Membrane damage mechanism contributes to inhibition of trans-cinnamaldehyde on Penicillium italicum using Surface-Enhanced Raman Spectroscopy (SERS)

Dismantling of necrotroph Alternaria alternata by cellular intervention of Peppermint Oil Nanoemulsion (PNE)

Alternaria alternata, a common necrotrophic fungal pathogen, poses a significant threat to various crops, causing substantial yield losses and quality deterioration. In the present study, we explore the potential fungicidal properties of Peppermint Oil Nanoemulsion (PNE) against A. alternata and investigate its impact on the fungal phenotype. Our previous study synthesized the PNE using a nanoemulsion approach, optimizing its formulation for enhanced stability and efficacy. The present study extended the assessment of a multidisciplinary approach to comprehensively analyze the fungicidal efficacy of PNE against A. alternata. Notably, in a liquid growth medium, 0.5 % of PNE could reduce A. alternata's biomass by 96 %. PNE-treated mycelia were stained with a nitro-blue tetrazolium (NBT) dye to assess ROS accumulation during oxidative stress induced by PNE. A higher degree of ROS generative potential of PNE has appeared in 72 h treated mycelia. PNE-treated mycelium showed cell wall alterations, with red fluorescence peaking at 0.5 %, indicating a dose-dependent effect compared to the untreated control. Consequently, PNE treatment led to a significant early hour increase in electrical conductivity (EC), extended to 306.03-353.33 μS/cm compared to 277.67-280.33 μS/cm untreated control. Scanning Electron Microscopy (SEM) analysis of A. alternata reflects the osmotic imbalance and structural damage in mycelia as the obvious cause of fungal inhibition. In addition, a phenotype microarray analysis of PNE-treated A. alternata mycelia revealed a significant phenotypic loss in 37 out of 708 substrates, potentially impacting metabolic pathways essential for fungi's functional processes. The study found that downregulation of genes like Cre A, NmrA, SOD, IMP, EfP, and Erg, which are linked to A. alternata's stress coping mechanisms, leads to alterations in survival and adaptation. Additionally, understanding the phenotypic changes induced by PNE contributes to our knowledge of the mode of action of this nanoemulsion against A. alternata. In conclusion, this study provides a comprehensive analysis of the fungicidal and phenotypic effects of PNE, offering a promising avenue for sustainable fungal control. The implications of our research extend to the development of novel, natural fungicidal agents for agricultural applications.

The mechanistic insights of essential oil of Mentha piperita to control Botrytis cinerea and the prospection of lipid nanoparticles to its application

Botrytis cinerea is the phytopathogenic fungus responsible for the gray mold disease that affects crops worldwide. Essential oils (EOs) have emerged as a sustainable tool to reduce the adverse impact of synthetic fungicides. Nevertheless, the scarce information about the physiological mechanism action and the limitations to applying EOs has restricted its use. This study focused on elucidating the physiological action mechanisms and prospection of lipid nanoparticles to apply EO of Mentha piperita. The results showed that the EO of M. piperita at 500, 700, and 900 μL L-1 inhibited the mycelial growth at 100 %. The inhibition of spore germination of B. cinerea reached 31.43 % at 900 μL L-1. The EO of M. piperita decreased the dry weight and increased pH, electrical conductivity, and cellular material absorbing OD260 nm of cultures of B. cinerea. The fluorescence technique revealed that EO reduced hyphae width, mitochondrial activity, and viability, and increased ROS production. The formulation of EO of M. piperita loaded- solid lipid nanoparticles (SLN) at 500, 700, and 900 μL L-1 had particle size ∼ 200 nm, polydispersity index < 0.2, and stability. Also, the thermogravimetric analysis indicated that the EO of M. piperita-loaded SLN has great thermal stability at 50 °C. EO of M. piperita-loaded SLN reduced the mycelial growth of B. cinerea by 70 %, while SLN formulation (without EO) reached 42 % inhibition. These results supported that EO of M. piperita-loaded SLN is a sustainable tool for reducing the disease produced by B. cinerea.

