Farnesol induces apoptosis and oxidative stress in the fungal pathogen Penicillium expansum

Antifungal Mechanism of Ruta graveolens Essential Oil: A Colombian Traditional Alternative against Anthracnose Caused by Colletotrichum gloeosporioides

Here, we report for the first time on the mechanisms of action of the essential oil of Ruta graveolens (REO) against the plant pathogen Colletotrichum gloeosporioides. In particular, the presence of REO drastically affected the morphology of hyphae by inducing changes in the cytoplasmic membrane, such as depolarization and changes in the fatty acid profile where straight-chain fatty acids (SCFAs) increased by up to 92.1%. In addition, REO induced changes in fungal metabolism and triggered apoptosis-like responses to cell death, such as DNA fragmentation and the accumulation of reactive oxygen species (ROS). The production of essential enzymes involved in fungal metabolism, such as acid phosphatase, β-galactosidase, β-glucosidase, and N-acetyl-β-glucosaminidase, was significantly reduced in the presence of REO. In addition, C. gloeosporioides activated naphthol-As-BI phosphohydrolase as a mechanism of response to REO stress. The data obtained here have shown that the essential oil of Ruta graveolens has a strong antifungal effect on C. gloeosporioides. Therefore, it has the potential to be used as a surface disinfectant and as a viable replacement for fungicides commonly used to treat anthracnose in the postharvest testing phase.

Total transcriptome response for tyrosol exposure in Aspergillus nidulans

Although tyrosol is a quorum-sensing molecule of Candida species, it has antifungal activity at supraphysiological concentrations. Here, we studied the effect of tyrosol on the physiology and genome-wide transcription of Aspergillus nidulans to gain insight into the background of the antifungal activity of this compound. Tyrosol efficiently reduced germination of conidia and the growth on various carbon sources at a concentration of 35 mM. The growth inhibition was fungistatic rather than fungicide on glucose and was accompanied with downregulation of 2199 genes related to e.g. mitotic cell cycle, glycolysis, nitrate and sulphate assimilation, chitin biosynthesis, and upregulation of 2250 genes involved in e.g. lipid catabolism, amino acid degradation and lactose utilization. Tyrosol treatment also upregulated genes encoding glutathione-S-transferases (GSTs), increased specific GST activities and the glutathione (GSH) content of the cells, suggesting that A. nidulans can detoxify tyrosol in a GSH-dependent manner even though this process was weak. Tyrosol did not induce oxidative stress in this species, but upregulated "response to nutrient levels", "regulation of nitrogen utilization", "carbon catabolite activation of transcription" and "autophagy" genes. Tyrosol may have disturbed the regulation and orchestration of cellular metabolism, leading to impaired use of nutrients, which resulted in growth reduction.

Deciphering the molecular components of the quorum sensing system in the fungus Ophiostoma piceae

IMPORTANCE

This manuscript presents a comprehensive study on the molecular mechanisms triggered by the quorum sensing (QS) molecule farnesol in the biotechnologically relevant fungus Ophiostoma piceae. We present for the first time, using a multiomics approach, an in-depth analysis of the QS response in a saprotroph fungus, detailing the molecular components involved in the response and their possible mechanisms of action. We think that these results are particularly relevant in the knowledge of the functioning of the QS in eukaryotes, as well as for the exploitation of these mechanisms.

Pseudomonas aeruginosa increases the susceptibility of Candida albicans to amphotericin B in dual-species biofilms

BACKGROUND

Biofilms are the leading cause of nosocomial infections and are hard to eradicate due to their inherent antimicrobial resistance. Candida albicans is the leading cause of nosocomial fungal infections and is frequently co-isolated with the bacterium Pseudomonas aeruginosa from biofilms in the cystic fibrosis lung and severe burn wounds. The presence of C. albicans in multispecies biofilms is associated with enhanced antibacterial resistance, which is largely mediated through fungal extracellular carbohydrates sequestering the antibiotics. However, significantly less is known regarding the impact of polymicrobial biofilms on antifungal resistance.

RESULTS

Here we show that, in dual-species biofilms, P. aeruginosa enhances the susceptibility of C. albicans to amphotericin B, an effect that was biofilm specific. Transcriptional analysis combined with gene ontology enrichment analysis identified several C. albicans processes associated with oxidative stress to be differentially regulated in dual-species biofilms, suggesting that P. aeruginosa exerts oxidative stress on C. albicans, likely through the secretion of phenazines. However, the mitochondrial superoxide dismutase SOD2 was significantly down-regulated in the presence of P. aeruginosa. Monospecies biofilms of the sod2Δ mutant were more susceptible to amphotericin B, and the susceptibility of these biofilms was further enhanced by exogenous phenazines.

CONCLUSIONS

We propose that in dual-species biofilms, P. aeruginosa simultaneously induces mitochondrial oxidative stress, while down-regulating key detoxification enzymes, which prevents C. albicans mounting an appropriate oxidative stress response to amphotericin B, leading to fungal cell death. This work highlights the importance of understanding the impact of polymicrobial interactions on antimicrobial susceptibility.

Herbicide 2,4-dichlorophenoxyacetic acid interferes with MAP kinase signaling in Fusarium graminearum and is inhibitory to fungal growth and pathogenesis

Plant hormones are important for regulating growth, development, and plant-pathogen interactions. Some of them are inhibitory to growth of fungal pathogens but the underlying mechanism is not clear. In this study, we found that hyphal growth of Fusarium graminearum was significantly reduced by high concentrations of IAA and its metabolically stable analogue 2,4-dichlorophenoxyacetic acid (2,4-D). Besides inhibitory effects on growth rate, treatments with 2,4-D also caused significant reduction in conidiation, conidium germination, and germ tube growth. Treatments with 2,4-D had no obvious effect on sexual reproduction but significantly reduced TRI gene expression, toxisome formation, and DON production. More importantly, treatments with 2,4-D were inhibitory to infection structure formation and pathogenesis at concentrations higher than 100 µM. The presence of 1000 µM 2,4-D almost completely inhibited plant infection and invasive growth. In F. graminearum, 2,4-D induced ROS accumulation and FgHog1 activation but reduced the phosphorylation level of Gpmk1 MAP kinase. Metabolomics analysis showed that the accumulation of a number of metabolites such as glycerol and arabitol was increased by 2,4-D treatment in the wild type but not in the Fghog1 mutant. Transformants expressing the dominant active FgPBS2S451D T455D allele were less sensitive to 2,4-D and had elevated levels of intracellular glycerol and arabitol induced by 2,4-D in PH-1. Taken together, our results showed that treatments with 2,4-D interfere with two important MAP kinase pathways and are inhibitory to hyphal growth, DON biosynthesis, and plant infection in F. graminearum.

