Article

The growth behavior of the model eukaryotic yeast Saccharomyces cerevisiae in microgravity

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Abstract

Saccharomyces cerevisiae is an eukaryotic model organism that has been used for space biology research. Microgravity is a tool to study yeast mechanobiology by removing the gravitational force on the cells. Yeast cells possess mechanosensors that can sense mechanical forces. The cells transduce a mechanical stimulus into a specific cellular response by activating intracellular signaling pathways that can ultimately lead to an altered function. Microgravity is "sensed" by yeast cells as a stress condition and several mitogen-activated protein kinases (MAPK) signaling pathways are activated, including the cell wall integrity (CWI)/protein kinase C (PKC), the high osmolarity glycerol (HOG) and the target of rapamycin (TOR) pathways. One of the indicators of morphological changes is an increase at random bud scar profile. Microgravity influences on the growth rate of yeast cells have been observed. The colony growth rate of the agar invasive S. cerevisiae �1278b strain was reduced as well as its agar invasiveness. Post-flight growth experiments of a brewer's top yeast strain showed an increase in G2/M and a decrease in Sub-G1 cell population; an increased viability, a decreased lipid peroxidation level, increased glycogen content, and changes in carbohydrate metabolic enzyme activities were also observed. Using the S. cerevisiae BY4741 deletion collection, genes that provide a survival advantage in space, were identified in a batch growth experiment; no difference in growth rate was observed. Freeze-dried strains showed significant changes in the cell wall thickness. Spaceflight unique gene expression changes were observed in stress response element (STRE) genes with transcription regulation involving Sfp1 (which is involved in the TOR pathway) and Msn4. Some of the components of the ribosome biogenesis (which is under the control of Sfp1) as well as components of the proteasome were down regulated in microgravity. Recent results indicate that microgravity imposes a "microgravity" stress on the cells, which has the characteristics of an osmotic stress. Cellular energy is directed towards protective measures such as cell wall biosynthesis (CWI pathway activation) and the production of compounds (glycerol, trehalose) that increase the osmotolerancy (HOG pathway).

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... Decreases in the levels of structural ribosomal proteins involved in cytoplasmic translation (i.e., L23a, L37a, and L34) and of the poly(A)polymerase, as well as the increase in RNA degrading ribonuclease T1, were additionally detected in microgravity. Together, the regulation of these proteins may suggest that protein translation via ribosomal translational machinery is reduced upon exposure to LSSMG, a phenomenon that has been indicated as a widespread response to microgravity, space, and Mars-like conditions not only in fungi (Sheehan et al., 2007;Willaert, 2013;Feger et al., 2016;Kamal et al., 2018Kamal et al., , 2019Blachowicz et al., 2019a). Remarkably, in our study, a decrease in translation and ribosome biogenesis was only observed in the wild type whole-cell proteome and, to a minor extent, in the mutant secretome ( Figure 5B). ...
... Also in the mutant, the upregulation of hydrolytic enzymes such as the alpha, alpha-trehalase suggests a recourse to store carbohydrates as a carbon source. By contrast, production of compounds that increase the osmotolerancy (e.g., trehalose) represents a quite common protective measure implemented by microorganisms under microgravity and other types of stress (Willaert, 2013). ...
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... Decreases in the levels of structural ribosomal proteins involved in cytoplasmic translation (i.e., L23a, L37a, and L34) and of the poly(A)polymerase, as well as the increase in RNA degrading ribonuclease T1, were additionally detected in microgravity. Together, the regulation of these proteins may suggest that protein translation via ribosomal translational machinery is reduced upon exposure to LSSMG, a phenomenon that has been indicated as a widespread response to microgravity, space, and Mars-like conditions not only in fungi (Sheehan et al., 2007;Willaert, 2013;Feger et al., 2016;Kamal et al., 2018Kamal et al., , 2019Blachowicz et al., 2019a). Remarkably, in our study, a decrease in translation and ribosome biogenesis was only observed in the wild type whole-cell proteome and, to a minor extent, in the mutant secretome ( Figure 5B). ...
... Also in the mutant, the upregulation of hydrolytic enzymes such as the alpha, alpha-trehalase suggests a recourse to store carbohydrates as a carbon source. By contrast, production of compounds that increase the osmotolerancy (e.g., trehalose) represents a quite common protective measure implemented by microorganisms under microgravity and other types of stress (Willaert, 2013). ...
Article
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... [298,211], environments with radiation (Section 13.2.9) [305], atmosphere/high altitude [160,[306][307][308][309], and last but not least, microgravity [310][311][312][313]. ...
... Authors concluded that their results show that microgravity imposes a stress condition that has the characteristics of an osmotic stress. Indeed, cellular energy is directed toward protective measures such as cell wall biosynthesis (cell wall integrity pathway activation) and the production of compounds (glycerol, trehalose) that increase the osmotolerance (high osmolarity glycerol pathway) [53]. ...
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One of the new challenges facing humanity is to reach increasingly further distant space targets. It is therefore of upmost importance to understand the behavior of microorganisms that will unavoidably reach the space environment together with the human body and equipment. Indeed, microorganisms could activate their stress defense mechanisms, modifying properties related to human pathogenesis. The host-microbe interactions, in fact, could be substantially affected under spaceflight conditions and the study of microorganisms' growth and activity is necessary for predicting these behaviors and assessing precautionary measures during spaceflight. This review gives an overview of the effects of microgravity and space radiation on microorganisms both in real and simulated conditions.
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