Unveiling nutrient flow-mediated stress in plant roots using an on-chip phytofluidic device

The initial emergence of the primary root from a germinating seed is a pivotal phase that influences a plant's survival. Abiotic factors such as pH, nutrient availability, and soil composition significantly affect root morphology and architecture. Of particular interest is the impact of nutrient flow on thigmomorphogenesis, a response to mechanical stimulation in early root growth, which remains largely unexplored. This study explores the intricate factors influencing early root system development, with a focus on the cooperative correlation between nutrient uptake and its flow dynamics. Using a physiologically as well as ecologically relevant, portable, and cost-effective microfluidic system for the controlled fluid environments offering hydraulic conductivity comparable to that of the soil, this study analyzes the interplay between nutrient flow and root growth post-germination. Emphasizing the relationship between root growth and nitrogen uptake, the findings reveal that nutrient flow significantly influences early root morphology, leading to increased length and improved nutrient uptake, varying with the flow rate. The experimental findings are supported by mechanical and plant stress-related fluid flow-root interaction simulations and quantitative determination of nitrogen uptake using the total Kjeldahl nitrogen (TKN) method. The microfluidic approach offers novel insights into plant root dynamics under controlled flow conditions, filling a critical research gap. By providing a high-resolution platform, this study contributes to the understanding of how fluid-flow-assisted nutrient uptake and pressure affect root cell behavior, which, in turn, induces mechanical stress leading to thigmomorphogenesis. The findings hold implications for comprehending root responses to changing environmental conditions, paving the way for innovative agricultural and environmental management strategies.

Novel methods to monitor the biodegradation of polylactic acid (PLA) by Amycolatopsis orientalis and Amycolatopsis thailandensis

Plastics are essential in modern life, but their conventional production is problematic due to environmental pollution and waste management issues. Polylactic acid (PLA) is a widely used bioplastic that is bio-based and biodegradable, making it a key player in the bioeconomy. PLA has been proven to be degradable in various settings, including aqueous, soil, and compost environments. However, monitoring and optimizing PLA biodegradation remains challenging. This study proposes methods to improve the quantification of PLA biodegradation by Amycolatopsis spp. Ultrasound treatments (10 s) significantly improved the enumeration of viable Amycolatopsis cells by breaking the pellets into quantifiable individual cells. A separation technique combining ultrasound (120 s) and 40 μm cell strainers effectively isolated PLA particles from biomass to quantify PLA weight loss. This enabled the monitoring of PLA biofragmentation. Finally, CO2 production was measured according to ISO 14852 to quantify mineralization. Integrating these methods provides an improved quantification for PLA biodegradation along its different stages. In a case study, this led to the construction of a carbon balance where 85.1% of initial carbon content was successfully tracked. The developed techniques for monitoring of PLA biodegradation are essential to design future waste management strategies for biodegradable plastics.

Antifungal mechanism of Angelica sinensis essential oil against Penicillium roqueforti and its application in extending the shelf life of bread

There are a variety of reports on the application of Angelica sinensis essential oil (ASEO) in the biomedical field. However, the antifungal mechanism of ASEO has not been reported. In this study, the antifungal mechanism of ASEO against Penicillium roqueforti was investigated by proteomics and genomics. ASEO can increase the permeability of P. roqueforti cell membrane and decrease the content of lipid and trehalose. With the increase of glycerol content, the HOG signaling pathway can be upregulated. Consistent with the above phenotypic changes, proteomics confirmed that ASEO treatment inhibited the steroid synthesis pathway of P. roqueforti. The significant down-regulation of ERG4, ERG6, ERG25, SMT1, and FDFT1 gene expression confirmed this conclusion. Cluster+activates the MAPK and UPP signaling pathways and ultimately leads to cell apoptosis. The bread shelf life experiment showed that ASEO could extend the shelf life of bread up to day 7. This study provides new evidence for the antifungal activity of ASEO against P. roqueforti and will promote the use of ASEO in the preservation of food and agricultural products.

