Regulation of Ergosterol Biosynthesis in Saccharomyces cerevisiae

Deletion of PMP3 increases ketoconazole resistance by affecting plasma membrane potential in Candida albicans

Ketoconazole is a classical antifungal drug commonly used in the clinic. With the increased use of ketoconazole in recent years, an increasing number of drug-resistant strains have emerged during clinical treatment. It is well known that fungi acquire drug resistance in multiple ways, while the molecular mechanisms underlying ketoconazole resistance remain for comprehensive exploration. In this study, we found that the expression of the small plasma membrane protein-encoding gene PMP3 was significantly down-regulated in several clinically isolated ketoconazole-resistant strains, indicating the relationship between PMP3 expression and ketoconazole resistance. By knocking out the PMP3, we found that the absence of the Pmp3 resulted in a significant increase in resistance of Candida albicans to ketoconazole, which was also confirmed in a systemic infection model in mice. We further demonstrated that various physiological properties, such as cell membrane fluidity, plasma membrane potential, permeability and ergosterol distribution were altered in the pmp3Δ/Δ mutant, which is associated with the enhanced cellular resistance to ketoconazole. In addition, overexpression rather than deletion of PMP3 alters the hyphal development and biofilm formation capacity in C. albicans. This study reveals the contribution of Pmp3 to alteration of drug resistance in fungal pathogens, which may guide the development of novel antifungal strategies.

Novel yeast-based biosensor for environmental monitoring of tebuconazole

Due to increasing demand for high and stable crop production, human populations are highly dependent on pesticide use for growing and storing food. Environmental monitoring of these agrochemicals is therefore of utmost importance, because of their collateral effects on ecosystem and human health. Even though most current-use analytical methods achieve low detection limits, they require procedures that are too complex and costly for routine monitoring. As such, there has been an increased interest in biosensors as alternative or complementary tools to streamline detection and quantification of environmental contaminants. In this work, we developed a biosensor for environmental monitoring of tebuconazole (TEB), a common agrochemical fungicide. For that purpose, we engineered S. cerevisiae cells with a reporter gene downstream of specific promoters that are expressed after exposure to TEB and characterized the sensitivity and specificity of this model system. After optimization, we found that this easy-to-use biosensor consistently detects TEB at concentrations above 5 μg L-1 and does not respond to realistic environmental concentrations of other tested azoles, suggesting it is specific. We propose the use of this system as a complementary tool in environmental monitoring programs, namely, in high throughput scenarios requiring screening of numerous samples. KEY POINTS: • A yeast-based biosensor was developed for environmental monitoring of tebuconazole. •The biosensor offers a rapid and easy method for tebuconazole detection ≥ 5 μg L-1. •The biosensor is specific to tebuconazole at environmentally relevant concentrations.

Oxygen alters redox cofactor dynamics and induces metabolic shifts in Saccharomyces cerevisiae during alcoholic fermentation

Environmental conditions significantly impact the metabolism of Saccharomyces cerevisiae, a Crabtree-positive yeast that maintains a fermentative metabolism in high-sugar environments even in the presence of oxygen. Although the introduction of oxygen has been reported to induce alterations in yeast metabolism, knowledge of the mechanisms behind these metabolic adaptations in relation to redox cofactor metabolism and their implications in the context of wine fermentation remains limited. This study aimed to compare the intracellular redox cofactor levels, the cofactor ratios, and primary metabolite production in S. cerevisiae under aerobic and anaerobic conditions in synthetic grape juice. The molecular mechanisms underlying these metabolic differences were explored using a transcriptomic approach. Aerobic conditions resulted in an enhanced fermentation rate and biomass yield. Total NADP(H) levels were threefold higher during aerobiosis, while a decline in the total levels of NAD(H) was observed. However, there were stark differences in the ratio of NAD+/NADH between the treatments. Despite few changes in the differential expression of genes involved in redox cofactor metabolism, anaerobiosis resulted in an increased expression of genes involved in lipid biosynthesis pathways, while the presence of oxygen increased the expression of genes associated with thiamine, methionine, and sulfur metabolism. The production of fermentation by-products was linked with differences in the redox metabolism in each treatment. This study provides valuable insights that may help steer the production of metabolites of industrial interest during alcoholic fermentation (including winemaking) by using oxygen as a lever of redox metabolism.

High-level biosynthesis of enantiopure germacrene D in yeast

Germacrene D, a sesquiterpenoid compound found mainly in plant essential oils at a low level as (+) and/or (-) enantiomeric forms, is an ingredient for the fragrance industry, but a process for the sustainable supply of enantiopure germacrene D is not yet established. Here, we demonstrate metabolic engineering in yeast (Saccharomyces cerevisiae) achieving biosynthesis of enantiopure germacrene D at a high titer. To boost farnesyl pyrophosphate (FPP) flux for high-level germacrene D biosynthesis, a background yeast chassis (CENses5C) was developed by genomic integration of the expression cassettes for eight ergosterol pathway enzymes that sequentially converted acetyl-CoA to FPP and by replacing squalene synthase promoter with a copper-repressible promoter, which restricted FPP flux to the competing pathway. Galactose-induced expression of codon-optimized plant germacrene D synthases led to 13-30 fold higher titers of (+) or (-)-germacrene D in CENses5C than the parent strain CEN.PK2.1C. Furthermore, genomic integration of germacrene D synthases in GAL80, LPP1 and rDNA loci generated CENses8(+D) and CENses8(-D) strains, which produced 41.36 µg/ml and 728.87 µg/ml of (+) and (-)-germacrene D, respectively, without galactose supplementation. Moreover, coupling of mitochondrial citrate pool to the cytosolic acetyl-CoA, by expressing a codon-optimized ATP-citrate lyase of oleaginous yeast, resulted in 137.71 µg/ml and 815.81 µg/ml of (+) or (-)-germacrene D in CENses8(+D)* and CENses8(-D)* strains, which were 67-120 fold higher titers than in CEN.PK2.1C. In fed-batch fermentation, CENses8(+D)* and CENses8(-D)* produced 290.28 µg/ml and 2519.46 µg/ml (+) and (-)-germacrene D, respectively, the highest titers in shake-flask fermentation achieved so far. KEY POINTS: • Engineered S. cerevisiae produced enantiopure (+) and (-)-germacrene D at high titers • Engineered strain produced up to 120-fold higher germacrene D than the parental strain • Highest titers of enantiopure (+) and (-)-germacrene D achieved so far in shake-flask.

Herbicides as fungicides: Targeting heme biosynthesis in the maize pathogen Ustilago maydis

Pathogens must efficiently acquire nutrients from host tissue to proliferate, and strategies to block pathogen access therefore hold promise for disease control. In this study, we investigated whether heme biosynthesis is an effective target for ablating the virulence of the phytopathogenic fungus Ustilago maydis on maize plants. We first constructed conditional heme auxotrophs of the fungus by placing the heme biosynthesis gene hem12 encoding uroporphyrinogen decarboxylase (Urod) under the control of nitrogen or carbon source-regulated promoters. These strains were heme auxotrophs under non-permissive conditions and unable to cause disease in maize seedlings, thus demonstrating the inability of the fungus to acquire sufficient heme from host tissue to support proliferation. Subsequent experiments characterized the role of endocytosis in heme uptake, the susceptibility of the fungus to heme toxicity as well as the transcriptional response to exogenous heme. The latter RNA-seq experiments identified a candidate ABC transporter with a role in the response to heme and xenobiotics. Given the importance of heme biosynthesis for U. maydis pathogenesis, we tested the ability of the well-characterized herbicide BroadStar to influence disease. This herbicide contains the active ingredient flumioxazin, an inhibitor of Hem14 in the heme biosynthesis pathway, and we found that it was an effective antifungal agent for blocking disease in maize. Thus, repurposing herbicides for which resistant plants are available may be an effective strategy to control pathogens and achieve crop protection.

Efficient 7-Dehydrocholesterol Production by Multiple Metabolic Engineering of Diploid Saccharomyces cerevisiae

7-Dehydrocholesterol (7-DHC), a direct precursor of vitamin D3, has attracted increasing attention in microbial fermentation recently. In this study, 7-DHC biosynthesis in diploid Saccharomyces cerevisiae with robust ergosterol production was achieved by heterologous 24-dehydrocholesterol reductase expression, generating 44.1 mg/L 7-DHC, whereas the titer of ergosterol decreased by 40.5%. The ergosterol biosynthetic pathway was completely blocked by knocking out ERG6 and ERG5, affording a 4.2-fold increase in the 7-DHC titer. Subsequently, the facilitation of the mevalonate and the postsqualene pathways accompanied by elimination of transcriptional repressors enhanced 7-DHC synthesis, and the 7-DHC titer reached 738.5 mg/L in a shake flask. Further validation in a 50 L fermenter demonstrated that the 7-DHC titer reached 3.80 g/L within just 24 h, with productivity reaching 158.3 mg/L/h, setting a new benchmark as the highest reported to date. This study paves the way toward a large-scale and cost-effective manufacture of 7-DHC.