Cyclic Lipopeptides of Bacillus amyloliquefaciens DHA6 Are the Determinants to Suppress Watermelon Fusarium Wilt by Direct Antifungal Activity and Host Defense Modulation

Fusarium wilt, caused by Fusarium oxysporum f. sp. niveum (Fon), poses a serious threat to watermelon productivity. We previously characterized six antagonistic bacterial strains, including DHA6, capable of suppressing watermelon Fusarium wilt under greenhouse conditions. This study investigates the role of extracellular cyclic lipopeptides (CLPs) produced by strain DHA6 in Fusarium wilt suppression. Taxonomic analysis based on the 16S rRNA gene sequence categorized strain DHA6 as Bacillus amyloliquefaciens. MALDI-TOF mass spectrometry identified five families of CLPs, i.e., iturin, surfactin, bacillomycin, syringfactin, and pumilacidin, in the culture filtrate of B. amyloliquefaciens DHA6. These CLPs exhibited significant antifungal activity against Fon by inducing oxidative stress and disrupting structural integrity, inhibiting mycelial growth and spore germination. Furthermore, pretreatment with CLPs promoted plant growth and suppressed watermelon Fusarium wilt by activating antioxidant enzymes (e.g., catalase, superoxide dismutase, and peroxidase) and triggering genes involved in salicylic acid and jasmonic acid/ethylene signaling in watermelon plants. These results highlight the critical roles of CLPs as determinants for B. amyloliquefaciens DHA6 in suppressing Fusarium wilt through direct antifungal activity and modulation of plant defense responses. This study provides a foundation for developing B. amyloliquefaciens DHA6-based biopesticides, serving as both antimicrobial agents and resistance inducers, to effectively control Fusarium wilt in watermelon and other crops.

Myxobacterial Outer Membrane β-1,6-Glucanase Induced the Cell Death of Fusarium oxysporum by Destroying the Cell Wall Integrity

The β-1,6-glucan is the key linker between mannoproteins in the outermost part of the cell wall and β-1,3-glucan/chitin polysaccharide to maintain the rigid structure of the cell wall. The β-1,6-glucanase GluM, which was purified from the fermentation supernatant of Corallococcus sp. EGB, was able to inhibit the germination of Fusarium oxysporum f. sp. cucumerinum conidia at a minimum concentration of 2.0 U/mL (0.08 μg/mL). The survival rates of GluM-treated conidia and monohyphae were 10.4% and 30.7%, respectively, which were significantly lower than that of β-1,3-glucanase treatment (Zymolyase, 20.0 U/mL; equate to 1.0 mg/mL) (72.9% and 73.9%). In contrast to β-1,3-glucanase treatment, the high-osmolarity glycerol (HOG) pathway of F. oxysporum f. sp. cucumerinum cells was activated after GluM treatment, and the intracellular glycerol content was increased by 2.6-fold. Moreover, the accumulation of reactive oxygen species (ROS) in F. oxysporum f. sp. cucumerinum cells after GluM treatment induced apoptosis, but it was not associated with the increased intracellular glycerol content. Together, the results indicate that β-1,6-glucan is a promising target for the development of novel broad-spectrum antifungal agents. IMPORTANCE Phytopathogenic fungi are the most devastating plant pathogens in agriculture, causing enormous economic losses to global crop production. Biocontrol agents have been promoted as replacements to synthetic chemical pesticides for sustainable agriculture development. Cell wall-degrading enzymes (CWDEs), including chitinases and β-1,3-glucanases, have been considered as important armaments to damage the cell wall. Here, we found that F. oxysporum f. sp. cucumerinum is more sensitive to β-1,6-glucanase GluM treatment (0.08 μg/mL) than β-1,3-glucanase Zymolyase (1.0 mg/mL). The HOG pathway was activated in F. oxysporum f. sp. cucumerinum cells after GluM treatment, and the intracellular glycerol content was significantly increased. Moreover, the decomposition of F. oxysporum f. sp. cucumerinum cell wall by GluM induced the burst of intracellular ROS and apoptosis, which eventually leads to cell death. Therefore, we suggest that the β-1,6-glucan of the fungal cell wall may be a better antifungal target compared to the β-1,3-glucan.

Enzymatic and proteomic exploration into the inhibitory activities of lemongrass and lemon essential oils against Botrytis cinerea (causative pathogen of gray mold)

Introduction

Essential oils (EOs) have been demonstrated as efficacious against B. cinerea. However, the underpinning enzymatic and proteomic mechanism for these inhibitory effects is not entirely clear.

Methods

Thus, this study examined the effects of lemon (Le) and lemongrass (Lg) EOs (individually and in combination) against B. cinerea based on enzymatic and proteomic analyses. Proteomics data are available via ProteomeXchange with identifier PXD038894.

Results and discussion

Both EOs (individually and in combination) displayed abilities to induce scavenging as observed with the reduction of H2O2. Measured malondialdehyde (MDA) and superoxide dismutase (SOD) activity were increased in all EOs treated B. cinerea mycelia compared to the control. Ascorbate peroxidase (APX) activity was highest in Lg treated B. cinerea (206% increase), followed by combined (Le + Lg) treatment with 73% compared to the untreated control. Based on GC-MS analysis, the number of volatile compounds identified in lemon and lemongrass EOs were 7 and 10, respectively. Major chemical constituent of lemon EO was d-limonene (71%), while lemongrass EO was a-citral (50.1%). Based on the interrogated LC-MS data, 42 distinct proteins were identified, and 13 of these proteins were unique with 1, 8, and 4 found in Le-, Lg-, and (Le + Lg) EOs treated B. cinerea, respectively, and none in control. Overall, 72% of identified proteins were localized within cellular anatomical entity, and 28% in protein-complexes. Proteins involved in translation initiation, antioxidant activity, protein macromolecule adaptor activity and microtubule motor activity were only identified in the Lg and (Le + Lg) EOs treated B. cinerea mycelia, which was consistent with their APX activities.

Anti-Candida Potential of Sclareol in Inhibiting Growth, Biofilm Formation, and Yeast-Hyphal Transition

Even though Candida albicans commonly colonizes on most mucosal surfaces including the vaginal and gastrointestinal tract, it can cause candidiasis as an opportunistic infectious fungus. The emergence of resistant Candida strains and the toxicity of anti-fungal agents have encouraged the development of new classes of potential anti-fungal agents. Sclareol, a labdane-type diterpene, showed anti-Candida activity with a minimum inhibitory concentration of 50 μg/mL in 24 h based on a microdilution anti-fungal susceptibility test. Cell membrane permeability with propidium iodide staining and mitochondrial membrane potential with JC-1 staining were increased in C. albicans by treatment of sclareol. Sclareol also suppressed the hyphal formation of C. albicans in both liquid and solid media, and reduced biofilm formation. Taken together, sclareol induces an apoptosis-like cell death against Candida spp. and suppressed biofilm and hyphal formation in C. albicans. Sclareol is of high interest as a novel anti-fungal agent and anti-virulence factor.

Microplastic-Induced Oxidative Stress in Metolachlor-Degrading Filamentous Fungus Trichoderma harzianum

While there has been intensive research on the influence of microplastics (MPs) on aquatic organisms and humans, their effect on microorganisms is relatively little-known. The present study describes the response of the Trichoderma harzianum strain to low-density polyethylene (LDPE) microparticles. MPs, either separately or with metolachlor (MET), were added to the cultures. Initially, MP was not found to have a negative effect on fungal growth and MET degradation. After 72 h of cultivation, the content of fungal biomass in samples with MPs was almost three times higher than that in the cultures without MPs. Additionally, a 75% degradation of the initial MET was observed. However, due to the qualitative and quantitative changes in individual classes of phospholipids, cell membrane permeability was increased. Additionally, MPs induced the overproduction of reactive oxygen species. The activity of superoxide dismutase and catalase was also increased in response to MPs. Despite these defense mechanisms, there was enhanced lipid peroxidation in the cultures containing the LDPE microparticles. The results of the study may fill the knowledge gap on the influence of MPs on filamentous fungi. The findings will be helpful in future research on the biodegradation of contaminants coexisting with MPs in soil.

