Advances in yeast preservation: physiological aspects for cell perpetuation

Physiological and genetic regulation of anhydrobiosis in yeast cells

Anhydrobiosis is a state of living organisms during which their metabolism is reversibly delayed or suspended due to a high degree of dehydration. Yeast cells, which are widely used in the food industry, may be induced into this state. The degree of viability of yeast cells undergoing the drying process also depends on rehydration. In an attempt to explain the essence of the state of anhydrobiosis and clarify the mechanisms responsible for its course, scientists have described various cellular compounds and structures that are responsible for it. The structures discussed in this work include the cell wall and plasma membrane, vacuoles, mitochondria, and lysosomes, among others, while the most important compounds include trehalose, glycogen, glutathione, and lipid droplets. Various proteins (Stf2p; Sip18p; Hsp12p and Hsp70p) and genes (STF2; Nsip18; TRX2; TPS1 and TPS2) are also responsible for the process of anhydrobiosis. Each factor has a specific function and is irreplaceable, detailed information is presented in this overview.

Mandacaru fruit pulp (Cereus jamacaru D.C.) as an adjunct and its influence on Beer properties

Beer is a complex product due to its raw materials (malt, hops, yeast, and water). Beer production can also use other matters as adjuncts. This study investigated the influence of Mandacaru fruit pulp (MFP) as an adjunct on volatile and phenolic compounds, and antioxidant properties of Beer. Worts were produced using four treatments including a control. Fermentations were conducted for 10 days at 18 °C using yeast Lachancea spp, maturated at 3 °C for 15 days, and bottled at 20 °C for 15 days. All compounds were evaluated by HPLC, and GC-MS. Worts' supplementation influenced the volatile and phenolic profile and increased the antioxidant activity of wort and Beer. Beers A (100 g of MFP/L), B (200 g of MFP/L), and C (300 g of MFP/L) presented higher ethanol and glycerol content. Beer C contained the highest antioxidant activity and total phenolic content. Worts' supplemented with MFP increased aroma formation.

Introduction to Bacterial Anhydrobiosis: A General Perspective and the Mechanisms of Desiccation-Associated Damage

Anhydrobiosis is the ability of selected organisms to lose almost all water and enter a state of reversible ametabolism. Such an organism dries up to a state of equilibrium with dry air. Unless special protective mechanisms exist, desiccation leads to damage, mainly to proteins, nucleic acids, and membrane lipids. A short historical outline of research on extreme dehydration of living organisms and the current state of research are presented. Terminological issues are outlined. The role of water in the cell and the mechanisms of damage occurring in the cell under the desiccation stress are briefly discussed. Particular attention was paid to damage to proteins, nucleic acids, and membrane lipids. Understanding the nature of the changes and damage associated with desiccation is essential for the study of desiccation-tolerance mechanisms and application research. Difficulties related to the definition of life and the limits of life in the scientific discussion, caused by the phenomenon of anhydrobiosis, were also indicated.

Microbial anhydrobiosis

The loss of cellular water (desiccation) and the resulting low cytosolic water activity are major stress factors for life. Numerous prokaryotic and eukaryotic taxa have evolved molecular and physiological adaptions to periods of low water availability or water-limited environments that occur across the terrestrial Earth. The changes within cells during the processes of desiccation and rehydration, from the activation (and inactivation) of biosynthetic pathways to the accumulation of compatible solutes, have been studied in considerable detail. However, relatively little is known on the metabolic status of organisms in the desiccated state; that is, in the sometimes extended periods between the drying and rewetting phases. During these periods, which can extend beyond decades and which we term 'anhydrobiosis', organismal survival could be dependent on a continued supply of energy to maintain the basal metabolic processes necessary for critical functions such as macromolecular repair. Here, we review the state of knowledge relating to the function of microorganisms during the anhydrobiotic state, highlighting substantial gaps in our understanding of qualitative and quantitative aspects of molecular and biochemical processes in desiccated cells.