Candida glabrata maintains two HAP1 ohnologs, HAP1A and HAP1B, for distinct roles in ergosterol gene regulation to mediate sterol homeostasis under azole and hypoxic conditions

Candida glabrata exhibits innate resistance to azole antifungal drugs but also has the propensity to rapidly develop clinical drug resistance. Azole drugs, which target Erg11, is one of the major classes of antifungals used to treat Candida infections. Despite their widespread use, the mechanism controlling azole-induced ERG gene expression and drug resistance in C. glabrata has primarily revolved around Upc2 and/or Pdr1. Phylogenetic and syntenic analyses revealed that C. glabrata, following a whole genome duplication event, maintained HAP1A and HAP1B, whereas Saccharomyces cerevisiae only retained the HAP1A ortholog, HAP1. In this study, we determined the function of two zinc cluster transcription factors, Hap1A and Hap1B, as direct regulators of ERG genes. In S. cerevisiae, Hap1, an ortholog of Hap1A, is a known transcription factor controlling ERG gene expression under aerobic and hypoxic conditions. Interestingly, deleting HAP1 or HAP1B in either S. cerevisiae or C. glabrata, respectively, showed altered susceptibility to azoles. In contrast, the strain deleted for HAP1A did not exhibit azole susceptibility. We also determined that the increased azole susceptibility in a hap1BΔ strain is attributed to decreased azole-induced expression of ERG genes, resulting in decreased levels of total ergosterol. Surprisingly, Hap1A protein expression is barely detected under aerobic conditions but is specifically induced under hypoxic conditions, where Hap1A is required for the repression of ERG genes. However, in the absence of Hap1A, Hap1B can compensate as a transcriptional repressor. Our study shows that Hap1A and Hap1B is utilized by C. glabrata to adapt to specific host and environmental conditions.

IMPORTANCE

Invasive and drug-resistant fungal infections pose a significant public health concern. Candida glabrata, a human fungal pathogen, is often difficult to treat due to its intrinsic resistance to azole antifungal drugs and its capacity to develop clinical drug resistance. Therefore, understanding the pathways that facilitate fungal growth and environmental adaptation may lead to novel drug targets and/or more efficacious antifungal therapies. While the mechanisms of azole resistance in Candida species have been extensively studied, the roles of zinc cluster transcription factors, such as Hap1A and Hap1B, in C. glabrata have remained largely unexplored until now. Our research shows that these factors play distinct yet crucial roles in regulating ergosterol homeostasis under azole drug treatment and oxygen-limiting growth conditions. These findings offer new insights into how this pathogen adapts to different environmental conditions and enhances our understanding of factors that alter drug susceptibility and/or resistance.

Broad-spectrum antimicrobial activities of a food fermentate of Aspergillus oryzae

Amid persistent concerns over microbial foodborne illnesses and escalating antibiotic resistance, we introduce "NP," a novel and effective broad-spectrum natural antimicrobial product derived from the filtered culture broth of Aspergillus oryzae grown in a food-grade liquid medium. NP demonstrates potent bactericidal activity against a range of food-borne and ESKPAE pathogens, including Staphylococcus aureus (including eight distinct drug-resistant methicillin-resistant Staphylococcus aureus strains), Listeria monocytogenes, Salmonella typhimurium, Klebsiella pneumonia, Pseudomonas aeruginosa, and Escherichia coli (including O157:H7) with minimal inhibitory strength ranging from 25% to 100%. In addition, NP exhibits robust antifungal activity against several human pathogenic fungi including Aspergillus fumigatus, Candida albicans, and the prevalent food spoilage mold Penicillium species, arresting spore germination and vegetative cell growth. Mechanistically, NP disrupts the structural integrity of bacterial and fungal cell membranes, increasing membrane permeability and leading to cell death. Furthermore, genome-wide expression analyses of A. fumigatus vegetative cells exposed to NP reveal the downregulation of genes associated with the liveness of the fungal cells including ergosterol biosynthesis, cell wall maintenance, and development, with network analysis highlighting NP's impact on various metabolic pathways. Notably, NP is presumed safe and thermally stable, holding promise for addressing foodborne illnesses and drug-resistant infections through the development and widespread application of a new generation of antimicrobials.

IMPORTANCE

The development of NP, a potent broad-spectrum antimicrobial, is a significant breakthrough in the ongoing challenge against microbial foodborne illnesses and the growing threat of antibiotic resistance. This food-grade culture broth of Aspergillus oryzae demonstrates exceptional broad-spectrum efficacy against a variety of harmful bacteria and fungi, including drug-resistant strains such as methicillin-resistant Staphylococcus aureus and prevalent food spoilage molds. NP exhibits strong bactericidal activity against various foodborne and ESKAPE pathogens, and strong antifungal activity against Penicillium species, Aspergillus fumigatus, and Candida albicans. The potent bactericidal and antifungal properties of NP are a result of its ability to disrupt microbial cell membranes leading to increased permeability. Furthermore, the genome-wide impact of NP on fungal gene expression and metabolic pathways underscores its comprehensive antimicrobial action, leading to transcriptomic and metabolic changes associated with cell death in A. fumigatus.

Insights into the role of sterol metabolism in antifungal drug resistance: a mini-review

Sterols are essential for eukaryotic cells and are crucial in cellular membranes' structure, function, fluidity, permeability, adaptability to environmental stressors, and host-pathogen interactions. Fungal sterol, such as ergosterol metabolism, involves several organelles, including the mitochondria, lipid droplets, endoplasmic reticulum, and peroxisomes that can be regulated mainly by feedback mechanisms and transcriptionally. The majority of sterol transport in yeast occurs via non-vesicular transport pathways mediated by lipid transfer proteins, which determine the quantity of sterol present in the cell membrane. Pathogenic fungi Candida, Aspergillus, and Cryptococcus species can cause a range of superficial to potentially fatal systemic and invasive infections that are more common in immunocompromised patients. There is a significant risk of morbidity and mortality from these infections, which are very difficult to cure. Several antifungal drugs with different modes of action have received clinical approval to treat fungal infections. Antifungal drugs targeting the ergosterol biosynthesis pathway are well-known for their antifungal activity; however, an imbalance in the regulation and transport of ergosterol could lead to resistance to antifungal therapy. This study summarizes how fungal sterol metabolism and regulation can modulate sterol-targeting antifungal drug resistance.

Role of Squalene Epoxidase Gene (SQE1) in the Response of the Lichen Lobaria pulmonaria to Temperature Stress

Currently, due to the increasing impact of anthropogenic factors and changes in solar activity, the temperature on Earth is rising, posing a threat to biodiversity. Lichens are among the most sensitive organisms to climate change. Elevated ambient temperatures can have a significant impact on lichens, resulting in more frequent and intense drying events that can impede metabolic activity. It has been suggested that the possession of a diverse sterol composition may contribute to the tolerance of lichens to adverse temperatures and other biotic and abiotic stresses. The major sterol found in lichens is ergosterol (ERG); however, the regulation of the ERG biosynthetic pathway, specifically the step of epoxidation of squalene to 2,3-oxidosqualene catalyzed by squalene epoxidase during stress, has not been extensively studied. In this study, we used lichen Lobaria pulmonaria as a model species that is well known to be sensitive to air pollution and habitat loss. Using in silico analysis, we identified cDNAs encoding squalene epoxidase from L. pulmonaria, designating them as LpSQE1 for the mycobiont and SrSQE1 for the photobiont Symbiochloris reticulata. Our results showed that compared with a control kept at room temperature (+20 °C), mild temperatures (+4 °C and +30 °C) did not affect the physiology of L. pulmonaria, assessed by changes in membrane integrity, respiration rates, and PSII activity. An extreme negative temperature (-20 °C) noticeably inhibited respiration but did not affect membrane stability. In contrast, treating lichen with a high positive temperature (+40 °C) significantly reduced all physiological parameters. Quantitative PCR analysis revealed that exposing thalli to -20 °C, +4 °C, +30 °C, and +40 °C stimulated the expression levels of LpSQE1 and SrSQE1 and led to a significant upregulation of Hsps. These data provide new information regarding the roles of sterols and Hsps in the response of lichens to climate change.

Review of the Structural Characteristics and Biological Activities of Tricholoma Secondary Metabolites (2018-2023)

Tricholoma are significant medicinal and edible mushrooms within Basidiomycota. Known for their various medicinal properties such as anti-tumor, immune regulation, and antioxidant effects, they are regarded worldwide as health foods of the 21st century. Tricholoma species produce various types of secondary metabolites, which have been extensively studied by the scientific community. In 2018, Clericuzio et al. summarized the structures, biosynthesis, and biological activities of over one hundred different secondary metabolites isolated from the fruiting bodies of 25 Tricholoma species. Building on this, the present article reviews the research progress on Tricholoma secondary metabolites from 2018 to 2023, identifying a total of 101 compounds, 46 of which were newly discovered. These secondary metabolites include a wide range of chemical categories such as terpenoids, steroids, and alkaloids, demonstrating broad biological activities. This article aims to provide in-depth scientific insights and guidance for researchers in this field by summarizing the chemical and biological properties of these secondary metabolites, promoting further applications and development of Tricholoma fungi in the pharmaceutical and food industries.