Mechanisms underlying the inhibitory effects of linalool on Aspergillus flavus spore germination

Biogenic volatile organic compounds hold remarkable potential for controlling fungal decay in agro- and food products. Recently, we reported that linalool, the major volatile component of the Zanthoxylum schinifolium pericarp, showed great potential as a biofumigant to control Aspergillus flavus growth in postharvest grains. In this study, the inhibitory effects of linalool on A. flavus growth in stored grains and its underlying mechanism were investigated through transcriptomic and biochemical analyses. Linalool vapor at 800 μL/L can effectively prevent A. flavus growth in 22% moisture wheat grains. Linalool at 2 μL/mL completely inhibited the germination of A. flavus spores, and 10 μL/mL caused spore death. Scanning electron microscopy revealed that linalool treatment caused wrinkling and spore breakage. Transcriptomics showed that 3806 genes were significantly differentially expressed in A. flavus spores exposed to 2 μL/mL linalool, predominantly showing enrichment regarding the ribosome, DNA replication, glutathione metabolism, peroxisome, and MAPK signaling pathways. Flow cytometry showed that linalool treatment caused hyperpolarization of mitochondrial membrane potential. 4,6-Diamidino-2-phenylindole staining indicated that linalool caused DNA fragmentation in A. flavus spores, and monodansylcadaverine staining confirmed that linalool induced autophagy in A. flavus spores. We thus propose that linalool can damage the plasma membrane, cause mitochondrial dysfunction and DNA damage, and induce autophagy in A. flavus spores. These findings considerably improve our understanding of the mechanisms underlying the inhibitory effects of linalool on A. flavus, which is crucial regarding the development of applications to prevent postharvest grain spoilage due to A. flavus infestations. KEY POINTS: • The inhibitory potency of linalool on A. flavus spore germination was determined. • Transcriptomic analyses were performed to identify differentially expressed genes of A. flavus exposed to linalool. • A functional mechanism underlying the inhibitory effects of linalool on A. flavus spore germination is proposed.

An inducible potato (E,E)-farnesol synthase confers tolerance against bacterial pathogens in potato and tobacco

Terpene synthases (TPSs) have diverse biological functions in plants. Though the roles of TPSs in herbivore defense are well established in many plant species, their role in bacterial defense has been scarce and is emerging. Through functional genomics, here we report the in planta role of potato (Solanum tuberosum) terpene synthase (StTPS18) in bacterial defense. Expression of StTPS18 was highest in leaves and was induced in response to Pseudomonas syringae and methyl jasmonate treatments. The recombinant StTPS18 exhibited bona fide (E,E)-farnesol synthase activity forming a sesquiterpenoid, (E,E)-farnesol as the sole product, utilising (E,E)-farnesyl diphosphate (FPP). Subcellular localization of GFP fusion protein revealed that StTPS18 is localized to the cytosol. Silencing and overexpression of StTPS18 in potato resulted in reduced and enhanced tolerance, respectively, to bacterial pathogens P. syringae and Ralstonia solanacearum. Bacterial growth assay using medium containing (E,E)-farnesol significantly inhibited P. syringae growth. Moreover, StTPS18 overexpressing transgenic potato and Nicotiana tabacum leaves, and (E,E)-farnesol and P. syringae infiltrated potato leaves exhibited elevated expression of sterol pathway and members of pathogenesis-related genes with enhanced phytosterol accumulation. Interestingly, enhanced phytosterols in 13 C3 -(E,E)-farnesol infiltrated potato leaves were devoid of any noticeable 13 C labeling, indicating no direct utilization of (E,E)-farnesol in phytosterols formation. Furthermore, leaves of StTPS18 overexpressing transgenic lines had no detectable (E,E)-farnesol similar to the control plant, and emitted lower levels of sesquiterpenes than the control. These findings point towards an indirect involvement of StTPS18 and its product (E,E)-farnesol in bacterial defense through upregulation of phytosterol biosynthesis and defense genes.

Microbe Related Chemical Signalling and Its Application in Agriculture

The agriculture sector has been put under tremendous strain by the world’s growing population. The use of fertilizers and pesticides in conventional farming has had a negative impact on the environment and human health. Sustainable agriculture attempts to maintain productivity, while protecting the environment and feeding the global population. The importance of soil-dwelling microbial populations in overcoming these issues cannot be overstated. Various processes such as rhizospheric competence, antibiosis, release of enzymes, and induction of systemic resistance in host plants are all used by microbes to influence plant-microbe interactions. These processes are largely founded on chemical signalling. Producing, releasing, detecting, and responding to chemicals are all part of chemical signalling. Different microbes released distinct sorts of chemical signal molecules which interacts with the environment and hosts. Microbial chemicals affect symbiosis, virulence, competence, conjugation, antibiotic production, motility, sporulation, and biofilm growth, to name a few. We present an in-depth overview of chemical signalling between bacteria-bacteria, bacteria-fungi, and plant-microbe and the diverse roles played by these compounds in plant microbe interactions. These compounds’ current and potential uses and significance in agriculture have been highlighted.

Antimicrobial Mechanism and Secondary Metabolite Profiles of Biocontrol Agent Streptomyces lydicus M01 Based on Ultra-High-Performance Liquid Chromatography Connected to a Quadrupole Time-of-Flight Mass Spectrometer Analysis and Genome Sequencing

Streptomyces lydicus was used as biopesticide for crop protection in agriculture, however, the antimicrobial mechanism remains unclear and no systematic research on the secondary metabolites of S. lydicus has been reported. In this study, the extract of S. lydicus M01 culture was used to treat plant pathogen Alternaria alternata and morphological changes in the plasma membrane and cell wall of hyphae and conidia were observed. Fluorescence microscopy combined with different dyes showed that the accumulation of reactive oxygen species and cell death were also induced. To investigate the secondary metabolites in the culture filtrate, an online detection strategy of ultra-high-performance liquid chromatography connected to a quadrupole time-of-flight mass spectrometer (UPLC-Q-TOF-MS) was used for identification. The results revealed an excess of 120 metabolites, mainly consisted of fungicides, antibacterial agents, herbicides, insecticides, and plant growth regulators, such as IAA. Among which the five dominant components were oxadixyl, chloreturon, S-metolachlor, fentrazamide, and bucarpolate. On the other hand, the complete genome of S. lydicus M01 was sequenced and a number of key function gene clusters that contribute to the biosynthesis of active secondary metabolites were revealed. This is the first systematic characterization of S. lydicus secondary metabolites, and these results offer novel and valuable evidence for a comprehensive understanding of the biocontrol agent S. lydicus and its application in agriculture.

