Disruption of ergosterol and tryptophan biosynthesis, as well as cell wall integrity pathway and the intracellular pH homeostasis, lead to mono-(2-ethylhexyl)-phthalate toxicity in budding yeast

Disruption of phosphate metabolism and sterol transport-related genes conferring yeast resistance to vanillin and rapid ethanol production

Vanillin is a potent growth-inhibiting factor in Saccharomyces cerevisiae during lignocellulose biorefineries. Here, a haploid gene-deletion library was screened to search for vanillin-tolerant mutants and explain the possible tolerance mechanisms. Twenty-two deletion mutants were identified. The deleted genes in these mutants were involved in phosphate and inositol polyphosphate metabolism and intracellular sterol transport. Activation of the phosphate signaling pathway is not conducive to yeast against the pressure of vanillin. Furthermore, the findings indicate the role of inositol polyphosphates in altering vanillin tolerance by regulating phosphate metabolism. Meanwhile, reducing the transport of sterols from the plasma membrane enhanced tolerance to vanillin. In the presence of vanillin, the representative yeast deletions, pho84Δ and lam3Δ, showed good growth performance and promoted rapid ethanol production. Overall, this study identifies robust yeast strain alternatives for ethanol fermentation of cellulose and provides guidance for further genomic reconstruction of yeast strains.

Deletion of Atg22 gene contributes to reduce programmed cell death induced by acetic acid stress in Saccharomyces cerevisiae

BACKGROUND

Programmed cell death (PCD) induced by acetic acid, the main by-product released during cellulosic hydrolysis, cast a cloud over lignocellulosic biofuel fermented by Saccharomyces cerevisiae and became a burning problem. Atg22p, an ignored integral membrane protein located in vacuole belongs to autophagy-related genes family; prior study recently reported that it is required for autophagic degradation and efflux of amino acids from vacuole to cytoplasm. It may alleviate the intracellular starvation of nutrition caused by Ac and increase cell tolerance. Therefore, we investigate the role of atg22 in cell death process induced by Ac in which attempt is made to discover new perspectives for better understanding of the mechanisms behind tolerance and more robust industrial strain construction.

RESULTS

In this study, we compared cell growth, physiological changes in the absence and presence of Atg22p under Ac exposure conditions. It is observed that disruption and overexpression of Atg22p delays and enhances acetic acid-induced PCD, respectively. The deletion of Atg22p in S. cerevisiae maintains cell wall integrity, and protects cytomembrane integrity, fluidity and permeability upon Ac stress by changing cytomembrane phospholipids, sterols and fatty acids. More interestingly, atg22 deletion increases intracellular amino acids to aid yeast cells for tackling amino acid starvation and intracellular acidification. Further, atg22 deletion upregulates series of stress response genes expression such as heat shock protein family, cell wall integrity and autophagy.

CONCLUSIONS

The findings show that Atg22p possessed the new function related to cell resistance to Ac. This may help us have a deeper understanding of PCD induced by Ac and provide a new strategy to improve Ac resistance in designing industrial yeast strains for bioethanol production during lignocellulosic biofuel fermentation.

Chemical-genetic interaction landscape of mono-(2-ethylhexyl)-phthalate using chemogenomic profiling in yeast

Integration of chemical-genetic interaction data with biological functions provides a mechanistic understanding of how toxic compounds affect cells. Mono-(2-ethylhexyl)-phthalate (MEHP) is an active metabolite of di-(2-ethylhexyl)-phthalate (DEHP), a commonly used plasticizer. MEHP adversely affects human health causing hepatotoxicity and reproductive toxicity. How MEHP affects cellular physiology is not fully understood. We utilized a genome-wide competitive fitness-based assay called 'chemogenomic profiling' to determine the genetic interaction map of MEHP in Saccharomyces cerevisiae. Gene Ontology enrichment analysis of 218 genes that provide resistance to MEHP indicated that MEHP affects seven cellular processes namely: (1) cellular amino acid biosynthetic process, (2) sterol biosynthetic process, (3) cellular transport, (4) transcriptional and translational regulation, (5) protein glycosylation, (6) cytokinesis and cell morphogenesis and (7) ionic homeostasis. We show that MEHP protects yeast cells from membrane perturbing agents such as amphotericin B, dihydrosphingosine and phytosphingosine. Moreover, we also demonstrate that MEHP compromises the integrity of the yeast plasma membrane and cell wall. Our work provides a basis for further investigation of MEHP toxicity in humans.

The Effects of Mono-(2-Ethylhexyl) Phthalate (MEHP) on Human Estrogen Receptor (hER) and Androgen Receptor (hAR) by YES/YAS In Vitro Assay

Endocrine active compounds with structural similarities to natural hormones such as 17β-estradiol (E2) and androgen are suspected to affect the human endocrine system by inducing hormone-dependent effects. This study aimed to detect the (anti-)estrogenic and (anti-)androgenic activities of mono-(2-ethylhexyl) phthalate (MEHP) by yeast estrogen/androgen bioassay (YES/YAS). In addition, the mechanism and uptake of MEHP to receptors during agonistic and antagonistic activities were investigated through the activation signal recovery test and chromatographic analysis using liquid chromatography and tandem mass spectrometry (LC-MS/MS). Estrogenic and androgenic activities of MEHP were not observed. However, MEHP exhibited anti-estrogenic (IC₅₀ = 125 μM) and anti-androgenic effects (IC₅₀ = 736 μM). It was confirmed that these inhibitory effects of MEHP were caused by receptor-mediated activity of the estrogen receptor and non-receptor-mediated activity of the androgen receptor in an activation signal recovery test. When IC₅₀ concentrations of anti-estrogenic and androgenic activity of MEHP were exposed to yeast cells, the uptake concentration observed was 0.0562 ± 0.0252 μM and 0.143 ± 0.0486 μM by LC-MS/MS analysis.

The protein kinase Cmk2 negatively regulates the calcium/calcineurin signalling pathway and expression of calcium pump genes PMR1 and PMC1 in budding yeast

Through a genome-wide screen we have identified calcium-tolerant deletion mutants for five genes in the budding yeast Saccharomyces cerevisiae. In addition to CNB1 and RCN1 that are known to play a role in the calcium signalling pathway, the protein kinase gene CMK2, the sphingolipid homeostasis-related gene ORM2 and the gene SIF2 encoding the WD40 repeat-containing subunit of Set3C histone deacetylase complex are involved in the calcium sensitivity of yeast cells to extracellular calcium. Cmk2 and the transcription factor Crz1 have opposite functions in the response of yeast cells to calcium stress. Deletion of CMK2 elevates the level of calcium/calcineurin signalling and increases the expression level of PMR1 and PMC1, which is dependent on Crz1. Effects of Cmk2 on calcium sensitivity and calcium/calcineurin signalling are dependent on its kinase activity. Therefore, Cmk2 is a negative feedback controller of the calcium/calcineurin signalling pathway. Furthermore, the cmk2 crz1 double deletion mutant is more resistant than the crz1 deletion mutant, suggesting that Cmk2 has an additional Crz1-independent role in promoting calcium tolerance.