Hyperproduction of 7-dehydrocholesterol by rewiring the post-squalene module in lipid droplets of Saccharomyces cerevisiae

Lipid droplets (LDs) are specialized organelles that store neutral lipids to reduce the negative effects of lipotoxicity on cells. However, many neutral lipids are precursors for the synthesis of sterols and complex terpenoids, and this sequestration often greatly limits the efficient biosynthesis of sterols and complex terpenoids. In this study, taking 7-dehydrocholesterol (7-DHC) synthesis in Saccharomyces cerevisiae as an example, we revealed the blocking mechanism of LD sequestration on the efficient synthesis of metabolic products and found that LDs can sequester a significant amount of squalene, the precursor of 7-DHC, effectively preventing it from being directed toward the post-squalene pathway. Based on this, a post-squalene pathway was reconstructed on LDs, which resulted in a 28.7% increase in the 7-DHC titer, reaching 684.1 mg/L, whereas the squalene titer was reduced by approximately 97%. Subsequently, the triacylglycerol degradation pathway was weakened to release the storage space in LDs, and the esterification pathway was concurrently strengthened to guide 7-DHC storage within LDs, which further increased 7-DHC production, reaching 792.9 mg/L. Finally, by reducing the NADH/NAD + ratio to alleviate the redox imbalance, the 7-DHC titer reached 867.6 mg/L in shake flask and 5.1 g/L in a 3-L bioreactor, which is the highest reported titer to date. In summary, this study provides new insights into the important role of LDs in sterol synthesis and offers a novel strategy for constructing cell factories for the efficient synthesis of sterol compounds.

Perturbations in mitochondrial metabolism associated with defective cardiolipin biosynthesis: An in-organello real-time NMR study

Mitochondria are central to cellular metabolism; hence, their dysfunction contributes to a wide array of human diseases. Cardiolipin, the signature phospholipid of the mitochondrion, affects proper cristae morphology, bioenergetic functions, and metabolic reactions carried out in mitochondrial membranes. To match tissue-specific metabolic demands, cardiolipin typically undergoes an acyl tail remodeling process with the final step carried out by the phospholipid-lysophospholipid transacylase tafazzin. Mutations in tafazzin are the primary cause of Barth syndrome. Here, we investigated how defects in cardiolipin biosynthesis and remodeling impacts metabolic flux through the TCA cycle and associated yeast pathways. Nuclear magnetic resonance was used to monitor in real-time the metabolic fate of 13C3-pyruvate in isolated mitochondria from three isogenic yeast strains. We compared mitochondria from a WT strain to mitochondria from a Δtaz1 strain that lacks tafazzin and contains lower amounts of unremodeled cardiolipin and mitochondria from a Δcrd1 strain that lacks cardiolipin synthase and cannot synthesize cardiolipin. We found that the 13C-label from the pyruvate substrate was distributed through twelve metabolites. Several of the metabolites were specific to yeast pathways including branched chain amino acids and fusel alcohol synthesis. While most metabolites showed similar kinetics among the different strains, mevalonate concentrations were significantly increased in Δtaz1 mitochondria. Additionally, the kinetic profiles of α-ketoglutarate, as well as NAD+ and NADH measured in separate experiments, displayed significantly lower concentrations for Δtaz1 and Δcrd1 mitochondria at most time points. Taken together, the results show how cardiolipin remodeling influences pyruvate metabolism, tricarboxylic acid cycle flux, and the levels of mitochondrial nucleotides.

Deciphering the antiochratoxigenic activity of plant extracts and Debaryomyces hansenii against Penicillium nordicum in a "chorizo"-based medium by proteomic analysis

Penicillium nordicum is the main ochratoxin A (OTA)-producing species on the surface of dry-fermented sausages, such as the "chorizo". New antifungal strategies are being developed using biocontrol agents (BCAs), such as plant extracts and native microorganisms. This work aimed to evaluate the antiochratoxigenic capacity and the causative modes of action of BCAs (rosemary essential oil (REO), acorn shell extract and the yeast Debaryomyces hansenii (Dh)) in a "chorizo"-based medium (Ch-DS). BCAs were inoculated on Ch-DS together with P. nordicum and incubated at 12 °C for 15 days to collect mycelia for OTA analyses and comparative proteomics. Both REO and Dh alone decreased OTA accumulation up to 99% and affected the abundance of P. nordicum proteins linked to cell wall organisation, synthesis of OTA-related metabolites and ergosterol synthesis. It is worth highlighting the increased abundance of an amidase by REO, matching with the decrease in OTA. The use of REO and Dh as BCAs could be an effective strategy to reduce the OTA hazard in the meat industry. Based on their not fully coincident modes of action, their combined application could be of interest in "chorizo" to maximise their potential against ochratoxigenic strains.

Parallel evolution of fluconazole resistance and tolerance in Candida glabrata

Introduction

With the growing population of immunocompromised individuals, opportunistic fungal pathogens pose a global health threat. Candida species, particularly C. albicans and non-albicans Candida species such as C. glabrata, are the most prevalent pathogenic fungi. Azoles, especially fluconazole, are widely used therapeutic options.

Objective

This study investigates how C. glabrata adapts to fluconazole, with a focus on understanding the factors regulating fluconazole tolerance and its relationship to resistance.

Methods

This study compared the factors regulating fluconazole tolerance between C. albicans and C. glabrata. We analyzed the impact of temperature on fluconazole tolerance, and requirement of calcineurin and Hsp90 for maintenance of fluconazole tolerance. We isolated colonies from edge, inside and outside of inhibition zone in disk diffusion assays. And we exposed C. glabrata strain to high concentrations of fluconazole and investigated the mutants for development of fluconazole resistance and tolerance.

Results

We found temperature modulated tolerance in the opposite way in C. albicans strain YJB-T1891 and C. glabrata strain CG4. Calcineurin and Hsp90 were required for maintenance of fluconazole tolerance in both species. Colonies from inside and outside of inhibition zones did not exhibited mutated phenotype, but colonies isolated from edge of inhibition zone exhibited diverse phenotype changes. Moreover, we discovered that high concentrations (16-128 μg/mL) of fluconazole induce the simultaneous but parallel development of tolerance and resistance in C. glabrata, unlike the sole development of tolerance in C. albicans.

Conclusion

This study highlights that while tolerance to fluconazole is a common response in Candida species, the specific molecular mechanisms and evolutionary pathways that lead to this response vary between species. Our findings emphasize the importance of understanding the regulation of fluconazole tolerance in different Candida species to develop effective therapeutic strategies.

Changes in Ergosterol Biosynthesis Alter the Response to Cycloheximide, 4-Nitroquinoline-N-Oxide, Weak Organic Acids, and Virulence in Candida glabrata

The ERG6 gene encodes the sterol C24-methyltransferase converting zymosterol to fecosterol in the ergosterol biosynthetic pathway. Here, we extend the results of functional analysis of the CgERG6 gene, which was previously shown to modulate drug susceptibility in Candida glabrata mutant cells, by demonstrating that its deletion leads to increased susceptibility to cycloheximide, 4-nitroquinoline-N-oxide and weak organic acids, and such effects are associated with attenuated virulence. Together with abrogated efflux of drug substrates by CgCdr1p and CgPdr12p, the Cgerg6Δ mutation leads to reduced cell surface hydrophobicity and decreased virulence of the mutant cells of C. glabrata. The absence of CgErg6p impacts the lipid organization and function of the plasma membrane, resulting in non-specific permeability and abrogation of normal function of membrane-bound proteins accompanied by decreased virulence in Cgerg6Δ cells. Galleria mellonella larvae were used as a non-vertebrate animal host model to determine differences in the virulence potential of C. glabrata strains (parental strain and the Cgerg6Δ deletion mutant). We found that Cgerg6Δ mutant strain attenuated in virulence caused 25-30% survival of larvae compared with parental strain.

From β-Carotene to Retinoids: A Review of Microbial Production of Vitamin A

Vitamin A (retinoids) is crucial for human health, with significant demand across the food, pharmaceutical, and animal feed industries. Currently, the market primarily relies on chemical synthesis and natural extraction methods, which face challenges such as low synthesis efficiency and complex extraction processes. Advances in synthetic biology have enabled vitamin A biosynthesis using microbial cell factories, offering a promising and sustainable solution to meet the increasing market demands. This review introduces the key enzymes involved in the biosynthesis of vitamin A from β-carotene, evaluates achievements in vitamin A production using various microbial hosts, and summarizes strategies for optimizing vitamin A biosynthesis. Additionally, we outline the remaining challenges and propose future directions for the biotechnological production of vitamin A.

In vitro and in vivo synergistic inhibition of Malassezia furfur targeting cell membranes by Rosa rugosa Thunb. and Coptidis Rhizoma extracts

Background

Malassezia furfur (M. furfur) is a prevalent dermatophyte that significantly impairs patients' quality of life. This study aimed to evaluate the synergistic antifungal effects of combined extracts from Rosa rugosa Thunb. (MG) and Coptidis Rhizoma (HL) against M. furfur, both in vitro and in vivo.