Ethylene-driven changes in epicuticular wax metabolism in citrus fruit

Epicuticular waxes are important natural compounds that influence cuticle properties and can protect fruit from factors that harm its external quality. We demonstrated that, at a dose that reduces postharvest citrus fruit quality loss (4 d 2 µL L^-1), ethylene redirected epicuticular wax metabolism towards the synthesis of primary alcohols, mostly behenyl alcohol, by favouring the acyl-reduction pathway. This treatment also reduced the synthesis of terpenoids by redirecting the mevalonate pathway towards farnesol accumulation to the detriment of the accumulation of most triterpenoids, but not of their precursor squalene. Moreover, the 4 d ethylene treatment sharply increased the synthesis of docosane and lignoceric acid and lowered that of cerotic acid. Longer ethylene exposure (8 d) reversed some of these effects by lowering the contents of most alcohols, lignoceric acid and squalene, while increasing that of its derivative sitosterol. The 8 d ethylene treatment also increased farnesol and docosane contents.

5-Methoxyindole, a Chemical Homolog of Melatonin, Adversely Affects the Phytopathogenic Fungus Fusarium graminearum

Fusarium graminearum is a destructive fungal pathogen that threatens the production and quality of wheat, and controlling this pathogen is a significant challenge. As the cost-effective homolog of melatonin, 5-methoxyindole showed strong activity against F. graminearum. In the present study, our results showed the strong adverse activity of 5-methoxyindole against F. graminearum by inhibiting its growth, formation, and conidia germination. In addition, 5-methoxyindole could induce malformation, reactive oxygen species (ROS) accumulation, and cell death in F. graminearum hyphae and conidia. In response to 5-methoxyindole, F. graminearum genes involved in scavenging reactive oxygen species were significantly downregulated. Overall, these findings reveal the mechanism of antifungal action of melatonin-homolog 5-methoxyindole. To the best of our knowledge, this is the first report that a novel melatonin homolog confers strong antifungal activity against F. graminearum, and 5-methoxyindole is a potential compound for protecting wheat plants from F. graminearum infection.

Antifungal effects of ZnO, TiO2 and ZnO-TiO2 nanostructures on Aspergillus flavus

This study aimed to synthesis ZnO, TiO₂, and ZnO-TiO₂ (ratio weight of 1/1 for Zn/Ti) nanoparticles using zinc acetate and titanium isopropoxide through the sol-gel method. Physicochemical and morphological characterization and antifungal properties evaluation like minimum inhibition concentration (MIC) and minimum fungicide concentration (MFC) of nanopowders were investigated against A.flavus in vitro. All synthesized nanoparticles (50 μg/ml) showed fungal growth inhibition, while ZnO-TiO₂ showed higher antifungal activity against A. flavus than pure TiO₂ and ZnO. TiO₂ and ZnO-TiO₂ (300 μg/ml) inhibited 100% of spur production. Pure ZnO and TiO₂ showed pyramidal and spherical shapes, respectively, whereas ZnO-TiO₂ nanopowders illustrated both spherical and pyramidal shapes with grown particles on the surface. Based on our findings, a low concentration (150 μg/ml) of ZnO-TiO₂ showed higher ROS production and oxidative stress induction, thus the fungicide effect as compared to alone TiO₂ and ZnO. In conclusion, ZnO-TiO₂ nanostructure can be utilized as a useful antifungal compound, but more studies need to be performed to understand the antifungal mechanism of the nanoparticles rather than ROS inducing apoptosis.

Chlorogenic acid induces ROS-dependent apoptosis in Fusarium fujikuroi and decreases the postharvest rot of cherry tomato

Chlorogenic acid is a plant polyphenol with antioxidant and antimicrobial activities. Fusarium fujikuroi is a fungal pathogen that causes many vegetables and fruits, including tomato, to rot. The effects of chlorogenic acid on the development of Fusarium rot of cherry tomato fruit were examined in the present study. Results showed that conidial germination, germ tube elongation, cell viability, and mycelial growth of F. fujikuroi were all significantly inhibited by chlorogenic acid. Chlorogenic acid stimulated the accumulation of reactive oxygen species (ROS), leading to cell apoptosis in F. fujikuroi. The addition of N-acetylcysteine partially recovered the mycelial growth, implying the antifungal activity of chlorogenic acid is related to a ROS burst. The application of chlorogenic acid decreased disease incidence and severity in cherry tomato fruit in a concentration-dependent manner. Taken together, these results suggest that chlorogenic acid inhibits the postharvest rot of cherry tomato fruit caused by F. fujikuroi by inducing cellular oxidative stress in the pathogen.

The Role of Intestinal Fungi and Its Metabolites in Chronic Liver Diseases

Current studies have confirmed that liver diseases are closely related to intestinal microorganisms; however, those studies have mainly concentrated on bacteria. Although the proportion of intestinal microorganisms accounted for by colonizing fungi is very small, these fungi do have a significant effect on the homeostasis of the intestinal microecosystem. In this paper, the characteristics of intestinal fungi in patients with chronic liver diseases such as alcoholic liver disease, nonalcoholic fatty liver disease and cirrhosis are summarized, and the effects of intestinal fungi and their metabolites are analyzed and discussed. It is important to realize that not only bacteria but also intestinal fungi play important roles in liver diseases.

Volatile Organic Compound-Mediated Antifungal Activity of Pichia spp. and Its Effect on the Metabolic Profiles of Fermentation Communities

Volatile organic compounds (VOCs) are chemicals responsible for antagonistic activity between microorganisms. The impact of VOCs on microbial community succession of fermentation is not well understood. In this study, Pichia spp. were evaluated for VOC production as a part of antifungal activity during baijiu fermentation. The results showed that the abundance of Pichia in the defect group (agglomerated fermented grains) was lower than that in control group, and a negative interaction between Pichia and Monascus was determined (P < 0.05). In addition, the disruption of fungi was significantly related to the differences of metabolic profiles in fermented grains. To determine production of VOCs from Pichia and its effect on Monascus purpureus, a double-dish system was assessed, and the incidence of M. purpureus reduction was 39.22% after 7 days. As to antifungal volatile compounds, 2-phenylethanol was identified to have an antifungal effect on M. purpureus through contact and noncontact. To further confirm the antifungal activity of 2-phenylethanol, scanning electron microscopy showed that 2-phenylethanol widely and significantly inhibited conidium germination and mycelial growth of filamentous fungi. Metatranscriptomic analysis revealed that the Ehrlich pathway is the metabolic path of 2-phenylethanol in Pichia and identified potential antifungal mechanisms, including protein synthesis and DNA damage. This study demonstrated the role of volatile compound-mediated microbial interaction in microbiome assembly and discovered a plausible scenario in which Pichia antagonized fungal blooms. The results may improve the niche establishment and growth of the functional yeast that enhances the flavor of baijiu.IMPORTANCE Fermentation of food occurs within communities of interacting species. The importance of microbial interactions in shaping microbial structure and metabolic performance to optimize the traditional fermentation process has long been emphasized, but the interaction mechanisms remain unclear. This study applied metabolome analysis and amplicon sequencing along with metatranscriptomic analysis to examine the volatile organic compound-mediated antifungal activity of Pichia and its effect on the metabolism of ethanol during baijiu fermentation, potentially enhancing the establishment of the fermentation niche and improving ethanol metabolism.