Antifungal activity of volatile and non-volatile metabolites of endophytes of Chloranthus elatior Sw

Agriculture crops that have fungal infections suffer significant economic losses and reduced crop output. Chemical fungicides are used to tackle the problem, although this has additional detrimental side effects. There is an urgent need for safe and novel antifungals. Volatiles from plant-beneficial endophytic fungi are considered promising alternatives for the biological control of fungal pathogens as a sustainable approach in an agroecosystem. In the present investigation, a volatile-emitting sterile endophytic fungus, Diaporthe sp. CEL3 with bio-fumigation activity, was isolated from leaves of the ethnomedicinal plant Chloranthus elatior Sw., collected from the Passighat forest of North-East India. The camphor odor volatiles of CEL3 showed an inhibitory effect against eight fungal pathogens in vitro and minimized the infections of Monilinia fructicola, a causal agent of cherry fruit rot, in VOC-exposed cherry fruits. Rhizoctonia solani, Botrytis cinerea, Pythium ultimum, and M. fructicola were maximally inhibited up to 51.5%, 55.8%, 61.9%, and 78.5%, respectively, in comparison to control by the volatiles. Another isolate, CEL7, identified as Curvularia sp., synthesized non-volatile, soluble antifungal metabolites in its cell-free extracts and exhibited antifungal action. Bioassay-guided fractionation revealed the presence of imidazole compounds- (2-aminoethyl)-1H-imidazole-2-carbaldehyde, Pyrazole 4, 5 imidazole, 1-formyl 3-ethyl, phenol compounds-Phenol, 4-[2-(methylamino) ethyl]-, 6-Nitro-3-chlorophenol, Phenol, 2,4,6-tri-tert-butyl-, etc., in the cell-free extracts, with a MIC value of 250-2,000 µg ml-1. Optimum VOC emission was achieved in a modified PDA medium with instantly smashed potato (150 g L-1), dextrose (20 g L-1), wheat husk (20 g L-1), and yeast extract (20 g L-1), with additional salts. Interestingly, endophytic CEL3 emitted different types of volatiles, and trans-verbenol (32.25%), geraniol (30.32%), trans-ocimenol (12.90%), and mentha-4,8-diene (5.16%) were the prime ones. These VOCs cause lethal leakage of protein and necessary intracellular molecules from the fungal pathogens. Thus, CEL3 could potentially be used as a bio-fumigating agent to control post-harvest infections caused by fungal pathogens. This study opens a new approach to the use of endophytic fungi in biocontrol.

Modes-of-action of antifungal compounds: Stressors and (target-site-specific) toxins, toxicants, or Toxin-stressors

Fungi and antifungal compounds are relevant to the United Nation's Sustainable Development Goals. However, the modes-of-action of antifungals-whether they are naturally occurring substances or anthropogenic fungicides-are often unknown or are misallocated in terms of their mechanistic category. Here, we consider the most effective approaches to identifying whether antifungal substances are cellular stressors, toxins/toxicants (that are target-site-specific), or have a hybrid mode-of-action as Toxin-stressors (that induce cellular stress yet are target-site-specific). This newly described 'toxin-stressor' category includes some photosensitisers that target the cell membrane and, once activated by light or ultraviolet radiation, cause oxidative damage. We provide a glossary of terms and a diagrammatic representation of diverse types of stressors, toxic substances, and Toxin-stressors, a classification that is pertinent to inhibitory substances not only for fungi but for all types of cellular life. A decision-tree approach can also be used to help differentiate toxic substances from cellular stressors (Curr Opin Biotechnol 2015 33: 228-259). For compounds that target specific sites in the cell, we evaluate the relative merits of using metabolite analyses, chemical genetics, chemoproteomics, transcriptomics, and the target-based drug-discovery approach (based on that used in pharmaceutical research), focusing on both ascomycete models and the less-studied basidiomycete fungi. Chemical genetic methods to elucidate modes-of-action currently have limited application for fungi where molecular tools are not yet available; we discuss ways to circumvent this bottleneck. We also discuss ecologically commonplace scenarios in which multiple substances act to limit the functionality of the fungal cell and a number of as-yet-unresolved questions about the modes-of-action of antifungal compounds pertaining to the Sustainable Development Goals.