Methods

High-performance liquid chromatography (HPLC) was used to identify the major active compounds present in MG and HL. The antifungal activity of the combined Meilian extract (ML) was assessed using the checkerboard method and time-kill curves. Microstructural alterations in the fungi were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The impact of the extracts on the fungal cell membrane was investigated through propidium iodide staining, protein concentration assays, and ergosterol quantification. Transcriptomic analysis was conducted to elucidate the molecular mechanisms underlying the effects of the extracts. Furthermore, the synergistic antifungal effects of ML were evaluated in a mouse model of seborrheic dermatitis induced by M. furfur.

Results

The study demonstrated that the combined application of MG and HL significantly affected the integrity of the M. furfur cell membrane and potentially modulated its formation processes. In the M. furfur-induced seborrheic dermatitis model, ML exhibited synergistic antifungal effects and effectively alleviated skin inflammation. These findings provide an important theoretical basis for understanding the antifungal mechanisms of ML and its potential application in dermatological therapy.

The Recent Progress of Tricyclic Aromadendrene-Type Sesquiterpenoids: Biological Activities and Biosynthesis

The tricyclic-aromadendrene-type sesquiterpenes are widely distributed and exhibit a range of biological activities, including anti-inflammatory, analgesic, antioxidant, antibacterial, insecticidal and cytotoxic properties. Several key sesquiterpene synthases (STSs) of this type have been identified, of which, viridiflorol synthase has been engineered for efficiently biosynthesizing viridiflorol in an Escherichia coli strain. This paper comprehensively summarizes the distribution and biological activity of aromadendrene-type sesquiterpenes in plant essential oils and microorganisms. The progress in aromadendrene-type sesquiterpene biosynthesis research, including the modifications of key STSs and the optimization of synthetic pathways, is reviewed. Finally, the prospects and associated challenges for the application and biosynthesis of these natural products are also discussed.

Otilonium Bromide Exhibits Potent Antifungal Effects by Blocking Ergosterol Plasma Membrane Localization and Triggering Cytotoxic Autophagy in Candida Albicans

Candidiasis, which presents a substantial risk to human well-being, is frequently treated with azoles. However, drug-drug interactions caused by azoles inhibiting the human CYP3A4 enzyme, together with increasing resistance of Candida species to azoles, represent serious issues with this class of drug, making it imperative to develop innovative antifungal drugs to tackle this growing clinical challenge. A drug repurposing approach is used to examine a library of Food and Drug Administration (FDA)-approved drugs, ultimately identifying otilonium bromide (OTB) as an exceptionally encouraging antifungal agent. Mechanistically, OTB impairs vesicle-mediated trafficking by targeting Sec31, thereby impeding the plasma membrane (PM) localization of the ergosterol transporters, such as Sip3. Consequently, OTB obstructs the movement of ergosterol across membranes and triggers cytotoxic autophagy. It is noteworthy that C. albicans encounters challenges in developing resistance to OTB because it is not a substrate for drug transporters. This study opens a new door for antifungal therapy, wherein OTB disrupts ergosterol subcellular distribution and induces cytotoxic autophagy. Additionally, it circumvents the hepatotoxicity associated with azole-mediated liver enzyme inhibition and avoids export-mediated drug resistance in C. albicans.

Verazine biosynthesis from simple sugars in engineered Saccharomyces cerevisiae

Steroidal alkaloids are FDA-approved drugs (e.g., Zytiga) and promising drug candidates/leads (e.g., cyclopamine); yet many of the ≥697 known steroidal alkaloid natural products remain underutilized as drugs because it can be challenging to scale their biosynthesis in their producing organisms. Cyclopamine is a steroidal alkaloid produced by corn lily (Veratrum spp.) plants, and it is an inhibitor of the Hedgehog (Hh) signaling pathway. Therefore, cyclopamine is an important drug candidate/lead to treat human diseases that are associated with dysregulated Hh signaling, such as basal cell carcinoma and acute myeloid leukemia. Cyclopamine and its semi-synthetic derivatives have been studied in (pre)clinical trials as Hh inhibitor-based drugs. However, challenges in scaling the production of cyclopamine have slowed efforts to improve its efficacy and safety profile through (bio)synthetic derivatization, often limiting drug development to synthetic analogs of cyclopamine such as the FDA-approved drugs Odomzo, Daurismo, and Erivedge. If a platform for the scalable and sustainable production of cyclopamine were established, then its (bio)synthetic derivatization, clinical development, and, ultimately, widespread distribution could be accelerated. Ongoing efforts to achieve this goal include the biosynthesis of cyclopamine in Veratrum plant cell culture and the semi-/total chemical synthesis of cyclopamine. Herein, this work advances efforts towards a promising future approach: the biosynthesis of cyclopamine in engineered microorganisms. We completed the heterologous microbial production of verazine (biosynthetic precursor to cyclopamine) from simple sugars (i.e., glucose and galactose) in engineered Saccharomyces cerevisiae (S. cerevisiae) through the inducible upregulation of the native yeast mevalonate and lanosterol biosynthetic pathways, diversion of biosynthetic flux from ergosterol (i.e., native sterol in S. cerevisiae) to cholesterol (i.e., biosynthetic precursor to verazine), and expression of a refactored five-step verazine biosynthetic pathway. The engineered S. cerevisiae strain that produced verazine contains eight heterologous enzymes sourced from seven different species. Importantly, S. cerevisiae-produced verazine was indistinguishable via liquid chromatography-mass spectrometry from both a commercial standard (Veratrum spp. plant-produced) and Nicotiana benthamiana-produced verazine. To the best of our knowledge, this is the first report describing the heterologous production of a steroidal alkaloid in an engineered yeast. Verazine production was ultimately increased through design-build-test-learn cycles to a final titer of 83 ± 3 μg/L (4.1 ± 0.1 μg/g DCW). Together, this research lays the groundwork for future microbial biosynthesis of cyclopamine, (bio)synthetic derivatives of cyclopamine, and other steroidal alkaloid natural products.

tRNA-m1A methylation controls the infection of Magnaporthe oryzae by supporting ergosterol biosynthesis

Ergosterols are essential components of fungal plasma membranes. Inhibitors targeting ergosterol biosynthesis (ERG) genes are critical for controlling fungal pathogens, including Magnaporthe oryzae, the fungus that causes rice blast. However, the translational mechanisms governing ERG gene expression remain largely unexplored. Here, we show that the Trm6/Trm61 complex catalyzes dynamic N1-methyladenosine at position 58 (m1A58) in 51 transfer RNAs (tRNAs) of M. oryzae, significantly influencing translation at both the initiation and elongation stages. Notably, tRNA m1A58 promotes elongation speed at most cognate codons mainly by enhancing eEF1-tRNA binding rather than affecting tRNA abundance or charging. The absence of m1A58 leads to substantial decreases in the translation of ERG genes, ergosterol production, and, consequently, fungal virulence. Simultaneously targeting the Trm6/Trm61 complex and the ergosterol biosynthesis pathway markedly improves rice blast control. Our findings demonstrate an important role of m1A58-mediated translational regulation in ergosterol production and fungal infection, offering a potential strategy for fungicide development.

Rational selection of morphological phenotypic traits to extract essential similarities in chemical perturbation in the ergosterol pathway

Terbinafine, fluconazole, and amorolfine inhibit fungal ergosterol synthesis by acting on their target enzymes at different steps in the synthetic pathway, causing the accumulation of various intermediates. We found that the effects of these three in- hibitors on yeast morphology were different. The number of morphological parameters commonly altered by these drugs was only approximately 6% of the total. Using a rational strategy to find commonly changed parameters,we focused on hidden essential similarities in the phenotypes possibly due to decreased ergosterol levels. This resulted in higher apparent morphological similarity. Improvements in morphological similarity were observed even when canonical correlation analysis was used to select biologically meaningful morphological parameters related to gene function. In addition to changes in cell morphology, we also observed differences in the synergistic effects among the three inhibitors and in their fungicidal effects against pathogenic fungi possibly due to the accumulation of different intermediates. This study provided a comprehensive understanding of the properties of inhibitors acting in the same biosynthetic pathway.

D-Limonene Inhibits Pichia kluyveri Y-11519 in Sichuan Pickles by Disrupting Metabolism

The Pichia kluyveri, a proliferation commonly found in Sichuan pickles (SCPs), can accelerate the growth and reproduction of spoilage bacteria, causing off-odor development and decay. Although D-limonene, a common natural preservative, effectively restricts P. kluyveri, its inhibitory mechanism remains unclear. This study aimed to elucidate this molecular mechanism by investigating the impact on basic P. kluyveri metabolism. The findings revealed that D-limonene inhibited P. kluyveri growth and disrupted the transcription of the genes responsible for encoding the enzymes involved in cell wall and membrane synthesis, oxidative phosphorylation, glycolysis, and the tricarboxylic acid (TCA) cycle pathway. The results indicated that these events disrupted crucial metabolism such as cell wall and membrane integrity, adenosine triphosphate (ATP) synthesis, and reactive oxygen species (ROS) balance. These insights provided a comprehensive understanding of the inhibitory effect of D-limonene on the growth and reproduction of P. kluyveri while highlighting its potential application in the SCP industry.