Fungal Quorum-Sensing Molecules: A Review of Their Antifungal Effect against Candida Biofilms

The number of effective therapeutic strategies against biofilms is limited; development of novel therapies is urgently needed to treat a variety of biofilm-associated infections. Quorum sensing is a special form of microbial cell-to-cell communication that is responsible for the release of numerous extracellular molecules, whose concentration is proportional with cell density. Candida-secreted quorum-sensing molecules (i.e., farnesol and tyrosol) have a pivotal role in morphogenesis, biofilm formation, and virulence. Farnesol can mediate the hyphae-to-yeast transition, while tyrosol has the opposite effect of inducing transition from the yeast to hyphal form. A number of questions regarding Candida quorum sensing remain to be addressed; nevertheless, the literature shows that farnesol and tyrosol possess remarkable antifungal and anti-biofilm effect at supraphysiological concentration. Furthermore, previous in vitro and in vivo data suggest that they may have a potent adjuvant effect in combination with certain traditional antifungal agents. This review discusses the most promising farnesol- and tyrosol-based in vitro and in vivo results, which may be a foundation for future development of novel therapeutic strategies to combat Candida biofilms.

Gut Mycobiota and Fungal Metabolites in Human Homeostasis

BACKGROUND

Accumulating evidence suggests that microbiota play an important role in host's homeostasis. Thus far, researchers have mostly focused on the role of bacterial microbiota. However, human gut is a habitat for several fungal species, which produce numerous metabolites. Furthermore, various types of food and beverages are rich in a wide spectrum of fungi and their metabolites.

METHODS

We searched PUBMED and Google Scholar databases to identify clinical and pre-clinical studies on fungal metabolites, composition of human mycobiota and fungal dysbiosis.

RESULTS

Fungal metabolites may serve as signaling molecules and exert significant biological effects including trophic, anti-inflammatory or antibacterial actions. Finally, research suggests an association between shifts in gut fungi composition and human health. Changes in mycobiota composition have been found in obesity, hepatitis and inflammatory bowel diseases.

CONCLUSION

The influence of mycobiota and dietary fungi on homeostasis in mammals suggests a pharmacotherapeutic potential of modulating the mycobiota which may include treatment with probiotics and fecal transplantation. Furthermore, antibacterial action of fungi-derived molecules may be considered as a substitution for currently used antibacterial agents and preservatives in food industry.

Sexual attraction: a review of bumblebee male pheromones

Males of many bumblebee species exhibit a conspicuous pre-mating behavior with two distinct behavioral components: scent marking and patrol flying. The marking pheromone is produced by the cephalic part of the labial gland (CLG). As far as is known, the CLG secretion is species specific, and it usually consists of two types of compounds: (i) straight-chain aliphatic alcohols, aldehydes or esters, and (ii) acyclic mono-, sesqui- and diterpenes (alcohols or acetates). Here, we summarize data from the literature reporting chemical composition of the CLG secretions of more than 80 bumblebee species. Similarities and differences within and between subgenera are discussed in the context of biosynthetic pathways and evolution.

Changes in Cuticle Components and Morphology of 'Satsuma' Mandarin (Citrus unshiu) during Ambient Storage and Their Potential Role on Penicillium digitatum Infection

To elucidate the role of fruit cuticle in fungal infection, changes in cuticle composition and morphology of 'Satsuma' mandarin during ambient (at 25 °C) storage and their role in Penicillium digitatum infection were investigated. Results showed that the epicuticular wax yield increased from 1.11 μg cm-2 to 4.21 μg cm-2 during storage for 20 days and then decreased to 1.35 μg cm-2 as storage time prolonged to 40 days. Intracuticular wax content of fruits stored for 20 days showed a peak value that was 1.7-fold higher than that of fruits stored for 40 days. The contents of cutin monomers of fruits showed a decreased trend during storage, while their proportions in the cutin stayed stable. Acids were identified as the most abundant components in epicuticular wax independently of the storage time, followed by alkanes and terpenoids. Terpenoids were found as the predominant components in intracuticular wax during the whole storage, followed by alkanes and acids. The flattened platelets crystals of fruits at harvest changed into small granule-like wax ones after 10 days of storage then gradually distributed across the surface of the fruits as stored for 40 days. Results of in vitro tests showed that mycelial growth of Penicillium digitatum could be promoted by epicuticular wax and conidial germination could be inhibited by cutin at different storage stages. These results shed new light on the chemical basis for cuticle involvement in fungal infection.

Assessment of oxidative stress and phospholipids alterations in chloroacetanilides-degrading Trichoderma spp

To investigate the induction of oxidative stress and antioxidant response in the chloroacetanilides-degrading Trichoderma spp. under alachlor and metolachlor exposure, a comparative analysis using popular biomarkers was employed. An increased intracellular level of reactive oxygen species (ROS; especially superoxide anion [O₂^-]) as well as products of lipid and protein oxidation after 24 h incubation with the herbicides confirmed chloroacetanilide-induced oxidative stress in tested Trichoderma strains. However, the considerable decline in the ROS levels and the carbonyl group content (biomarkers of protein peroxidation) in a time-dependent manner and changes in the antioxidant enzyme activities indicated an active response against chloroacetanilide-induced oxidative stress and the mechanism of tolerance in tested fungi. Moreover, the tested herbicides clearly modified the phospholipids (PLs) content in Trichoderma spp. in the stationary phase of growth, which was manifested through the difference in phosphatidic acid (PA), phosphatidylethanolamine (PE) and phosphatidylcholines (PC) levels. Despite enhanced lipid peroxidation and changes in PLs in most tested fungi, only a slight modification in membrane integrity of Trichoderma spp. under chloroacetanilides exposure was noted. The obtained results suggest that the alterations in the antioxidant system and the PLs profile of Trichoderma spp. might be useful biomarkers of chloroacetanilide-induced oxidative stress.

The ability of farnesol to prevent adhesion and disrupt Fusarium keratoplasticum biofilm

A biofilm is represented by a community of microorganisms capable of adhering to a surface and producing substances that envelop the cells, forming an extracellular matrix. The extracellular matrix is responsible for protecting microorganisms against environmental stress, hosts the immune system and confers resistance to antimicrobials. Fusarium keratoplasticum is a common species of FSSC (Fusarium solani species complex) associated with human infections, being the most prevalent species related to biofilm formation in hospital water systems and internal pipelines. With this in mind, this study aimed to characterise the biofilm formed by the fungus F. keratoplasticum and to evaluate the effects of farnesol, a fungal quorum sensing (QS) molecule, on the preformed biofilm and also during its formation at different times (adhesion and 24, 48 and 72 h). F. keratoplasticum is able to adhere to an abiotic surface and form a dense biofilm in 72 h, with increased total biomass and matrix modulation with the presence of extracellular DNA, RNA, polysaccharides and proteins. Farnesol exhibited important anti-biofilm activity, causing the destruction of hyphae and the extracellular matrix in preformed biofilm and preventing the adhesion of conidia, filamentation and the formation of biofilm. Few studies have characterised the formation of biofilm by filamentous fungi. Our findings suggest that farnesol acts efficiently on F. keratoplasticum biofilm since this molecule is capable of breaking the extracellular matrix, thereby disarranging the biofilm.

