Yeast cells are well adapted to interfacial habitats, such as the surfaces of soil or plants, where they can resist frequent fluctuations between wet and dry conditions. Saccharomyces cerevisiae is ...recognized as an anhydrobiotic organism, and it has been the subject of numerous studies that aimed to elucidate this ability. Extensive data have been obtained from these studies based on a wide range of experimental approaches, which have added significantly to our understanding of the cellular bases and mechanisms of resistance to desiccation. The aim of this review is to provide an integrated view of these mechanisms in yeast and to describe the survival kit of S. cerevisiae for anhydrobiosis. This kit comprises constitutive and inducible mechanisms that prevent cell damage during dehydration and rehydration. This review also aims to characterize clearly the phenomenon of anhydrobiosis itself based on detailed descriptions of the causes and effects of the constraints imposed on cells by desiccation. These constraints mainly lead to mechanical, structural, and oxidative damage to cell components. Considerations of these constraints and the possible utilization of components of the survival kit could help to improve the survival of sensitive cells of interest during desiccation.
Yeasts are anhydrobiotes that accumulate large amounts of trehalose, which is involved in the vitrification of the cytoplasm during drastic desiccation. The effect of devitrification, which can be ...induced by the transient exposure of desiccated yeasts to increased humidity or elevated temperature, on the survival of yeast has been studied. A glass transition temperature (
T
g
)/water activity (
a
w
) diagram of yeast was constructed based on differential scanning calorimetry analysis. The survival rate of yeasts that were equilibrated at different relative humidities (RHs) and temperature values over their
T
g
range was measured. The results revealed a long period of cell preservation at an intermediate RH (55%), with 100% survival observed after 3 months, a loss of 1.24 log colony-forming units/g recorded after 1 year at 25 °C and full preservation of viability at 75 °C for 60 min and at 100 °C and 12% RH for up to 10 min. These findings led us to conclude that dried yeast can resist low or intermediate RH values and elevated temperatures in the devitrified state. Considering the thermal and humidity fluctuations occurring in the yeast environments, we hypothesized that the supercooled state, which occurs immediately above the
T
g
after rehydration or heating, is a protective state that is involved in the persistence of yeasts at intermediate humidity levels.
Key points
•
Yeast survival for months in a supercooled state is observed at room temperature.
•
Dried yeasts survive a 10-min exposure to 100 °C in the supercooled state.
•
The supercooled state is suitable for yeast preservation.
The objective of this study was to evaluate the performance of
Lactobacillus acidophilus
cells as a novel encapsulating carrier for fisetin via osmoporation. Initially, the effects of osmotic ...pressure and initial fisetin concentration on the performance of the osmoporation process were evaluated. The best results were achieved when 15 MPa was applied, while the maximum loading capacity was reached when fisetin concentration of 2.0 mg·mL
−1
was used. For these conditions, the cell viability, encapsulation efficiency (EE), and encapsulated fisetin content (EF) were 72%, 28%, and 0.990 mg, respectively. Further, the encapsulation was confirmed by Fourier transform-infrared (FT-IR), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) analysis. DSC thermograms revealed an increase of 40 °C in the melting point of fisetin after encapsulation. In addition, the enhancement of fisetin bioaccessibility by osmoporated biocapsules is shown for the first time in the literature. When the fisetin biocapsules were subjected to in vitro gastrointestinal digestion, 99.6% of the encapsulated content were retained through the gastric stage and 45.5% were released during the intestinal stage, despite no active cells were detected during simulated digestion. These results suggest that alive cells are required for an effective osmoporation-assisted encapsulation process; however, osmoporated biocapsules can efficiently protect and preserve labile compounds, independently of their activity. Overall, this study demonstrated that osmoporation using probiotic
L. acidophilus
is a simple, versatile, and efficient technique to encapsulate and deliver lipophilic fisetin for food applications.
Key points
•Fisetin is efficiently encapsulated into L. acidophilus via osmoporation.
•Fisetin bioaccessibility is improved by osmoporation into L. acidophilus.
•Release mechanisms of osmoporation carriers are independent of the cell activity.
