Response of Saccharomyces cerevisiae to the stimulation of lipopolysaccharide

A Systematic Survey of Characteristic Features of Yeast Cell Death Triggered by External Factors

Cell death in response to distinct stimuli can manifest different morphological traits. It also depends on various cell death signaling pathways, extensively characterized in higher eukaryotes but less so in microorganisms. The study of cell death in yeast, and specifically Saccharomyces cerevisiae, can potentially be productive for understanding cell death, since numerous killing stimuli have been characterized for this organism. Here, we systematized the literature on external treatments that kill yeast, and which contains at least minimal data on cell death mechanisms. Data from 707 papers from the 7000 obtained using keyword searches were used to create a reference table for filtering types of cell death according to commonly assayed parameters. This table provides a resource for orientation within the literature; however, it also highlights that the common view of similarity between non-necrotic death in yeast and apoptosis in mammals has not provided sufficient progress to create a clear classification of cell death types. Differences in experimental setups also prevent direct comparison between different stimuli. Thus, side-by-side comparisons of various cell death-inducing stimuli under comparable conditions using existing and novel markers that can differentiate between types of cell death seem like a promising direction for future studies.

S. boulardii Fails to Hold Its Cell Wall Integrity against Nonpathogenic E. coli: Are Probiotic Yeasts Losing the Battle?

Probiotic yeast Saccharomyces boulardii exerts direct probiotic action on pathogenic E. coli by trapping them on surfaces and inactivating toxic lipopolysaccharides. Using optical dark-field microscopy, we show that nonpathogenic E. coli cells also readily bind probiotic S. boulardii. More importantly, the adhered nonpathogenic E. coli progressively damage S. boulardii cell walls and lyse them. Co-cultured methylene blue-supplemented agar-plate assay indicates that rough lipopolysaccharides might be playing a key role in S. boulardii cell wall damage. When experiments are repeated with lipopolysaccharide-depleted E. coli and also lipopolysaccharide-deficient E. coli, adhesion decreases substantially. The co-cultured assay further reveals that free lipopolysaccharides, released from E. coli, are also causing damage to S. boulardii walls like adhered E. coli. These new findings contradict the known S. boulardii-E. coli interaction mechanisms. We confirm that E. coli cells do not bind or damage human erythrocyte cell walls; therefore, they have not developed pathogenicity. The combined results demonstrate the first example of nonpathogenic E. coli being harmful to probiotic yeast S. boulardii. This finding is important because gut microbial flora contain large numbers of nonpathogenic E. coli. If they bind or damage probiotic S. boulardii cell walls, then the probiotic efficiency toward pathogenic E. coli will be compromised.

Nitrate and Phosphate Transporters Rescue Fluoride Toxicity in Yeast

Organisms are exposed to fluoride in the air, water, and soil. Yeast and other microbes utilize fluoride channels as a method to prevent intracellular fluoride accumulation and mediate fluoride toxicity. Consequently, deletion of fluoride exporter genes (FEX) in S. cerevisiae resulted in over 1000-fold increased fluoride sensitivity. We used this FEX knockout strain to identify genes, that when overexpressed, are able to partially relieve the toxicity of fluoride exposure. Overexpression of five genes, SSU1, YHB1, IPP1, PHO87, and PHO90, increase fluoride tolerance by 2- to 10-fold. Overexpression of these genes did not provide improved fluoride resistance in wild-type yeast, suggesting that the mechanism is specific to low fluoride toxicity in yeast. Ssu1p and Yhb1p both function in nitrosative stress response, which is induced upon fluoride exposure along with metal influx. Ipp1p, Pho87p, and Pho90p increase intracellular orthophosphate. Consistent with this observation, fluoride toxicity is also partially mitigated by the addition of high levels of phosphate to the growth media. Fluoride inhibits phosphate import upon stress induction and causes nutrient starvation and organelle disruption, as supported by gene induction monitored through RNA-Seq. The combination of observations suggests that transmembrane nutrient transporters are among the most sensitized proteins during fluoride-instigated stress.