Inhibitory Effects and Mechanisms of Perilla Essential Oil and Perillaldehyde against Chestnut Pathogen Botryosphaeria dothidea

Botryosphaeria dothidea, a notorious plant pathogen, is responsible for causing chestnut rot during postharvest storage. This research aimed to assess the antifungal properties of perilla essential oil (PEO) and perillaldehyde (PAE) against B. dothidea. PEO's and PAE's inhibitory effects on B. dothidea were investigated using an agar dilution method, a fumigation method, and an in vivo assay in chestnuts and shell buckets. Based on the results of gas chromatography-mass spectrometry, it was confirmed that the main component of PEO was elemicin. The antifungal mechanism of PEO and PAE against B. dothidea was investigated by conducting staining experiments of the fungal cell wall and cell membrane. PEO and PAE strongly inhibit the mycelial growth of B. dothidea in a dose-dependent manner. The inhibitory mechanism is mainly related to the destruction of the integrity of the fungal cell wall and plasma membrane. Notably, PEO retains its antifungal efficacy against B. dothidea in chestnuts, effectively prolonging their storage life. These findings indicate that PEO and PAE are nontoxic, eco-friendly botanical fungicides, holding promise for controlling postharvest chestnut rot.

The Anti-Inflammatory Effects and Mechanism of the Submerged Culture of Ophiocordyceps sinensis and Its Possible Active Compounds

The pharmacological effects of the fruiting body of Ophiocordyceps sinensis (O. sinensis) such as antioxidant, anti-virus, and immunomodulatory activities have already been described, whereas the anti-inflammatory effects and active components of the submerged culture of O. sinesis (SCOS) still need to be further verified. This study aimed to investigate the active compounds in the fermented liquid (FLOS), hot water (WEOS), and 50-95% (EEOS-50, EEOS-95) ethanol extracts of SCOS and their anti-inflammatory effects and potential mechanisms in lipopolysaccharide (LPS)-stimulated microglial BV2 cells. The results demonstrated that all of the SCOS extracts could inhibit NO production in BV2 cells. EEOS-95 exhibited the strongest inhibitory effects (71% inhibitory ability at 500 µg/mL), and its ergosterol, γ-aminobutyric acid (GABA), total phenolic, and total flavonoid contents were significantly higher than those of the other extracts (18.60, 18.60, 2.28, and 2.14 mg/g, p < 0.05, respectively). EEOS-95 also has a strong inhibitory ability against IL-6, IL-1β, and TNF-α with an IC50 of 617, 277, and 507 µg/mL, respectively, which is higher than that of 1 mM melatonin. The anti-inflammatory mechanism of EEOS-95 seems to be associated with the up-regulation of PPAR-γ/Nrf-2/HO-1 antioxidant-related expression and the down-regulation of NF-κB/COX-2/iNOS pro-inflammatory expression signaling. In summary, we demonstrated that EEOS-95 exhibits neuroinflammation-mediated neurodegenerative disorder activities in LPS-induced inflammation in brain microglial cells.

Decoding the Role of CYP450 Enzymes in Metabolism and Disease: A Comprehensive Review

Cytochrome P450 (CYP450) is a group of enzymes that play an essential role in Phase I metabolism, with 57 functional genes classified into 18 families in the human genome, of which the CYP1, CYP2, and CYP3 families are prominent. Beyond drug metabolism, CYP enzymes metabolize endogenous compounds such as lipids, proteins, and hormones to maintain physiological homeostasis. Thus, dysregulation of CYP450 enzymes can lead to different endocrine disorders. Moreover, CYP450 enzymes significantly contribute to fatty acid metabolism, cholesterol synthesis, and bile acid biosynthesis, impacting cellular physiology and disease pathogenesis. Their diverse functions emphasize their therapeutic potential in managing hypercholesterolemia and neurodegenerative diseases. Additionally, CYP450 enzymes are implicated in the onset and development of illnesses such as cancer, influencing chemotherapy outcomes. Assessment of CYP450 enzyme expression and activity aids in evaluating liver health state and differentiating between liver diseases, guiding therapeutic decisions, and optimizing drug efficacy. Understanding the roles of CYP450 enzymes and the clinical effect of their genetic polymorphisms is crucial for developing personalized therapeutic strategies and enhancing drug responses in diverse patient populations.

Engineering sub-organelles of a diploid Saccharomyces cerevisiae to enhance the production of 7-dehydrocholesterol

7-Dehydrocholesterol (7-DHC) is widely present in various organisms and is an important precursor of vitamin D3. Despite significant improvements in the biosynthesis of 7-DHC, it remains insufficient to meet the industrial demands. In this study, we reported high-level production of 7-DHC in an industrial Saccharomyces cerevisiae leveraging subcellular organelles. Initially, the copy numbers of DHCR24 were increased in combination with sterol transcriptional factor engineering and rebalanced the redox power of the strain. Subsequently, the effects of compartmentalizing the post-squalene pathway in peroxisomes were validated by assembling various pathway modules in this organelle. Furthermore, several peroxisomes engineering was conducted to enhance the production of 7-DHC. Utilizing the peroxisome as a vessel for partial post-squalene pathways, the potential of yeast for 7-dehydrocholesterol production was demonstrated by achieving a 26-fold increase over the initial production level. 7-DHC titer reached 640.77 mg/L in shake flasks and 4.28 g/L in a 10 L bench-top fermentor, the highest titer ever reported. The present work lays solid foundation for large-scale and cost-effective production of 7-DHC for practical applications.

The response mechanism analysis of HMX1 knockout strain to levulinic acid in Saccharomyces cerevisiae

Levulinic acid, a hydrolysis product of lignocellulose, can be metabolized into important compounds in the field of medicine and pesticides by engineered strains of Saccharomyces cerevisiae. Levulinic acid, as an intermediate product widely found in the conversion process of lignocellulosic biomass, has multiple applications. However, its toxicity to Saccharomyces cerevisiae reduces its conversion efficiency, so screening Saccharomyces cerevisiae genes that can tolerate levulinic acid becomes the key. By creating a whole-genome knockout library and bioinformatics analysis, this study used the phenotypic characteristics of cells as the basis for screening and found the HMX1 gene that is highly sensitive to levulinic acid in the oxidative stress pathway. After knocking out HMX1 and treating with levulinic acid, the omics data of the strain revealed that multiple affected pathways, especially the expression of 14 genes related to the cell wall and membrane system, were significantly downregulated. The levels of acetyl-CoA and riboflavin decreased by 1.02-fold and 1.44-fold, respectively, while the content of pantothenic acid increased. These findings indicate that the cell wall-membrane system, as well as the metabolism of acetyl-CoA and riboflavin, are important in improving the resistance of Saccharomyces cerevisiae to levulinic acid. They provide theoretical support for enhancing the tolerance of microorganisms to levulinic acid, which is significant for optimizing the conversion process of lignocellulosic biomass to levulinic acid.

Candida glabrata maintains two Hap1 homologs, Zcf27 and Zcf4, for distinct roles in ergosterol gene regulation to mediate sterol homeostasis under azole and hypoxic conditions

Candida glabrata exhibits innate resistance to azole antifungal drugs but also has the propensity to rapidly develop clinical drug resistance. Azole drugs, which target Erg11, is one of the three major classes of antifungals used to treat Candida infections. Despite their widespread use, the mechanism controlling azole-induced ERG gene expression and drug resistance in C. glabrata has primarily revolved around Upc2 and/or Pdr1. In this study, we determined the function of two zinc cluster transcription factors, Zcf27 and Zcf4, as direct but distinct regulators of ERG genes. Our phylogenetic analysis revealed C. glabrata Zcf27 and Zcf4 as the closest homologs to Saccharomyces cerevisiae Hap1. Hap1 is a known zinc cluster transcription factor in S. cerevisiae in controlling ERG gene expression under aerobic and hypoxic conditions. Interestingly, when we deleted HAP1 or ZCF27 in either S. cerevisiae or C. glabrata, respectively, both deletion strains showed altered susceptibility to azole drugs, whereas the strain deleted for ZCF4 did not exhibit azole susceptibility. We also determined that the increased azole susceptibility in a zcf27Δ strain is attributed to decreased azole-induced expression of ERG genes, resulting in decreased levels of total ergosterol. Surprisingly, Zcf4 protein expression is barely detected under aerobic conditions but is specifically induced under hypoxic conditions. However, under hypoxic conditions, Zcf4 but not Zcf27 was directly required for the repression of ERG genes. This study provides the first demonstration that Zcf27 and Zcf4 have evolved to serve distinct roles allowing C. glabrata to adapt to specific host and environmental conditions.