Exploring dynamic changes of fungal cellular components during nanoemulsion treatment by multivariate microRaman imaging

Recently, essential oils (EO) have gained a lot of interest for use as antifungal agent in food and agricultural industry and extensive research is ongoing to understand their mode of action. However, the exact mechanism is not yet elucidated. Here, we integrated spectral unmixing and Raman microspectroscopy imaging to unveil the antifungal mechanism of green tea EO based nanoemulsion (NE) against Magnaporthe oryzae. The dramatic change in protein, lipid, adenine, and guanine bands indicate that NE has a significant impact on the protein, lipid and metabolic processes of purine. The results also demonstrated that the NE treatment caused damage to fungal hyphae by inducing a physical injury leading to cell wall damage and loss of integrity. Our study shows that MCR-ALS (Multivariate Curve Resolution-Alternating Least Squares) and N-FINDR (N-finder algorithm) Raman imaging could serve as a suitable complementary package to the traditional methods, for revealing the antifungal mechanism of action of EO/NE.

Selected Simple Natural Antimicrobial Terpenoids as Additives to Control Biodegradation of Polyhydroxy Butyrate

In this experimental research, different types of essential oils (EOs) were blended with polyhydroxybutyrate (PHB) to study the influence of these additives on PHB degradation. The blends were developed by incorporating three terpenoids at two concentrations (1 and 3%). The mineralization rate obtained from CO2 released from each sample was the factor that defined biodegradation. Furthermore, scanning electron microscope (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) were used in this research. The biodegradation percentages of PHB blended with 3% of eucalyptol, limonene, and thymol after 226 days were reached 66.4%, 73.3%, and 76.9%, respectively, while the rate for pure PHB was 100% after 198 days, and SEM images proved these results. Mechanical analysis of the samples showed that eucalyptol had the highest resistance level, even before the burial test. The other additives showed excellent mechanical properties although they had less mechanical strength than pure PHB after extrusion. The samples' mechanical properties improved due to their crystallinity and decreased glass transition temperature (Tg). DSC results showed that blending terpenoids caused a reduction in Tg, which is evident in the DMA results, and a negligible reduction in melting point (Tm).

Preparation of Citral Compound and Its Bamboo Antimildew Properties

To reduce the amount of citral used without reducing the antimildew performance of bamboo, the citral compound preparation process, the distribution of the compound in bamboo, and its antimildew performance were investigated using the Oxford cup method, Fourier-transform infrared spectroscopy, and ultraviolet spectrophotometry. The results revealed that the combination of citral with cinnamaldehyde or thymol may lead to partial chemical reactions, which may change the chemical structure of citral and affect its bacteriostatic properties. The bacteriostatic properties of the citraldehyde thymol compound against common molds of bamboo were considerably superior to those of the citral cinnamaldehyde compound. The limonaldehyde thymol compound showed a low distribution trend outside and vice versa inside in the treated bamboo. The citral thymol compound exhibited good antimildew performance at a concentration of 200 mg/mL. The citral thymol compound could reduce the amount of citral by approximately 67 mg/mL without reducing the antimildew performance of bamboo.

The plasma membrane H+-ATPase is critical for cell growth and pathogenicity in Penicillium digitatum

The plasma membrane H⁺-ATPase (PMA1) is a major cytosolic pH regulator and a potential candidate for antifungal drug discovery due to its fungal specificity and criticality. In this study, the function of Penicillum digitatum PMA1 was characterized through RNA interference (RNAi) and overexpression technology. The results showed that silencing the PMA1 gene reduces cell growth and pathogenicity, and increases susceptibility of P. digitatum to proton pump inhibitors (PPIs). Under scanning electron microscopy (SEM) and transmission electron microscopy (TEM) examination, cell morphology was significantly altered in the PMA1- silenced mutant (si57). When compared with wild type (WT) and the overexpressed mutant (oe9), the cell walls of the si57 mutant were thicker and their cell membrane damage manifested particularly at sites of polarized growth. Consistent with the morphological change on the cell wall, chitin and glucan content of the cell wall of si57 were significantly lower and accompanied with increased activities of chitinase and glucanase. The lower ergosterol content in the si57 mutant then increased cell membrane permeability, ultimately leading to leakage of cytoplasmic contents such as ions, reduced sugars and soluble proteins. Furthermore, significantly decreased activity of cell wall degrading enzymes of si57 during citrus fruit infections indicates a reduced pathogenicity in this mutant. We conclude that PMA1 in P. digitatum plays an important role in maintaining pathogenesis and PMA1 could be a candidate novel fungicidal drug discovery for citrus green mold. KEY POINTS: Silencing PMA1 gene decreased the growth and pathogenicity of P. digitatum. Silencing PMA1 gene damaged cell wall and cell membrane integrity of P. digitatum. PMA1 appears to be a suitable fungicidal target against citrus green mold.

