of the red yeast
Phaffia rhodozyma in liquid cultures. The yeast culture on a liquid ...medium at 20
°C had a critical dissolved oxygen (DO) concentration of 10% air-saturation (0.8
mg/L) and a maximum specific oxygen uptake rate of 60
mg O
2/g
cell
h. In 250-mL shake-flasks with 50
ml liquid medium, poor oxygen transfer resulted in constantly lower DO level than the critical DO in the culture. Both the biomass and carotenoid yields increased with the decrease in liquid volume in flasks and the increase in shaker speed, e.g., 8.0
g dw/L biomass and 7.4
mg/L carotenoid with 50
mL liquid at 200
rpm versus 10.7
g dw/L biomass and 15.5
mg/L carotenoid with 20
mL liquid at 250
rpm. The oxygen transfer coefficient (
K
L
a) was correlated to shaker speed (
N) and liquid volume (
V
L) by
K
L
a
=
0.141
N
0.88
(
V
L
/V
o)
−0.80 based on linear regression of experimental data (
R
2
=
0.997,
V
o
=
flask volume). The carotenoid yield showed a strong linear correlation with the oxygen transfer rate (
R
2
=
0.989). These results show that oxygen supply is crucial for carotenoid production in
P. rhodozyma liquid cultures.
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Winemaking is a stressful procedure for yeast cells. The presence of high levels of carbohydrates at the beginning of the fermentation and the subsequent increase of ethanol levels alongside with ...other environmental factors force the cell to undergo a continuous adaptation process. Ideally, yeast strains should be able to adapt to this changing environment fast and they must be able to ferment at low temperatures with the highest possible fermentation rates. Additionally, the balanced utilization of glucose and fructose-the two major hexoses in grapes-is also important as any residual fructose may confers unwanted sweetness. As proteins, Msn2/4 are known to play pivotal roles in cell stress response, the question that arise regards the differentially cell response driven by specific point mutations in these two proteins, and the subsequent effects on alcoholic fermentation. Four different mutants in which serine residues have been replaced by alanine are studied in this paper. Our results indicate that substitution at position 533 of Msn4 protein (W_M4_533) significantly increases the fermentation rate even at low temperatures (12 °C), by lowering the fermentation's activation energy. Similar results but to a lesser extent were obtained by the S582A substitution in Msn2 protein. In addition, W_M4_533 seems to have a more balanced utilization of must hexoses. From the present work it is concluded that genetic modification Msn2/4 represents a promising procedure for shortening the fermentation time, even at low temperatures, which in many cases constitutes an important technological requirement.
For the investigation of protein localization and trafficking using live cell imaging, researchers often rely on fusing their protein of interest to a fluorescent reporter. The constantly evolving ...list of genetically encoded fluorescent proteins (FPs) presents users with several alternatives when it comes to fluorescent fusion design. Each FP has specific optical and biophysical properties that can affect the biochemical, cellular, and functional properties of the resulting fluorescent fusions. For instance, several FPs tend to form nonspecific oligomers that are susceptible to impede on the function of the fusion partner. Unfortunately, only a few methods exist to test the impact of FPs on the behavior of the fluorescent reporter. Here, we describe a simple method that enables the rapid assessment of the impact of FPs using polyglutamine (polyQ) toxicity assays in the budding yeast Saccharomyces cerevisiae. PolyQ-expanded huntingtin proteins are associated with the onset of Huntington's disease (HD), where the expanded huntingtin aggregates into toxic oligomers and inclusion bodies. The aggregation and toxicity of polyQ expansions in yeast are highly dependent on the sequences flanking the polyQ region, including the presence of fluorescent tags, thus providing an ideal experimental platform to study the impact of FPs on the behavior of their fusion partner.
Dough fermentation is a process very similar to the expansion of a pseudoplastic foam, in which initial germs (yeast) are quasi-homogeneously distributed. The present model considers the expansion as ...a chemical reaction, which producing gas leads to the growth and the coalescence of bubbles, which form in the pseudoplastic paste, thus conferring to the loaf its final volume. The fermentation kinetic was investigated by monitoring the variation of the dough volume vs time by means of image analysis. The leavening process can be divided into three stages: the lag stage, a positive acceleration stage and a negative acceleration stage. Aim of the model developed in this study was described the variation of dough volume
y as a function of time t, i.e.
y
=
f(
t). A modified Gompertz model was chosen as the best descriptive model of the leavening process. Quite good agreement was observed between experimental data and model parameters.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Inherited 5-oxoprolinase (OPLAH) deficiency is a rare inborn condition characterised by 5-oxoprolinuria. To date, three
OPLAH
mutations have been described: p.H870Pfs in a homozygous state, which ...results in a truncated protein, was reported in two siblings, and two heterozygous missense changes, p.S323R and p.V1089I, were independently identified in two unrelated patients. We describe the clinical context of a young girl who manifested 5-oxoprolinuria together with dusky episodes and who is compound heterozygote for two novel
OPLAH
variations: p.G860R and p.D1241V. To gain insight into the aetiology of the 5-oxoprolinase deficiency, we investigated the pathogenicity of all the reported missense mutations in the
OPLAH
gene. A yeast in vivo growth assay revealed that only p.S323R, p.G860R and p.D1241V affected the activity of the enzyme.
Conclusion
: Taken together, this report further suggests that hereditary 5-oxoprolinase deficiency is a benign biochemical condition caused by mutations in the
OPLAH
gene, which are transmitted in an autosomal recessive manner, but 5-oxoprolinuria may be a chance association in other disorders.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, VSZLJ, ZAGLJ
Growth and thermal inactivation curves were obtained for Zygosaccharomyces bailii in acidified aqueous systems resembling low sugar products. Growth curves were modeled using Gompertz equation while ...thermal inactivation curves were fitted with the Baranyi equation. The parameters of the models were estimated and used to establish the effect of aspartame and other additives (sorbate, xylitol and glucose) on the growth and survival of Z. bailii. Aspartame addition produced different effects on growth rate depending on the solute added and the potassium sorbate concentration. The joint use of xylitol and aspartame showed the lowest growth rates in the absence or in the presence of 0.005% w/w sorbate. Regardless of subinhibitory levels of KS, the addition of aspartame increased the population of the stationary phase of the systems containing glucose or xylitol, suggesting that Z. bailii metabolizes aspartame. The use of aspartame increased the thermal inactivation rates of all systems. Glucose or xylitol addition to the system containing aspartame and sorbate increased the heat sensitivity of Z. bailii. In the absence of sorbate, only glucose decreased the heat resistance of the yeast, whereas xylitol did not affect it. The results obtained highlight the importance of considering the effect of system composition when evaluating microbial stability of food systems.
•Aspartame effect on growth and death of Z. bailii in low sugar systems was studied.•Aspartame generally increased the stationary phase of Z. bailii population.•The joint use of xylitol and aspartame showed the lowest Z. bailii growth rates.•Aspartame increased Z. bailii thermal inactivation rate.
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