Microbial food spoilage is an important cause of health and economic issues and can occur via resilient contamination of food surfaces. Novel technologies, such as the use of visible light, have seen ...the light of day to overcome the drawbacks associated with surface disinfection treatments. However, most studies report that photo-inactivation of microorganisms with visible light requires long time treatments. In the present study, a novel light electroluminescent diode (LED)-based device was designed to generate irradiation at an ultra-high power density (901.1 mW/cm
2
). The efficacy of this technology was investigated with the inactivation of the yeast
S. cerevisiae
. Short-time treatments (below 10 min) at 405 nm induced a ~4.5 log reduction rate of the cultivable yeast population. The rate of inactivation was positively correlated to the overall energy received by the sample and, at a similar energy, to the power density dispatched by the lamp. A successful disinfection of several food contact surfaces (stainless steel, glass, polypropylene, polyethylene) was achieved as
S. cerevisiae
was completely inactivated within 5 min of treatments. The disinfection of stainless steel was particularly effective with a complete inactivation of the yeast after 2 min of treatment. This ultra-high irradiance technology could represent a novel cost- and time-effective candidate for microbial inactivation of food surfaces. These treatments could see applications beyond the food industry, in segments such as healthcare or public transport.
Key points
•
A novel LED-based device was designed to emit ultra-high irradiance blue light
•
Short time treatments induced high rate of inhibition of S. cerevisiae
•
Multiple food contact surfaces were entirely disinfected with 5-min treatments
The plasma membrane (PM) is a main site of injury during osmotic perturbation. Sterols, major lipids of the PM structure in eukaryotes, are thought to play a role in ensuring the stability of the ...lipid bilayer during physicochemical perturbations. Here, we investigated the relationship between the nature of PM sterols and resistance of the yeast Saccharomyces cerevisiae to hyperosmotic treatment. We compared the responses to osmotic dehydration (viability, sterol quantification, ultrastructure, cell volume, and membrane permeability) in the wild-type (WT) strain and the ergosterol mutant erg6Δ strain. Our main results suggest that the nature of membrane sterols governs the mechanical behavior of the PM during hyperosmotic perturbation. The mutant strain, which accumulates ergosterol precursors, was more sensitive to osmotic fluctuations than the WT, which accumulates ergosterol. The hypersensitivity of erg6Δ was linked to modifications of the membrane properties, such as stretching resistance and deformation, which led to PM permeabilization during the volume variation during the dehydration–rehydration cycles. Anaerobic growth of erg6Δ strain with ergosterol supplementation restored resistance to osmotic treatment. These results suggest a relationship between hydric stress resistance and the nature of PM sterols. We discuss this relationship in the context of the evolution of the ergosterol biosynthetic pathway.
► Yeast mutant in sterol synthetic pathway (erg6Δ) is sensitive to hydric stress. ► Sterol nature affects plasma membrane integrity during hydric perturbation. ► Sterol structure influences plasma membrane deformation and resistance to stretching. ► Ergosterol complementation restores osmotic resistance in a sensitive mutant (erg6Δ). ► Ergosterol is involved in survival of wild-type yeast during hydric fluctuations.
Stabilization of freeze-dried lactic acid bacteria during long-term storage is challenging for the food industry. Water activity of the lyophilizates is clearly related to the water availability and ...maintaining a low a
during storage allows to increase bacteria viability. The aim of this study was to achieve a low water activity after freeze-drying and subsequently during long-term storage through the design of a lyoprotectant. Indeed, for the same water content as sucrose (commonly used lyoprotectant), water activity is lower for some components such as whey, micellar casein or inulin. We hypothesized that the addition of these components in a lyoprotectant, with a higher bound water content than sucrose would improve lactobacilli strains survival to long-term storage. Therefore, in this study, 5% whey (w/v), 5% micellar casein (w/v) or 5% inulin (w/v) were added to a 5% sucrose solution (w/v) and compared with a lyoprotectant only composed of 5% sucrose (w/v). Protective effect of the four lyoprotectants was assessed measuring Lactiplantibacillus plantarum CNCM I-4459 survival and water activity after freeze-drying and during 9 months storage at 25 °C.
The addition whey and inulin were not effective in increasing Lactiplantibacillus plantarum CNCM I-4459 survival to long-term-storage (4 log reduction at 9 months storage). However, the addition of micellar casein to sucrose increased drastically the protective effect of the lyoprotectant (3.6 log i.e. 0.4 log reduction at 9 months storage). Comparing to a lyoprotectant containing whey or inulin, a lyoprotectant containing micellar casein resulted in a lower water activity after freeze-drying and its maintenance during storage (0.13 ± 0.05).
The addition of micellar casein to a sucrose solution, contrary to the addition of whey and inulin, resulted in a higher bacterial viability to long-term storage. Indeed, for the same water content as the others lyoprotectants, a significant lower water activity was obtained with micellar casein during storage. Probably due to high bound water content of micellar casein, less water could be available for chemical degradation reactions, responsible for bacterial damages during long-term storage. Therefore, the addition of this component to a sucrose solution could be an effective strategy for dried bacteria stabilization during long-term storage.