Oxidative Stress and Apoptosis of Gaeumannomyces graminis (Get) Induced by Carabrone

Carabrone is isolated from Carpesium macrocephalum Franch. et Sav, which has good fungicidal activity, especially for Gaeumannomyces graminis (Get). According to previous studies, we speculated that carabrone targets the mitochondrial enzyme complex III of Get. To elucidate the mode of action, we used carabrone to induce oxidative stress and apoptosis in Get. Incubation with carabrone reduced the burst of reactive oxygen species (ROS) and mitochondrial membrane potential, as well as phosphatidylserine release. Carabrone caused ROS accumulation in mycelia by inhibiting the activity of antioxidase enzymes, among which inhibition of glutathione reductase (GR) activity was most obvious. The catalytic center of GR consists of l-cysteine residues that react with the α-methylene-γ-butyrolactone active site of carabrone. Additionally, a positive TUNEL reaction led to diffusion of the DNA electrophoresis band and upregulation of Ggmet1 and Ggmet2. We propose that carabrone inhibits antioxidant enzymes and promotes ROS overproduction, which causes membrane hyperpermeability, release of apoptotic factors, activation of the mitochondria-mediated apoptosis pathway, and fungal cell apoptosis.

Farnesol altered morphogenesis and induced oxidative burst-related responses in Rhizoctonia solani AG1-IA

Farnesol induces morphological changes characteristic of apoptosis in filamentous fungi. Growth-inhibitory effect and induced features of apoptosis on Rhizoctonia solani AG1-IA were observed in our study by addition of exogenous farnesol to the culture. The obtained results implied that farnesol triggered apoptosis-like features, such as production of reactive oxygen species (ROS), in R. solani AG1-IA and that there was increased superoxide dismutase (SOD) activity in the presence of farnesol, as well as decreased fungal biomass. Light microscopic analysis showed that farnesol disrupted the cytoplasm and deformed the hyphae of R. solani AG1-IA. The diameter of the hyphal cross-section in the fungus treated with farnesol decreased compared with control. Transmission electron microscopy (TEM) showed marked alternations in the cell wall, cell membrane, parenthesome, septum, and septal pore of the fungal cells. The findings of this work suggest that farnesol is deleterious to R. solani and has potential for use as an antifungal compound against this destructive phytopathogenic fungus.

Assessment of lead tolerance in gamma exposed Aspergillus niger van Tieghem & Penicillium cyclopium Westling

Purpose: Present study deals with the role of gamma irradiation in modulating lead (Pb) tolerance of Aspergillus niger van Tieghem. and Penicillium cyclopium Westling. Materials and methods: After being exposed to gamma absorbed doses those fungal strains were subjected to heavy metal uptake efficacies and anti-oxidative study. Fourier Transform Infrared (FTIR) spectra and Scanning Electron Microscopic (SEM) studies were also evaluated. Result: Gamma exposed A. niger & P. cyclopium showed enhanced growth in terms of colony forming unit (CFU) and more Pb uptake efficacies compared to their un-irradiated counterparts. FTIR spectra illustrated the involvement of functional groups in Pb biosorption. SEM photographs revealed the structural deformities in both the fungal strains after being exposed to Pb and gamma. Upregulated anti-oxidative defense system (super oxide dismutase, catalase, total glutathione) in gamma exposed fungal groups are accountable for enhanced Pb tolerance and removal than that of their un-irradiated counterparts. Conclusion: The outcomes of this study exhibit a light towards a new step of heavy metal bioremediation.

Antifungal Activity of Chitosan Nanoparticles Encapsulated With Cymbopogon martinii Essential Oil on Plant Pathogenic Fungi Fusarium graminearum

Application of synthetic fungicides in agricultural commodities has been restricted due to development of fungicide resistance fungi and deleterious impact on environment and health of farm animals and humans. Hence, there is an urge for development of mycobiocides, and the present study was undertaken to determine the antifungal activity of Cymbopogon martinii essential oil (CMEO) on post-harvest pathogen Fusarium graminearum. The CMEO was extracted by hydrodistillation and GC-MS chemical profile revealed the presence of 46 compounds and abundant was geraniol (19.06%). The minimum inhibitory concentration and minimum fungicidal concentration of CMEO were determined as 421.7 ± 27.14 and 618.3 ± 79.35 ppm, respectively. The scanning electron microscopic observation of CMEO exposed macroconidia was exhibited a detrimental morphology with vesicles, craters, protuberance, and rough surfaces related to control fungi. The CMEO induced the death of fungi through elevating intracellular reactive oxygen species and lipid peroxidation, and depleting ergosterol content. Regrettably, essential oils are highly volatile and become unstable and lose their biological features on exposure to light, heat, pH, moisture, and oxygen. To overcome these issues, chitosan encapsulated CMEO nanoparticles (Ce-CMEO-NPs) were prepared. The synthesized Ce-CMEO-NPs have spherical morphology with Zeta potential of 39.3-37.2 mV and their corresponding size was found in range of 455-480 nm. The Fourier transform infrared analysis confirmed that bio-active constituents of CMEO were well stabilized due to chitosan conjugation and successfully formed Ce-CMEO-NPs. The in vitro release assay observed that the release of CMEO is stabilized due to the complex formation with chitosan and thereby, increases the lifetime antifungal activity of CMEO by gradual release of antifungal constituents of Ce-CMEO-NPs. In conclusion, antifungal and antimycotoxin activities of CMEO and Ce-CMEO-NPs against F. graminearum were assessed in maize grains under laboratory conditions over a storage period of 28 days. Interestingly, Ce-CMEO-NPs were presented efficient and enhanced antifungal and antimycotoxin activities related to CMEO, and it could be due to perseverance of antifungal activity by controlled release of antifungal constituents from Ce-CMEO-NPs. The study concluded that Ce-CMEO-NPs could be highly appropriate as mycobiocides in safeguarding the agricultural commodities during storage period in agricultural and food industries.

New approaches in bioprocess-control: Consortium guidance by synthetic cell-cell communication based on fungal pheromones

Bioconversions in industrial processes are currently dominated by single-strain approaches. With the growing complexity of tasks to be carried out, microbial consortia become increasingly advantageous and eventually may outperform single-strain fermentations. Consortium approaches benefit from the combined metabolic capabilities of highly specialized strains and species, and the inherent division of labor reduces the metabolic burden for each strain while increasing product yields and reaction specificities. However, consortium-based designs still suffer from a lack of available tools to control the behavior and performance of the individual subpopulations and of the entire consortium. Here, we propose to implement novel control elements for microbial consortia based on artificial cell-cell communication via fungal mating pheromones. Coupling to the desired output is mediated by pheromone-responsive gene expression, thereby creating pheromone-dependent communication channels between different subpopulations of the consortia. We highlight the benefits of artificial communication to specifically target individual subpopulations of microbial consortia and to control e.g. their metabolic profile or proliferation rate in a predefined and customized manner. Due to the steadily increasing knowledge of sexual cycles of industrially relevant fungi, a growing number of strains and species can be integrated into pheromone-controlled sensor-actor systems, exploiting their unique metabolic properties for microbial consortia approaches.