Identification of Volatile Organic Compounds Produced by Xenorhabdus indica Strain AB and Investigation of Their Antifungal Activities

Xenorhabdus spp. are symbiotic bacteria associated with entomopathogenic nematodes to form a model complex that is used for the biological control of insect pests. These bacteria also produce secondary metabolites that have commercial potential in the pharmaceutical and agroforestry industries. Volatile organic compounds (VOCs) produced by the Xenorhabdus indica "strain AB" have been shown to have significant antifungal activity against Fusarium oxysporum f. sp. cucumerinum. Using gas chromatography-mass spectrometry, we identified 61 volatiles in the mixture of VOCs emitted by strain AB compared to a control strain, 6 of which were investigated for their antifungal activities. Of these, methyl anthranilate exhibited the highest mycelial growth suppression toward F. oxysporum, with a minimum inhibitory volume (MIV) of 50 μL/plate. Fluorescence assays, scanning electron microscopy, and measurements of the leakage of intracellular components revealed that the use of methyl anthranilate changed cell wall and cell membrane integrity as well as the permeability of the plasma membrane. Furthermore, methyl anthranilate treatment upregulated the transcription level of target genes related to redox reactions and the cell wall integrity pathway. The results suggest a novel mechanism used by Xenorhabdus spp. to overcome competitors during its life cycle and open up a new approach to using these bacteria in biological control. IMPORTANCE Fungal phytopathogens, particularly Fusarium oxysporum, are a major problem worldwide, especially in the postharvest of vital economic crops. Concerns about negative effects on the environment and human health have led to increasing restrictions on the use of chemical fungicides, and therefore, biological control agents are now being considered alternatives. It is in this context that we investigated the antifungal activity of VOCs produced by X. indica strain AB against F. oxysporum. We found that AB VOCs have a strong effect on the growth of the fungal phytopathogen. In addition, 85% of the identified volatile compounds were determined to be new compounds, opening up new lines of research to discover their properties, effects, and potential for pharmaceutical and agricultural applications. Antifungal assays proved that four of the six compounds with a high concentration in the GC-MS profile had a significant inhibitory effect on pathogen growth. Accordingly, this study opens up a new approach for the use of these bacteria in biocontrol.

Encephalartos villosus Lem. Displays a Strong In Vivo and In Vitro Antifungal Potential against Candida glabrata Clinical Isolates

Recently, Candida glabrata has been recognized as one of the most common fungal species that is highly associated with invasive candidiasis. Its spread could be attributed to its increasing resistance to antifungal drugs. Thus, there is a high need for safer and more efficient therapeutic alternatives such as plant extracts. Here, we investigated the antifungal potential of Encephalartos villosus leaves methanol extract (EVME) against C. glabrata clinical isolates. Tentative phytochemical identification of 51 metabolites was conducted in EVME using LC–MS/MS. EVME demonstrated antifungal activity with minimum inhibitory concentrations that ranged from 32 to 256 µg/mL. The mechanism of the antifungal action was studied by investigating the impact of EVME on nucleotide leakage. Additionally, a sorbitol bioassay was performed, and we found that EVME affected the fungal cell wall. In addition, the effect of EVME was elucidated on the efflux activity of C. glabrata isolates using acridine orange assay and quantitative real-time PCR. EVME resulted in downregulation of the expression of the efflux pump genes CDR1, CDR2, and ERG11 in the tested isolates with percentages of 33.33%, 41.67%, and 33.33%, respectively. Moreover, we investigated the in vivo antifungal activity of EVME using a murine model with systemic infection. The fungal burden was determined in the kidney tissues. Histological and immunohistochemical studies were carried out to investigate the effect of EVME. We noticed that EVME reduced the congestion of the glomeruli and tubules of the kidney tissues of the rats infected with C. glabrata. Furthermore, it decreased both the proinflammatory cytokine tumor necrosis factor-alpha and the abnormal collagen fibers. Our results reveal, for the first time, the potential in vitro (by inhibition of the efflux activity) and in vivo (by decreasing the congestion and inflammation of the kidney tissues) antifungal activity of EVME against C. glabrata isolates.