Peptide (Lys-Leu) and amino acids (Lys and Leu) supplementations improve physiological activity and fermentation performance of brewer's yeast during very high-gravity (VHG) wort fermentation

Lys and Leu were generally considered as the key amino acids for brewer's yeast during beer brewing. In the present study, peptide Lys-Leu and a free amino acid (FAA) mixture of Lys and Leu (Lys + Leu) were supplemented in 24 °P wort to examine their effects on physiological activity and fermentation performance of brewer's yeast during very high-gravity (VHG) wort fermentation. Results showed that although both peptide Lys-Leu and their FAA mixture supplementations could increase the growth and viability, intracellular trehalose and glycerol content, wort fermentability, and ethanol content for brewer's yeast during VHG wort fermentation, and peptide was better than their FAA mixture at promoting growth and fermentation for brewer's yeast when the same dose was kept. Moreover, peptide Lys-Leu supplementation significantly increased the assimilation of Asp, but decreased the assimilation of Gly, Ala, Val, (Cys)2, Ile, Leu, Tyr, Phe, Lys, Arg, and Pro. However, the FAA mixture supplementation only promoted the assimilation of Lys and Leu, while reduced the absorption of total amino acids to a greater extent. Thus, the peptide Lys-Leu was more effective than their FAA mixture on the improvement of physiological activity, fermentation performance, and nitrogen metabolism of brewer's yeast during VHG wort fermentation.

Reactive oxygen species and Ca2+ are involved in cadmium-induced cell killing in yeast cells

Cadmium (Cd) is one of the most toxic heavy metals. It is of great environmental concern and its toxicity has been investigated in a variety of cells. In this study, we elucidated the toxic effects of Cd in cells of yeast (Saccharomyces cerevisiae). Our results showed that Cd²⁺ (0.05-5.0 mmol·L^-1) significantly inhibited yeast cell growth, and the inhibitory effect was positively correlated with Cd²⁺ concentrations. Cd²⁺ caused loss of yeast cell viability in a concentration- and duration-dependent manner. Intracellular reactive oxygen species (ROS) and Ca²⁺ levels increased in yeast cells after exposure to 5.0 mmol·L^-1 Cd for 6 h. Cd²⁺-caused cell viability loss was blocked by antioxidants (0.5 mmol·L^-1 ascorbic acid or 500 U·mL^-1 catalase) or Ca²⁺ antagonists (0.5 mmol·L^-1 ethylene glycol tetraacetic acid or 0.5 mmol·L^-1 LaCl₃). Moreover, a collapse of mitochondrial membrane potential (ΔΨ_m) was observed in Cd²⁺-treated yeast cells. These results indicate that Cd-induced yeast cell killing was associated with the elevation of intracellular ROS and Ca²⁺ levels and also the loss of ΔΨ_m.

Screening for anti-inflammatory components from Corydalis bungeana Turcz. based on macrophage binding combined with HPLC

Background

Corydalis bungeana Turcz. (CB; family: Corydalis DC.) is an anti-inflammatory medicinal herb used widely in traditional Chinese medicine (TCM) for upper respiratory tract infection, etc., but its anti-inflammatory active molecules are unknown. This study was designed to screen for the anti-inflammatory components from CB based on macrophage binding combined with HPLC.

Methods

Xylene-induced ear edema in mouse and carrageenan-induced hind-paw edema in rats were used to evaluate the anti-inflammatory activity of CB. The macrophage binding with high-performance liquid chromatography (HPLC) analysis and HPLC-MS were established to screen the potential active compounds. ELISA kits were performed to measure the levels of IL-6, IL-10, TNF-α and NO in RAW 264.7 macrophages culture media.

Results

The alkaloid extract of CB could inhibit significantly xylene-induced ear edema in mouse and carrageenan-induced hind-paw edema in rats. Two components binded to RAW 264.7 cell were identified as 12-hydroxycorynoline and corynoline. Bioassays demonstrated that these two compounds significantly inhibited LPS-induced IL-6, IL-10, TNF-α and NO levels.

Conclusions

The results suggest that corynoline and 12-hydroxycorynoline contribute to the anti-inflammatory effects of the alkaloid extract of CB. Our findings suggest that these two compounds can be used as candidate for anti-inflammatory drugs.