Guidelines and recommendations on yeast cell death nomenclature

Elucidating the biology of yeast in its full complexity has major implications for science, medicine and industry. One of the most critical processes determining yeast life and physiology is cel-lular demise. However, the investigation of yeast cell death is a relatively young field, and a widely accepted set of concepts and terms is still missing. Here, we propose unified criteria for the defi-nition of accidental, regulated, and programmed forms of cell death in yeast based on a series of morphological and biochemical criteria. Specifically, we provide consensus guidelines on the differ-ential definition of terms including apoptosis, regulated necrosis, and autophagic cell death, as we refer to additional cell death rou-tines that are relevant for the biology of (at least some species of) yeast. As this area of investigation advances rapidly, changes and extensions to this set of recommendations will be implemented in the years to come. Nonetheless, we strongly encourage the au-thors, reviewers and editors of scientific articles to adopt these collective standards in order to establish an accurate framework for yeast cell death research and, ultimately, to accelerate the pro-gress of this vibrant field of research.

White rot fungi and advanced combined biotechnology with nanomaterials: promising tools for endocrine-disrupting compounds biotransformation

Endocrine-disrupting compounds (EDCs) can interfere with endocrine systems and bio-accumulate through the food chain and even decrease biodiversity in contaminated areas. This review discusses a critical overview of recent research progress in the biotransformation of EDCs (including polychlorinated biphenyl and nonylphenol, and suspected EDCs such as heavy metals and sulfonamide antibiotics) by white rot fungi (WRF) based on techniques with an emphasis on summarizing and analyzing fungal molecular, metabolic and genetic mechanisms. Not only intracellular metabolism which seems to perform essential roles in the ability of WRF to transform EDCs, but also advanced applications are deeply discussed. This review mainly reveals the removal pathway of heavy metal and antibiotic pollutants because the single pollution almost did not exist in a real environment while the combined pollution has become more serious and close to people's life. The trends in WRF technology and its related advanced applications which use the combined technology, including biocatalysis of WRF and adsorption of nanomaterials, to degrade EDCs have also been introduced. Furthermore, challenges and future research needs EDCs biotransformation by WRF are also discussed. This research, referring to metabolic mechanisms and the combined technology of WRF with nanomaterials, undoubtedly contributes to the applications of biotechnology. This review will be of great benefit to an understanding of the trends in biotechnology for the removal of EDCs.

The Human Mucosal Mycobiome and Fungal Community Interactions

With the advent of high-throughput sequencing techniques, the astonishing extent and complexity of the microbial communities that reside within and upon us has begun to become clear. Moreover, with advances in computing and modelling methods, we are now beginning to grasp just how dynamic our interactions with these communities are. The diversity of both these communities and their interactions—both within the community and with us—are dependent on a multitude of factors, both microbial- and host-mediated. Importantly, it is becoming clear that shifts in the makeup of these communities, or their responses, are linked to different disease states. Although much of the work to define these interactions and links has been investigating bacterial communities, recently there has been significant growth in the body of knowledge, indicating that shifts in the host fungal communities (mycobiome) are also intimately linked to disease status. In this review, we will explore these associations, along with the interactions between fungal communities and their human and microbial habitat, and discuss the future applications of systems biology in determining their role in disease status.

Bacillomycin D Produced by Bacillus amyloliquefaciens Is Involved in the Antagonistic Interaction with the Plant-Pathogenic Fungus Fusarium graminearum

Fusarium graminearum (teleomorph: Ascomycota, Hypocreales, Gibberella, Gibberella zeae) is a destructive fungal pathogen that threatens the production and quality of wheat and barley worldwide. Controlling this toxin-producing pathogen is a significant challenge. In the present study, the commercially available strain Bacillus amyloliquefaciens (Bacteria, Firmicutes, Bacillales, Bacillus) FZB42 showed strong activity against F. graminearum The lipopeptide bacillomycin D, produced by FZB42, was shown to contribute to the antifungal activity. Purified bacillomycin D showed strong activity against F. graminearum, and its 50% effective concentration was determined to be approximately 30 μg/ml. Analyses using scanning and transmission electron microscopy revealed that bacillomycin D caused morphological changes in the plasma membranes and cell walls of F. graminearum hyphae and conidia. Fluorescence microscopy combined with different dyes showed that bacillomycin D induced the accumulation of reactive oxygen species and caused cell death in F. graminearum hyphae and conidia. F. graminearum secondary metabolism also responded to bacillomycin D challenge, by increasing the production of deoxynivalenol. Biological control experiments demonstrated that bacillomycin D exerted good control of F. graminearum on corn silks, wheat seedlings, and wheat heads. In response to bacillomycin D, F. graminearum genes involved in scavenging reactive oxygen species were downregulated, whereas genes involved in the synthesis of deoxynivalenol were upregulated. Phosphorylation of MGV1 and HOG1, the mitogen-activated protein kinases of F. graminearum, was increased in response to bacillomycin D. Taken together, these findings reveal the mechanism of the antifungal action of bacillomycin D.IMPORTANCE Biological control of plant disease caused by Fusarium graminearum is desirable. Bacillus amyloliquefaciens FZB42 is a representative of the biocontrol bacterial strains. In this work, the lipopeptide bacillomycin D, produced by FZB42, showed strong fungicidal activity against F. graminearum Bacillomycin D caused morphological changes in the plasma membrane and cell wall of F. graminearum, induced accumulation of reactive oxygen species, and ultimately caused cell death in F. graminearum Interestingly, when F. graminearum was challenged with bacillomycin D, the deoxynivalenol production, gene expression, mitogen-activated protein kinase phosphorylation, and pathogenicity of F. graminearum were significantly altered. These findings clarified the mechanisms of the activity of bacillomycin D against F. graminearum and highlighted the potential of B. amyloliquefaciens FZB42 as a biocontrol agent against F. graminearum.

Estrogen-mediated protection of the organotin-degrading strain Metarhizium robertsii against oxidative stress promoted by monobutyltin

Dibutyltin (DBT) is a global pollutant characterized by pro-oxidative properties. The fungal strain Metarhizium robertsii can eliminate high levels of DBT efficiently. In this study, induction of oxidative stress as well as its alleviation through the application of natural estrogens during the elimination of DBT by M. robertsii were evaluated. During the first 24 h of incubation, the initial concentration of DBT (20 mg l^-1) was reduced to 3.1 mg l^-1, with simultaneous formation of a major byproduct - monobutyltin (MBT). In the presence of estrone (E1) or 17β-estradiol (E2), the amounts of dibutyltin residues in the fungal cultures were found to be approximately 2-fold higher compared to cultures without estrogens, which was associated with the simultaneous utilization of the compounds by cytochrome P450 enzymes. On the other hand, MBT levels were approximately 2.5 times lower in the fungal cultures with the addition of one of the estrogens. MBT (not DBT) promotes the generation of O₂^-, H₂O₂, and NO at levels 65.89 ± 18.08, 4.04 ± 3.62, and 27.92 ± 1.95, respectively. Superoxide dismutase and catalase activities did not show any response of the M. robertsii strain against the overproduction of superoxide anion and hydrogen peroxide. Application of E1 as well as E2 ensured non-enzymatic defense against nitrosative and oxidative stress through scavenging of nitrogen and oxygen reactive species, and limited their levels from 1.5-fold to 21-fold, depending on the used estrogen.

