Protective Effects of Melatonin on Saccharomyces cerevisiae under Ethanol Stress

New insight into protective effect against oxidative stress and biosynthesis of exopolysaccharides produced by Lacticaseibacillus paracasei NC4 from fermented eggplant

Fermented eggplant is a traditional fermented food, however lactic acid bacteria capable of producing exopolysaccharide (EPS) have not yet been exploited. The present study focused on the production and protective effects against oxidative stress of an EPS produced by Lacticaseibacillus paracasei NC4 (NC4-EPS), in addition to deciphering its genomic features and EPS biosynthesis pathway. Among 54 isolates tested, strain NC4 showed the highest EPS yield and antioxidant activity. The maximum EPS production (2.04 ± 0.11 g/L) was achieved by culturing in MRS medium containing 60 g/L sucrose at 37 °C for 48 h. Under 2 mM H2O2 stress, the survival of a yeast model Saccharomyces cerevisiae treated with 0.4 mg/mL NC4-EPS was 2.4-fold better than non-treated cells, which was in agreement with the catalase and superoxide dismutase activities measured from cell lysates. The complete genome of NC4 composed of a circular chromosome of 2,888,896 bp and 3 circular plasmids. The NC4 genome comprises more genes with annotated function in nitrogen metabolism, phosphorus metabolism, cell division and cell cycle, and iron acquisition and metabolism as compared to other reported L. paracasei. Of note, the eps gene cluster is not conserved across L. paracasei. Pathways of sugar metabolism for EPS biosynthesis were proposed for the first time, in which gdp pathway only present in few plant-derived bacteria was identified. These findings shed new light on the cell-protective activity and biosynthesis of EPS produced by L. paracasei, paving the way for future efforts to enhance yield and tailor-made EPS production for food and pharmaceutical industries.

A consortium of different Saccharomyces species enhances the content of bioactive tryptophan-derived compounds in wine fermentations

In recent years, the presence of molecules derived from aromatic amino acids in wines has been increasingly demonstrated to have a significant influence on wine quality and stability. In addition, interactions between different yeast species have been observed to influence these final properties. In this study, a screening of 81 yeast strains from different environments was carried out to establish a consortium that would promote the improvement of indolic compound levels in wine. Two strains, Saccharomyces uvarum and Saccharomyces eubayanus, with robust fermentative capacity were selected to be combined with a Saccharomyces cerevisiae strain with a predisposition towards the production of indolic compounds. Fermentation dynamics were studied in pure cultures, co-inoculations and sequential inoculations, analysing strain interactions and end-of-fermentation characteristics. Fermentations showing significant interactions were further analyzed for the resulting indolic compounds and aroma profile, with the aim of observing potential interactions and synergies resulting from the combination of different strains in the final wine. Sequential inoculation of S. cerevisiae after S. uvarum or S. eubayanus was observed to increase indolic compound levels, particularly serotonin and 3-indoleacetic acid. This study is the first to demonstrate how the formation of microbial consortia can serve as a useful strategy to enhance compounds with interesting properties in wine, paving the way for future studies and combinations.

Plant-derived antioxidant dipeptides provide lager yeast with osmotic stress tolerance for very high gravity fermentation

Osmotic stress in the yeast limits productivity in industrial beer production under very high gravity brewing. This study focused on assessing the protective impacts of eleven plant-derived antioxidant dipeptides (PADs) on the osmotic stress tolerance of lager yeast. The results showed that PADs provided yeast with stress tolerance under osmotic stress. PADs supplementation enhanced cell membrane integrity and reduced oxidative damage. PADs upregulated the expression of SOD2, PEX11 and CTT1 genes under osmotic stress. Moreover, the volatile compounds contents and antioxidant activities of beers were improved by PADs, suggesting favorable quality characteristics. Especially, Phe-Cys and Leu-His could increase the DPPH radical scavenging activity of beer by 41.92% and 18.78% respectively, compared with control. Therefore, PADs are industrially scalable enhancers to improve the ability of yeast to resist osmotic stress and beer quality during very high gravity brewing.

Cellular Stress Impact on Yeast Activity in Biotechnological Processes-A Short Overview

The importance of Saccharomyces cerevisiae yeast cells is known worldwide, as they are the most used microorganisms in biotechnology for bioethanol and biofuel production. Also, they are analyzed and studied for their similar internal biochemical processes to human cells, for a better understanding of cell aging and response to cell stressors. The special ability of S. cerevisiae cells to develop in both aerobic and anaerobic conditions makes this microorganism a viable model to study the transformations and the way in which cellular metabolism is directed to face the stress conditions due to environmental changes. Thus, this review will emphasize the effects of oxidative, ethanol, and osmotic stress and also the physiological and genetic response of stress mitigation in yeast cells.

Bioactive dipeptides enhance the tolerance of lager yeast to ethanol-oxidation cross-stress by regulating the multilevel defense system

Although high gravity brewing technology has been widely used for beer industries due to its economic benefits, yeast cells are subjected to multiple environmental stresses throughout the fermentation process. Eleven bioactive dipeptides (LH, HH, AY, LY, IY, AH, PW, TY, HL, VY, FC) were selected to evaluate their effects on cell proliferation, cell membrane defense system, antioxidant defense system and intracellular protective agents of lager yeast against ethanol-oxidation cross-stress. Results showed that the multiple stresses tolerance and fermentation performance of lager yeast were enhanced by bioactive dipeptides. Cell membrane integrity was improved by bioactive dipeptides through altering the structure of macromolecular compounds of the cell membrane. Intracellular reactive oxygen species (ROS) accumulation was significantly decreased by bioactive dipeptides, especially for FC, decreasing by 33.1%, compared with the control. The decrease of ROS was closely related to the increase of mitochondrial membrane potential, intracellular antioxidant enzyme activities including superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), and glycerol level. In addition, bioactive dipeptides could regulate the expression of key genes (GPD1, OLE1, SOD2, PEX11, CTT1, HSP12) to enhance the multilevel defense systems under ethanol-oxidation cross-stress. Therefore, bioactive dipeptides should be potentially efficient and feasible bioactive ingredients to improve the multiple stresses tolerance of lager yeast during high gravity fermentation.

Involvement of the High-Osmolarity Glycerol Pathway of Saccharomyces Cerevisiae in Protection against Copper Toxicity

Although essential for life, copper is also potentially toxic in concentrations that surpass physiological thresholds. The high-osmolarity glycerol pathway of yeast is the main regulator of adaptive responses and is known to play crucial roles in the responses to various stressors. The objective of this research is to determine whether the HOG pathway could be activated and to investigate the possible interplay of the HOG pathway and oxidative stress due to copper exposure. In this research, we demonstrate that copper could induce oxidative stress, including the elevated concentrations of reactive oxygen species (ROS) and malondialdehyde (MDA). Increased combination with GSH, increased intracellular SOD activity, and the up-regulation of relevant genes can help cells defend themselves against oxidative toxicity. The results show that copper treatment triggers marked and prolonged Hog1 phosphorylation. Significantly, oxidative stress generated by copper toxicity is essential for the activation of Hog1. Activated Hog1 is translocated to the nucleus to regulate the expressions of genes such as CTT1, GPD1, and HSP12, among others. Furthermore, copper exposure induced significant G1-phase cell cycle arrest, while Hog1 partially participated in the regulation of cell cycle progression. These novel findings reveal another role for Hog1 in the regulation of copper-induced cellular stress.