Perturbations in mitochondrial metabolism associated with defective cardiolipin biosynthesis: An in-organello real-time NMR study

Mitochondria are central to cellular metabolism; hence, their dysfunction contributes to a wide array of human diseases including cancer, cardiopathy, neurodegeneration, and heritable pathologies such as Barth syndrome. Cardiolipin, the signature phospholipid of the mitochondrion promotes proper cristae morphology, bioenergetic functions, and directly affects metabolic reactions carried out in mitochondrial membranes. To match tissue-specific metabolic demands, cardiolipin typically undergoes an acyl tail remodeling process with the final step carried out by the phospholipid-lysophospholipid transacylase tafazzin. Mutations in the tafazzin gene are the primary cause of Barth syndrome. Here, we investigated how defects in cardiolipin biosynthesis and remodeling impact metabolic flux through the tricarboxylic acid cycle and associated pathways in yeast. Nuclear magnetic resonance was used to monitor in real-time the metabolic fate of 13C3-pyruvate in isolated mitochondria from three isogenic yeast strains. We compared mitochondria from a wild-type strain to mitochondria from a Δtaz1 strain that lacks tafazzin and contains lower amounts of unremodeled cardiolipin, and mitochondria from a Δcrd1 strain that lacks cardiolipin synthase and cannot synthesize cardiolipin. We found that the 13C-label from the pyruvate substrate was distributed through about twelve metabolites. Several of the identified metabolites were specific to yeast pathways, including branched chain amino acids and fusel alcohol synthesis. Most metabolites showed similar kinetics amongst the different strains but mevalonate and α-ketoglutarate, as well as the NAD+/NADH couple measured in separate nuclear magnetic resonance experiments, showed pronounced differences. Taken together, the results show that cardiolipin remodeling influences pyruvate metabolism, tricarboxylic acid cycle flux, and the levels of mitochondrial nucleotides.

Updates on antifungal pharmacotherapy in elasmobranchs: pharmacokinetics of 4 mg/kg voriconazole after IM and IV administration in undulate skates (Raja undulata) maintained under human care

Introduction

Fungal diseases are frequently associated with elevated mortality rates in elasmobranchs. Currently, there is a notable absence of scientifically validated therapeutic medications that can ensure both effectiveness and safety when administered to this group of animals. The empirical prescription of azole antifungal agents, particularly voriconazole, has been posited as a potentially efficacious treatment approach for addressing most common mycoses in sharks and rays. However, there are still no published pharmacokinetic studies supporting its use in elasmobranchs and there is a lack of scientific base for its utilization in elasmobranchs.

Methods

For this study, voriconazole was administered intravenously (IV) and intramuscularly (IM), at a single dose of 4 mg/kg to six adult undulate skates (Raja undulata). A washout period of 8 weeks was left between each route of administration. Blood samples were collected both before and at ten predetermined intervals after each dosing (0.25, 0.5, 1, 1.5, 2, 4, 8, 12, 24, and 36 h after drug administration). Plasma concentrations were quantified using a validated high-performance liquid chromatography method, and pharmacokinetic (PK) data was analyzed through non-compartmental methods.

Results

The mean extrapolated concentration at 0 h (C0) after IV administration was 27.19 ± 7.15 μg/mL and the mean peak plasma concentrations (Cmax) ± SEM after IM administration resulted 2.98 ± 0.28 μg/mL at a mean time to maximum concentration (T max) of 1.33 ± 0.17 h. Terminal half-lives were calculated and resulted 11.18 ± 1.32 h for IV injections and 9.59 ± 1.38 h for IM injections. The area under the curve extrapolated to infinity was determined as 58.14 ± 2.79 h·μg/ml following IV injections and 37.60 ± 6.67 h·μg/ml following IM injections. The IM-administered voriconazole exhibited a mean absolute bioavailability of 64.67 ± 11.47%.

Discussion

These discoveries provide backing for the possible application of voriconazole through the intramuscular route in undulate skates and support using lower dosage regimens compared to those required for oral administration, emphasizing the importance of conducting further pharmacokinetic studies with antifungals in elasmobranchs.

The sterol C-24 methyltransferase encoding gene, erg6, is essential for viability of Aspergillus species

Triazoles, the most widely used class of antifungal drugs, inhibit the biosynthesis of ergosterol, a crucial component of the fungal plasma membrane. Inhibition of a separate ergosterol biosynthetic step, catalyzed by the sterol C-24 methyltransferase Erg6, reduces the virulence of pathogenic yeasts, but its effects on filamentous fungal pathogens like Aspergillus fumigatus remain unexplored. Here, we show that the lipid droplet-associated enzyme Erg6 is essential for the viability of A. fumigatus and other Aspergillus species, including A. lentulus, A. terreus, and A. nidulans. Downregulation of erg6 causes loss of sterol-rich membrane domains required for apical extension of hyphae, as well as altered sterol profiles consistent with the Erg6 enzyme functioning upstream of the triazole drug target, Cyp51A/Cyp51B. Unexpectedly, erg6-repressed strains display wild-type susceptibility against the ergosterol-active triazole and polyene antifungals. Finally, we show that erg6 repression results in significant reduction in mortality in a murine model of invasive aspergillosis. Taken together with recent studies, our work supports Erg6 as a potentially pan-fungal drug target.

Antifungal Potential of Secondary Metabolites Derived from Arcangelisia flava (L.) Merr.: An Analysis of In Silico Enzymatic Inhibition and In Vitro Efficacy against Candida Species

Considering the escalating resistance to conventional antifungal medications, it is critical to identify novel compounds that can efficiently counteract this challenge. The purpose of this research was to elucidate the fungicidal properties of secondary metabolites derived from Arcangelisia flava, with a specific focus on their efficacy against Candida species. This study utilized a combination approach comprising laboratory simulations and experiments to discern and evaluate the biologically active constituents present in the dichloromethane extract of A. flava. The in vitro experiments demonstrated that compounds 1 (palmatine) and 2 (fibraurin) exhibited antifungal properties. The compounds exhibited minimum inhibitory concentrations (MICs) ranging from 15.62 to 62.5 µg/mL against Candida sp. Moreover, compound 1 demonstrated a minimum fungicidal concentration (MFC) of 62.5 µg/mL against Candida glabrata and C. krusei. In contrast, compound 2 exhibited an MFC of 125 µg/mL against both Candida species. Based on a molecular docking study, it was shown that compounds 1 and 2 have a binding free energy of -6.6377 and -6.7075 kcal/mol, respectively, which indicates a strong affinity and specificity for fungal enzymatic targets. This study utilized pharmacophore modeling and Density Functional Theory (DFT) simulations to better understand the interaction dynamics and structural properties crucial for antifungal activity. The findings underscore the potential of secondary metabolites derived from A. flava to act as a foundation for creating novel and highly efficient antifungal treatments, specifically targeting fungal diseases resistant to existing treatment methods. Thus, the results regarding these compounds can provide references for the next stage in antifungal drug design. Further investigation is necessary to thoroughly evaluate these natural substances' clinical feasibility and safety characteristics, which show great potential as antifungal agents.

The molecular mechanism of on-demand sterol biosynthesis at organelle contact sites

Contact-sites are specialized zones of proximity between two organelles, essential for organelle communication and coordination. The formation of contacts between the Endoplasmic Reticulum (ER), and other organelles, relies on a unique membrane environment enriched in sterols. However, how these sterol-rich domains are formed and maintained had not been understood. We found that the yeast membrane protein Yet3, the homolog of human BAP31, is localized to multiple ER contact sites. We show that Yet3 interacts with all the enzymes of the post-squalene ergosterol biosynthesis pathway and recruits them to create sterol-rich domains. Increasing sterol levels at ER contacts causes its depletion from the plasma membrane leading to a compensatory reaction and altered cell metabolism. Our data shows that Yet3 provides on-demand sterols at contacts thus shaping organellar structure and function. A molecular understanding of this protein's functions gives new insights into the role of BAP31 in development and pathology.

Analysis of clinical Candida parapsilosis isolates reveals copy number variation in key fluconazole resistance genes

We used whole-genome sequencing to analyze a collection of 35 fluconazole-resistant and 7 susceptible Candida parapsilosis isolates together with coverage analysis and GWAS techniques to identify new mechanisms of fluconazole resistance. Phylogenetic analysis shows that although the collection is diverse, two persistent clinical lineages were identified. We identified copy number variation (CNV) of two genes, ERG11 and CDR1B, in resistant isolates. Two strains have a CNV at the ERG11 locus; the entire ORF is amplified in one, and only the promoter region is amplified in the other. We show that the annotated telomeric gene CDR1B is actually an artifactual in silico fusion of two highly similar neighboring CDR genes due to an assembly error in the C. parapsilosis CDC317 reference genome. We report highly variable copy numbers of the CDR1B region across the collection. Several strains have increased the expansion of the two genes into a tandem array of new chimeric genes. Other strains have experienced a deletion between the two genes creating a single gene with a reciprocal chimerism. We find translocations, duplications, and gene conversion across the CDR gene family in the C. parapsilosis species complex, showing that it is a highly dynamic family.

Nonstereotypical Distribution and Effect of Ergosterol in Lipid Membranes

Ergosterol, found in fungi and some protist membranes, is understudied compared with cholesterol from animal membranes. Generally, ergosterol is assumed to modulate membranes in the same manner as cholesterol, based on their similar chemical structures. Here we reveal some fundamental structural and dynamical differences between them. Neutron diffraction shows that ergosterol is embedded in the lipid bilayer much shallower than cholesterol. Ergosterol does not change the membrane thickness as much as cholesterol does, indicating little condensation effect. Neutron spin echo shows that ergosterol can rigidify and soften membranes at different concentrations. The lateral lipid diffusion measured by quasielastic neutron scattering indicates that ergosterol promotes a jump diffusion of the lipid, whereas cholesterol keeps the same continuous lateral diffusion as the pure lipid membrane. Our results point to quite distinct interactions of ergosterol with membranes compared with cholesterol. These insights provide a basic understanding of membranes containing ergosterol with implications for phenomena such as lipid rafts and drug interactions.