Regulated Forms of Cell Death in Fungi

Cell death occurs in all domains of life. While some cells die in an uncontrolled way due to exposure to external cues, other cells die in a regulated manner as part of a genetically encoded developmental program. Like other eukaryotic species, fungi undergo programmed cell death (PCD) in response to various triggers. For example, exposure to external stress conditions can activate PCD pathways in fungi. Calcium redistribution between the extracellular space, the cytoplasm and intracellular storage organelles appears to be pivotal for this kind of cell death. PCD is also part of the fungal life cycle, in which it occurs during sexual and asexual reproduction, aging, and as part of development associated with infection in phytopathogenic fungi. Additionally, a fungal non-self-recognition mechanism termed heterokaryon incompatibility (HI) also involves PCD. Some of the molecular players mediating PCD during HI show remarkable similarities to major constituents involved in innate immunity in metazoans and plants. In this review we discuss recent research on fungal PCD mechanisms in comparison to more characterized mechanisms in metazoans. We highlight the role of PCD in fungi in response to exogenic compounds, fungal development and non-self-recognition processes and discuss identified intracellular signaling pathways and molecules that regulate fungal PCD.

Farnesol inhibits translation to limit growth and filamentation in C. albicans and S. cerevisiae

Candida albicans is a polymorphic yeast where the capacity to switch between yeast and filamentous growth is critical for pathogenicity. Farnesol is a quorum-sensing sesquiterpene alcohol that, via regulation of specific signalling and transcription components, inhibits filamentous growth in Candida albicans. Here we show that farnesol also inhibits translation at the initiation step in both Candida albicans and S. cerevisiae. In contrast to fusel alcohols, that target the eukaryotic initiation factor 2B (eIF2B), farnesol affects the interaction of the mRNA with the small ribosomal subunit leading to reduced levels of the 48S preinitiation ribosomal complex in S. cerevisiae. Therefore, farnesol targets a different step in the translation pathway than fusel alcohols to elicit a completely opposite physiological outcome by negating filamentous growth.

Regulation of Isoprenoid Pheromone Biosynthesis in Bumblebee Males

Males of the closely related species Bombus terrestris and Bombus lucorum attract conspecific females by completely different marking pheromones. MP of B. terrestris and B. lucorum pheromones contain mainly isoprenoid (ISP) compounds and fatty acid derivatives, respectively. Here, we studied the regulation of ISP biosynthesis in both bumblebees. RNA-seq and qRT-PCR analyses indicated that acetoacetyl-CoA thiolase (AACT), 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), and farnesyl diphosphate synthase (FPPS) transcripts are abundant in the B. terrestris labial gland. Maximal abundance of these transcripts correlated well with AACT enzymatic activity detected in the LG extracts. In contrast, transcript abundances of AACT, HMGR, and FPPS in B. lucorum were low, and AACT activity was not detected in LGs. These results suggest that transcriptional regulation plays a key role in the control of ISP biosynthetic gene expression and ISP pheromone biosynthesis in bumblebee males.

Efficient alachlor degradation by the filamentous fungus Paecilomyces marquandii with simultaneous oxidative stress reduction

The acceleration of alachlor degradation by Paecilomyces marquandii under controlled and optimized conditions of fungal cultivation in liquid batches was observed (by ca. 20% in comparison to the flask cultures). Acidic environment and oxygen limitation resulted in deterioration of herbicide elimination. Efficient xenobiotic degradation did not correlate with free radicals formation, but some conditions of bioreactor cultivation such as neutral pH and oxygen enriched atmosphere (pO2⩾30%) caused a decrease in the reactive oxygen species (ROS) accumulation in mycelia. The changes in the glutathione (GSH) and ascorbic acid (AA) levels, also in the dismutase (SOD) and catalase (CAT) activities showed active response of the tested fungus against alachlor induced oxidative stress. These results will contribute to the improvement of chloroacetanilides elimination by fungi and extend the knowledge concerning oxidative stress induction and fungal cellular defense.

Effect of Trans, Trans-Farnesol on Pseudogymnoascus destructans and Several Closely Related Species

Bat white-nose syndrome, caused by the psychrophilic fungus Pseudogymnoascus destructans, has dramatically reduced the populations of many hibernating North American bat species. The search for effective biological control agents targeting P. destructans is of great importance. We report that the sesquiterpene trans, trans-farnesol, which is also a Candida albicans quorum sensing compound, prevented in vitro conidial germination for at least 14 days and inhibited growth of preexisting hyphae of five P. destructans isolates in filtered potato dextrose broth at 10 °C. Depending on the inoculation concentrations, both spore and hyphal inhibition occurred upon exposure to concentrations as low as 15-20 µM trans, trans-farnesol. In contrast, most North American Pseudogymnoascus isolates were more tolerant to the exposure of trans, trans-farnesol. Our results suggest that some Candida isolates may have the potential to inhibit the growth of P. destructans and that the sesquiterpene trans, trans-farnesol has the potential to be utilized as a biological control agent.

The Bax inhibitor MrBI-1 regulates heat tolerance, apoptotic-like cell death, and virulence in Metarhizium robertsii

Bax inhibitor 1 (BI-1) is a highly conserved protein originally identified as a suppressor of the proapoptotic protein Bax to inhibit cell death in animals and plants. The orthologs of BI-1 are widely distributed in filamentous fungi but their functions remain largely unknown. Herein, we report the identification and characterizations of MrBI-1, an ortholog of BI-1, in the entomopathogenic fungus Metarhizium robertsii. First, we found that MrBI-1 could partially rescue mammalian Bax-induced cell death in yeast. Deletion of MrBI-1 impaired fungal development, virulence and heat tolerance in M. robertsii. We also demonstrated that inactivation of MrBI-1 reduced fungal resistance to farnesol but not to hydrogen peroxide, suggesting that MrBI-1 contributes to antiapoptotic-like cell death via the endoplasmic reticulum stress-signaling pathway rather than the classical mitochondrium-dependent pathway. In particular, we found that unlike the observations in yeasts and plants, expression of mammalian Bax did not lead to a lethal effect in M. robertsii; however, it did aggravate the fungal apoptotic effect of farnesol. The results of this study advance our understanding of BI-1-like protein functions in filamentous fungi.

Mechanisms of action for 2-phenylethanol isolated from Kloeckera apiculata in control of Penicillium molds of citrus fruits

BACKGROUND

Green and blue mold decay, caused by Penicillium digitatum and P. italicum, respectively, are important postharvest diseases of citrus. Biocontrol by microbes is an alternative to synthetic fungicide application. In this study, the antagonistic yeast strain Kloeckera apiculata 34-9 was used to investigate the action mechanisms involved in the biocontrol of postharvest diseases.

RESULTS

An antifungal substance, 2-phenylethanol (PEA), was isolated from K. apiculata and demonstrated to have antimicrobial activity against selected phytopathogenic fungi. Experiments on P. italicum cells identified the mitochondria and the nucleus as particularly sensitive to inhibition. Regulation of P. italicum gene expression was investigated using RNA-Seq. PEA up-regulated genes involved with the peroxisome, regulation of autophagy, phosphatidylinositol signaling system, protein processing in endoplasmic reticulum, fatty acid metabolism, and inhibited ribosome, RNA polymerase, DNA replication, amino acid biosynthesis, aminoacyl-tRNA biosynthesis and cell cycle. Inhibitory responses revealed by RNA-Seq suggest that PEA might compete for attachment on the active site of phenylalanyl-tRNA synthetase (PheRS).

CONCLUSION

This study provided new insight on the mode of action of biocontrol yeast agents in controlling postharvest pathogenic fungi.