Probiotic microorganisms have historically been used to rebalance disturbed intestinal microbiota and to diminish gastrointestinal disorders, such as diarrhea or inflammatory bowel diseases (e.g., ...Crohn's disease and ulcerative colitis). Recent studies explore the potential for expanded uses of probiotics on medical disorders that increase the risk of developing cardiovascular diseases and diabetes, such as obesity, hypercholesterolemia, arterial hypertension, and metabolic disturbances such as hyperhomocysteinemia and oxidative stress. This review aims at summarizing the proposed molecular and cellular mechanisms involved in probiotic–host interactions and to identify the nature of the resulting beneficial effects. Specific probiotic strains can act by modulating immune response, by producing particular molecules or releasing biopeptides, and by modulating nervous system activity. To date, the majority of studies have been conducted in animal models. New investigations on the related mechanisms in humans need to be carried out to better enable targeted and effective use of the broad variety of probiotic strains.
The promising next-generation probiotic Faecalibacterium prausnitzii is one of the most abundant acetate-consuming, butyrate-producing bacteria in the healthy human gut. Yet, little is known about ...how acetate availability affects this bacterium's gene expression strategies. Here, we investigated the effect of acetate on temporal changes in the transcriptome of F. duncaniae A2-165 cultures using RNA sequencing. We compared gene expression patterns between two growth phases (early stationary vs. late exponential) and two acetate levels (low: 3 mM vs. high: 23 mM). Only in low-acetate conditions, a general stress response was activated. In high-acetate conditions, there was greater expression of genes related to butyrate synthesis and to the importation of B vitamins and iron. Specifically, expression was strongly activated in the case of the feoAABC operon, which encodes a FeoB ferrous iron transporter, but not in the case of the feoAB gene, which encodes a second putative FeoAB transporter. Moreover, excess ferrous iron repressed feoB expression but not feoAB. Lastly, FeoB but not FeoAB peptides from strain A2-165 were found in abundance in a healthy human fecal metaproteome. In conclusion, we characterized two early-stationary transcriptomes based on acetate consumption and this work highlights the regulation of feoB expression in F. duncaniae A2-165.
Relative air humidity fluctuations could potentially affect the development and persistence of pathogenic microorganisms in their environments. This study aimed to characterize the impact of relative ...air humidity (RH) variations on the survival of Listeria monocytogenes, a bacterium persisting on food processing plant surfaces. To assess conditions leading to the lowest survival rate, four strains of L. monocytogenes (EGDe, CCL500, CCL128, and LO28) were exposed to different RH conditions (75%, 68%, 43% and 11%) with different drying kinetics and then rehydrated either progressively or instantaneously. The main factors that affected the survival of L. monocytogenes were RH level and rehydration kinetics. Lowest survival rates between 1% and 0.001% were obtained after 3 hours of treatment under optimal conditions (68% RH and instantaneous rehydration). The survival rate was decreased under 0.001% after prolonged exposure (16h) of cells under optimal conditions. Application of two successive dehydration and rehydration cycles led to an additional decrease in survival rate. This preliminary study, performed in model conditions with L. monocytogenes, showed that controlled ambient RH fluctuations could offer new possibilities to control foodborne pathogens in food processing environments and improve food safety.
In this study, we investigated the kinetic and the magnitude of dehydrations on yeast plasma membrane (PM) modifications because this parameter is crucial to cell survival. Functional (permeability) ...and structural (morphology, ultrastructure, and distribution of the protein Sur7-GFP contained in sterol-rich membrane microdomains) PM modifications were investigated by confocal and electron microscopy after progressive (non-lethal) and rapid (lethal) hyperosmotic perturbations. Rapid cell dehydration induced the formation of many PM invaginations followed by membrane internalization of low sterol content PM regions with time. Permeabilization of the plasma membrane occurred during the rehydration stage because of inadequacies in the membrane surface and led to cell death. Progressive dehydration conducted to the formation of some big PM pleats without membrane internalization. It also led to the modification of the distribution of the Sur7-GFP microdomains, suggesting that a lateral rearrangement of membrane components occurred. This event is a function of time and is involved in the particular deformations of the PM during a progressive perturbation. The maintenance of the repartition of the microdomains during rapid perturbations consolidates this assumption. These findings highlight that the perturbation kinetic influences the evolution of the PM organization and indicate the crucial role of PM lateral reorganization in cell survival to hydric perturbations.
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