Preservation of non-Saccharomyces yeasts: Current technologies and challenges

There is a recent and growing interest in the study and application of non-Saccharomyces yeasts, mainly in fermented foods. Numerous publications and patents show the importance of these yeasts. However, a fundamental issue in studying and applying them is to ensure an appropriate preservation scheme that allows to the non-Saccharomyces yeasts conserve their characteristics and fermentative capabilities by long periods of time. The main objective of this review is to present and analyze the techniques available to preserve these yeasts (by conventional and non-conventional methods), in small or large quantities for laboratory or industrial applications, respectively. Wine fermentation is one of the few industrial applications of non-Saccharomyces yeasts, but the preservation stage has been a major obstacle to achieve a wider application of these yeasts. This review considers the preservation techniques, and clearly defines parameters such as culturability, viability, vitality and robustness. Several conservation strategies published in research articles as well as patents are analyzed, and the advantages and disadvantages of each technique used are discussed. Another important issue during conservation processes is the stress to which yeasts are subjected at the time of preservation (mainly oxidative stress). There is little published information on the subject for non-Saccharomyces yeast, but it is a fundamental point to consider when designing a preservation strategy.

Anhydrobiosis in yeast: role of cortical endoplasmic reticulum protein Ist2 in Saccharomyces cerevisiae cells during dehydration and subsequent rehydration

Two Saccharomyces cerevisiae strains, BY4741 and BY4741-derived strain lacking the IST2 gene (ist2Δ), were used to characterise the possible role of cortical endoplasmic reticulum (ER) protein Ist2 upon cell dehydration and subsequent rehydration. For the first time, we show that not only protein components of the plasma membrane (PM), but also at least one ER membrane protein (Ist2) play an important role in the maintenance of the viability of yeast cells during dehydration and subsequent rehydration. The low viability of the mutant strain ist2∆ upon dehydration-rehydration stress was related to the lack of Ist2 protein in the ER. We revealed that the PM of ist2∆ strain is not able to completely restore its molecular organisation during reactivation from the state of anhydrobiosis. As the result, the permeability of the PM remains high regardless of the type of reactivation (rapid or gradual rehydration). We conclude that ER protein Ist2 plays an important role in ensuring the stability of molecular organisation and functionality of the PM during dehydration-rehydration stress. These results indicate an important role of ER-PM interactions during cells transition into the state of anhydrobiosis and the subsequent restoration of their physiological activities.

Changes in Energy Status of Saccharomyces cerevisiae Cells during Dehydration and Rehydration

Anhydrobiosis is the state of life when cells are exposed to waterless conditions and gradually cease their metabolism. In this study, we determined the sequence of events in Saccharomyces cerevisiae energy metabolism during processes of dehydration and rehydration. The intensities of respiration and acidification of the medium, the amounts of phenyldicarbaundecaborane (PCB⁻) bound to yeast membranes, and the capabilities of cells to accumulate K⁺ were assayed using an electrochemical monitoring system, and the intracellular content of ATP was measured using a bioluminescence assay. Mesophilic, semi-resistant to desiccation S. cerevisiae strain 14 and thermotolerant, very resistant to desiccation S. cerevisiae strain 77 cells were compared. After 22 h of drying, it was possible to restore the respiration activity of very resistant to desiccation strain 77 cells, especially when glucose was available. PCB⁻ binding also indicated considerably higher metabolic activity of dehydrated S. cerevisiae strain 77 cells. Electrochemical K⁺ content and medium acidification assays indicated that permeabilization of the plasma membrane in cells of both strains started almost simultaneously, after 8–10 h of desiccation, but semi-resistant strain 14 cells maintained the K⁺ gradient for longer and more strongly acidified the medium. For both cells, the fast rehydration in water was less efficient compared to reactivation in the growth medium, indicating the need for nutrients for the recovery. Higher viability of strain 77 cells after rehydration could be due to the higher stability of their mitochondria.