Functional study of two ER localized sterol C-14 reductases in Aspergillus oryzae

Ergosterol is an important component of fungal cell membrane. Ergosterol biosynthesis involves sterol C-14 reductase, a key enzyme in ergosterol biosynthesis, which has been well studied in Saccharomyces cerevisiae. However, little studies about this important enzyme in Aspergillus oryzae. In this study, two sterol C-14 reductases named AoErg24A and AoErg24B were identified in A. oryzae using bioinformatics analysis. Through phylogenetic tree, expression pattern, subcellular localization, and yeast functional complementation analyses, we discovered that both AoErg24A and AoErg24B are conserved and localized to the endoplasmic reticulum (ER). Both enzymes can partially restore the temperature sensitivity phenotype of a S. cerevisiae erg24 weak mutant. Overexpression of AoErg24A in A. oryzae increased 1.6 times of ergosterol content, while overexpression of AoErg24B led to a slight decrease of ergosterol. Both genes affect the sporulation of A. oryzae. These results uncovered that the two genes function differently in ergosterol biosynthesis. Thus, this study further enhances our understanding of ergosterol biosynthesis in A. oryzae and lays a good foundation for A. oryzae to be used in industrial ergosterol production.

Functional interplay of lipid droplets and mitochondria

Our body stores energy mostly in form of fatty acids (FAs) in lipid droplets (LDs). From there the FAs can be mobilized and transferred to peroxisomes and mitochondria. This transfer is dependent on close opposition of LDs and mitochondria and peroxisomes and happens at membrane contact sites. However, the composition and the dynamics of these contact sites is not well understood, which is in part due to the dependence on the metabolic state of the cell and on the cell- and tissue-type. Here, we summarize the current knowledge on the contacts between lipid droplets and mitochondria both in mammals and in the yeast Saccharomyces cerevisiae, in which various contact sites are well studied. We discuss possible functions of the contact site and their implication in disease.

Biofilm-associated metabolism via ERG251 in Candida albicans

Biofilm formation by the fungal pathogen Candida albicans is the basis for its ability to infect medical devices. The metabolic gene ERG251 has been identified as a target of biofilm transcriptional regulator Efg1, and here we report that ERG251 is required for biofilm formation but not conventional free-living planktonic growth. An erg251Δ/Δ mutation impairs biofilm formation in vitro and in an in vivo catheter infection model. In both in vitro and in vivo biofilm contexts, cell number is reduced and hyphal length is limited. To determine whether the mutant defect is in growth or some other aspect of biofilm development, we examined planktonic cell features in a biofilm-like environment, which was approximated with sealed unshaken cultures. Under those conditions, the erg251Δ/Δ mutation causes defects in growth and hyphal extension. Overexpression in the erg251Δ/Δ mutant of the paralog ERG25, which is normally expressed more weakly than ERG251, partially improves biofilm formation and biofilm hyphal content, as well as growth and hyphal extension in a biofilm-like environment. GC-MS analysis shows that the erg251Δ/Δ mutation causes a defect in ergosterol accumulation when cells are cultivated under biofilm-like conditions, but not under conventional planktonic conditions. Overexpression of ERG25 in the erg251Δ/Δ mutant causes some increase in ergosterol levels. Finally, the hypersensitivity of efg1Δ/Δ mutants to the ergosterol inhibitor fluconazole is reversed by ERG251 overexpression, arguing that reduced ERG251 expression contributes to this efg1Δ/Δ phenotype. Our results indicate that ERG251 is required for biofilm formation because its high expression levels are necessary for ergosterol synthesis in a biofilm-like environment.

Efficient Plant Triterpenoids Synthesis in Saccharomyces cerevisiae: from Mechanisms to Engineering Strategies

Triterpenoids possess a range of biological activities and are extensively utilized in the pharmaceutical, food, cosmetic, and chemical industries. Traditionally, they are acquired through chemical synthesis and plant extraction. However, these methods have drawbacks, including high energy consumption, environmental pollution, and being time-consuming. Recently, the de novo synthesis of triterpenoids in microbial cell factories has been achieved. This represents a promising and environmentally friendly alternative to traditional supply methods. Saccharomyces cerevisiae, known for its robustness, safety, and ample precursor supply, stands out as an ideal candidate for triterpenoid biosynthesis. However, challenges persist in industrial production and economic feasibility of triterpenoid biosynthesis. Consequently, metabolic engineering approaches have been applied to improve the triterpenoid yield, leading to substantial progress. This review explores triterpenoids biosynthesis mechanisms in S. cerevisiae and strategies for efficient production. Finally, the review also discusses current challenges and proposes potential solutions, offering insights for future engineering.

Deciphering antifungal and antibiofilm mechanisms of isobavachalcone against Cryptococcus neoformans through RNA-seq and functional analyses

Cryptococcus neoformans has been designated as critical fungal pathogens by the World Health Organization, mainly due to limited treatment options and the prevalence of antifungal resistance. Consequently, the utilization of novel antifungal agents is crucial for the effective treatment of C. neoformans infections. This study exposed that the minimum inhibitory concentration (MIC) of isobavachalcone (IBC) against C. neoformans H99 was 8 µg/mL, and IBC dispersed 48-h mature biofilms by affecting cell viability at 16 µg/mL. The antifungal efficacy of IBC was further validated through microscopic observations using specific dyes and in vitro assays, which confirmed the disruption of cell wall/membrane integrity. RNA-Seq analysis was employed to decipher the effect of IBC on the C. neoformans H99 transcriptomic profiles. Real-time quantitative reverse transcription PCR (RT-qPCR) analysis was performed to validate the transcriptomic data and identify the differentially expressed genes. The results showed that IBC exhibited various mechanisms to impede the growth, biofilm formation, and virulence of C. neoformans H99 by modulating multiple dysregulated pathways related to cell wall/membrane, drug resistance, apoptosis, and mitochondrial homeostasis. The transcriptomic findings were corroborated by the antioxidant analyses, antifungal drug sensitivity, molecular docking, capsule, and melanin assays. In vivo antifungal activity analysis demonstrated that IBC extended the lifespan of C. neoformans-infected Caenorhabditis elegans. Overall, the current study unveiled that IBC targeted multiple pathways simultaneously to inhibit growth significantly, biofilm formation, and virulence, as well as to disperse mature biofilms of C. neoformans H99 and induce cell death.

Transcriptome analysis of Kluyveromyces marxianus under succinic acid stress and development of robust strains

Kluyveromyces marxianus has become an attractive non-conventional yeast cell factory due to its advantageous properties such as high thermal tolerance and rapid growth. Succinic acid (SA) is an important platform molecule that has been applied in various industries such as food, material, cosmetics, and pharmaceuticals. SA bioproduction may be compromised by its toxicity. Besides, metabolite-responsive promoters are known to be important for dynamic control of gene transcription. Therefore, studies on global gene transcription under various SA concentrations are of great importance. Here, comparative transcriptome changes of K. marxianus exposed to various concentrations of SA were analyzed. Enrichment and analysis of gene clusters revealed repression of the tricarboxylic acid cycle and glyoxylate cycle, also activation of the glycolysis pathway and genes related to ergosterol synthesis. Based on the analyses, potential SA-responsive promoters were investigated, among which the promoter strength of IMTCP2 and KLMA_50231 increased 43.4% and 154.7% in response to 15 g/L SA. In addition, overexpression of the transcription factors Gcr1, Upc2, and Ndt80 significantly increased growth under SA stress. Our results benefit understanding SA toxicity mechanisms and the development of robust yeast for organic acid production. KEY POINTS: • Global gene transcription of K. marxianus is changed by succinic acid (SA) • Promoter activities of IMTCP2 and KLMA_50123 are regulated by SA • Overexpression of Gcr1, Upc2, and Ndt80 enhanced SA tolerance.

Transcriptomic profiling of an evolved Yarrowia lipolytica strain: tackling hexanoic acid fermentation to increase lipid production from short-chain fatty acids

BACKGROUND

Short-chain fatty acids (SCFAs) are cost-effective carbon sources for an affordable production of lipids. Hexanoic acid, the acid with the longest carbon chain in the SCFAs pool, is produced in anaerobic fermentation of organic residues and its use is very challenging, even inhibiting oleaginous yeasts growth.

RESULTS

In this investigation, an adaptive laboratory evolution (ALE) was performed to improve Yarrowia lipolytica ACA DC 50109 tolerance to high hexanoic acid concentrations. Following ALE, the transcriptomic analysis revealed several genetic adaptations that improved the assimilation of this carbon source in the evolved strain compared to the wild type (WT). Indeed, the evolved strain presented a high expression of the up-regulated gene YALI0 E16016g, which codes for FAT1 and is related to lipid droplets formation and responsible for mobilizing long-chain acids within the cell. Strikingly, acetic acid and other carbohydrate transporters were over-expressed in the WT strain.

CONCLUSIONS

A more tolerant yeast strain able to attain higher lipid content under the presence of high concentrations of hexanoic acid has been obtained. Results provided novel information regarding the assimilation of hexanoic acid in yeasts.

Discovery of New Antimicrobial Metabolites in the Coculture of Medicinal Mushrooms

Bioactivity screening revealed that the antifungal activities of EtOAc extracts from coculture broths of Trametes versicolor SY630 with either Vanderbylia robiniophila SY341 or Ganoderma gibbosum SY1001 were significantly improved compared to that of monocultures. Activity-guided isolation led to the discovery of five aromatic compounds (1-5) from the coculture broth of T. versicolor SY630 and V. robiniophila SY341 and two sphingolipids (6 and 7) from the coculture broth of T. versicolor SY630 and G. gibbosum SY1001. Tramevandins A-C (1-3) and 17-ene-1-deoxyPS (6) are new compounds, while 1-deoxyPS (7) is a new natural product. Notably, compound 2 represents a novel scaffold, wherein the highly modified p-terphenyl bears a benzyl substituent. The absolute configurations of those new compounds were elucidated by X-ray diffraction, ECD calculations, and analysis of physicochemical constants. Compounds 1, 2, and 5-7 exhibited different degrees of antimicrobial activity, and the antifungal activities of compounds 6 and 7 against Candida albicans and Cryptococcus neoformans are comparable to those of fluconazole, nystatin, and sphingosine, respectively. Transcriptome analysis, propidium iodide staining, ergosterol quantification, and feeding assays showed that the isolated sphingolipids can extensively downregulate the late biosynthetic pathway of ergosterol in C. albicans, representing a promising mechanism to combat antibiotic-resistant fungi.

Resistance mechanisms of Saccharomyces cerevisiae against silver nanoparticles with different sizes and coatings

To investigate the underlying resistance mechanisms of Saccharomyces cerevisiae against Ag-NPs with different particle sizes and coatings, transcriptome sequencing (RNA-seq) technology was used to characterize the transcriptomes from S. cerevisiae exposed to 20-PVP-Ag, 100-PVP-Ag, 20-CIT-Ag and 100-CIT-Ag, respectively. The steroid biosynthesis was found as a general pathway for Ag-NPs stress responding, in which ERG6 and ERG3 were inhibited and ERG11, ERG25 and ERG5 were significantly up-regulated to resist the stress by supporting the later mutation and resistance and modulate drug efflux indirectly. The resistance mechanism of S. cerevisiae to 20-PVP-Ag seems different from that of 100-PVP-Ag, 20-CIT-Ag and 100-CIT-Ag. Under the 20-PVP-Ag, transmembrane transporter activity, transition metal ion homeostasis and oxidative phosphorylation pathway were main resistance pathways to enhance cell transport processes. While 100-PVP-Ag, 20-CIT-Ag and 100-CIT-Ag mainly impacted RNA binding, structural constituent of ribosome and ribosome pathway which can provide more energy to maintain the number and function of protein in cells. This study reveals the differences in resistance mechanisms of S. cerevisiae to Ag-NPs with different particle sizes and coatings, and explains several main regulatory mechanisms used to respond to silver stress. It will provide theoretical basis for the study of chemical risk assessment.

Erg251 has complex and pleiotropic effects on azole susceptibility, filamentation, and stress response phenotypes

Ergosterol is essential for fungal cell membrane integrity and growth, and numerous antifungal drugs target ergosterol. Inactivation or modification of ergosterol biosynthetic genes can lead to changes in antifungal drug susceptibility, filamentation and stress response. Here, we found that the ergosterol biosynthesis gene ERG251 is a hotspot for point mutations during adaptation to antifungal drug stress within two distinct genetic backgrounds of Candida albicans. Heterozygous point mutations led to single allele dysfunction of ERG251 and resulted in azole tolerance in both genetic backgrounds. This is the first known example of point mutations causing azole tolerance in C. albicans. Importantly, single allele dysfunction of ERG251 in combination with recurrent chromosome aneuploidies resulted in bona fide azole resistance. Homozygous deletions of ERG251 caused increased fitness in low concentrations of fluconazole and decreased fitness in rich medium, especially at low initial cell density. Dysfunction of ERG251 resulted in transcriptional upregulation of the alternate sterol biosynthesis pathway and ZRT2, a Zinc transporter. Notably, we determined that overexpression of ZRT2 is sufficient to increase azole tolerance in C. albicans. Our combined transcriptional and phenotypic analyses revealed the pleiotropic effects of ERG251 on stress responses including cell wall, osmotic and oxidative stress. Interestingly, while loss of either allele of ERG251 resulted in similar antifungal drug responses, we observed functional divergence in filamentation regulation between the two alleles of ERG251 (ERG251-A and ERG251-B) with ERG251-A exhibiting a dominant role in the SC5314 genetic background. Finally, in a murine model of systemic infection, homozygous deletion of ERG251 resulted in decreased virulence while the heterozygous deletion mutants maintain their pathogenicity. Overall, this study provides extensive genetic, transcriptional and phenotypic analysis for the effects of ERG251 on drug susceptibility, fitness, filamentation and stress responses.

Effect of citric acid on cell membrane structure and function of Issatchenkia terricola WJL-G4

AIMS

This study aimed to investigate the changes of cell membrane structure and function of Issatchenkia terricola under citric acid by performing physiological analysis.

METHODS AND RESULTS

The membrane integrity, surface hydrophobicity, structure, fluidity, apoptosis, and fatty acid methyl esters composition of I. terricola WJL-G4 cells were determined by propidium iodide staining, microbial adhesion to hydrocarbon test, transmission electron microscopy analysis, fluorescence anisotropy, flow cytometry, and gas chromatography-mass, respectively. The results showed that with the increasing of citric acid concentrations, the cell vitality, membrane integrity, and fluidity of I. terricola reduced; meanwhile, apoptosis rate, membrane permeable, hydrophobicity, and ergosterol contents augmented significantly. Compared to control, the activities of Na+, K+-ATPase, and Ca2+, Mg2+-ATPase increased by 3.73-fold and 6.70-fold, respectively, when citric acid concentration increased to 20 g l-1. The cells cracked and their cytoplasm effused when the citric acid concentration reached 80 g l-1.

CONCLUSIONS

I. terricola could successfully adjust its membrane structure and function below 60 g l-1 of citric acid. However, for citric acid concentrations above 80 g l-1, its structure and function were dramatically changed, which might result in reduced functionality.

Amino acid metabolism and MAP kinase signaling pathway play opposite roles in the regulation of ethanol production during fermentation of sugarcane molasses in budding yeast

Sugarcane molasses is one of the main raw materials for bioethanol production, and Saccharomyces cerevisiae is the major biofuel-producing organism. In this study, a batch fermentation model has been used to examine ethanol titers of deletion mutants for all yeast nonessential genes in this yeast genome. A total of 42 genes are identified to be involved in ethanol production during fermentation of sugarcane molasses. Deletion mutants of seventeen genes show increased ethanol titers, while deletion mutants for twenty-five genes exhibit reduced ethanol titers. Two MAP kinases Hog1 and Kss1 controlling the high osmolarity and glycerol (HOG) signaling and the filamentous growth, respectively, are negatively involved in the regulation of ethanol production. In addition, twelve genes involved in amino acid metabolism are crucial for ethanol production during fermentation. Our findings provide novel targets and strategies for genetically engineering industrial yeast strains to improve ethanol titer during fermentation of sugarcane molasses.

Secretory IgA reduced the ergosterol contents of Candida albicans to repress its hyphal growth and virulence

Candida albicans, one of the most prevalent conditional pathogenic fungi, can cause local superficial infections and lethal systemic infections, especially in the immunocompromised population. Secretory immunoglobulin A (sIgA) is an important immune protein regulating the pathogenicity of C. albicans. However, the actions and mechanisms that sIgA exerts directly against C. albicans are still unclear. Here, we investigated that sIgA directs against C. albicans hyphal growth and virulence to oral epithelial cells. Our results indicated that sIgA significantly inhibited C. albicans hyphal growth, adhesion, and damage to oral epithelial cells compared with IgG. According to the transcriptome and RT-PCR analysis, sIgA significantly affected the ergosterol biosynthesis pathway. Furthermore, sIgA significantly reduced the ergosterol levels, while the addition of exogenous ergosterol restored C. albicans hyphal growth and adhesion to oral epithelial cells, indicating that sIgA suppressed the growth of hyphae and the pathogenicity of C. albicans by reducing its ergosterol levels. By employing the key genes mutants (erg11Δ/Δ, erg3Δ/Δ, and erg3Δ/Δ erg11Δ/Δ) from the ergosterol pathway, sIgA lost the hyphal inhibition on these mutants, while sIgA also reduced the inhibitory effects of erg11Δ/Δ and erg3Δ/Δ and lost the inhibition of erg3Δ/Δ erg11Δ/Δ on the adhesion to oral epithelial cells, further proving the hyphal repression of sIgA through the ergosterol pathway. We demonstrated for the first time that sIgA inhibited C. albicans hyphal development and virulence by affecting ergosterol biosynthesis and suggest that ergosterol is a crucial regulator of C. albicans-host cell interactions. KEY POINTS: • sIgA repressed C. albicans hyphal growth • sIgA inhibited C. albicans virulence to host cells • sIgA affected C. albicans hyphae and virulence by reducing its ergosterol levels.