Antifungal Activity of Polymethoxylated Flavonoids (PMFs)-Loaded Citral Nanoemulsion against Penicillium italicum by Causing Cell Membrane Damage

A major citrus postharvest pathogen, Penicillium italicum (P. italicum), causes substantial economic losses in citrus. In this study, a citral nanoemulsion containing polymethoxylated flavonoids (PMFs), the antimicrobial compounds from citrus, was prepared. The antifungal activity and potential antifungal mechanisms of the nanoemulsion against P. italicum were evaluated. The results showed that the growth of P. italicum was effectively inhibited by the nanoemulsion, with a minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of 62.5 and 250 mg L−1, respectively. The nanoemulsion significantly inhibited spore germination and mycelial growth, and it altered the morphology of P. italicum. In addition, the permeability of the cell membrane increased with increasing nanoemulsion concentrations, as evidenced by a rapid rise in extracellular electric conductivity and stronger red fluorescence from mycelia (propidium iodide staining). Compared with the control, the nanoemulsion treatment induced a decrease in total lipid and ergosterol contents in P. italicum cells by 64.61% and 60.58%, respectively, demonstrating that membrane integrity had been disrupted. The results indicated that the PMFs-loaded nanoemulsion exerted antifungal activity against P. italicum by disrupting cell membrane integrity and permeability; such a nanoemulsion may be used as a potential fungicide substitute for preservation in citrus fruits.

Effect of plant-derived antimicrobials against multidrug-resistant Salmonella Heidelberg in ground Turkey

Salmonella Heidelberg (SH) is a highly invasive human pathogen for which turkeys can serve as reservoir hosts. Colonization of turkeys with SH may result in potential contamination and is a greater challenge to prevent in comminuted products. Antimicrobial efficacy of 3 GRAS-status plant-derived antimicrobials (PDAs), lemongrass essential oil (LG), citral (CIT), and trans-cinnamaldehyde (TC), against SH in ground turkey, a comminuted product implicated in several outbreaks, was evaluated in this study. Ground turkey samples inoculated with ∼3.50 log10 CFU/g of a three-strain SH cocktail were treated with either LG, CIT, or TC at either 0.5, 1, or 2% (vol/wt). Samples were stored at 4°C, and bacterial enumeration was performed on d 0, 1, 3, and 5. Appropriate controls were included alongside all treatments. Fluorescence microscopy was performed to evaluate the direct impact of the PDAs against SH in vitro. Appearance and aroma difference testing of raw patties was also performed for select treatments with trained sensory panelists. Treatment with 2% TC yielded a 2.5 log10 CFU/g reduction by d 1 and complete reduction by d 5 (P < 0.05). By d 3, 2% CIT and 2% LG resulted in SH reduction of at least 1.7 log10 CFU/g (P < 0.05). Addition of 1% TC resulted in reduction of at least 1.8 log10 CFU/g by d 3 (P < 0.05). Participants could distinguish PDA-treated raw patties by aroma. Most participants (7/11) could not distinguish patties treated with 0.5% TC based on appearance. Microscopic images indicate that all PDAs resulted in disruption of the SH membrane. Results of the present study indicate that the three tested PDAs, LG, CIT, and TC are effective against SH in ground turkey, indicating their potential use as interventions to mitigate Salmonella contamination in comminuted turkey products.

Combined transcriptome and metabolome analyses reveal the potential mechanism for the inhibition of Penicillium digitatum by X33 antimicrobial oligopeptide

Penicillium digitatum is the primary spoilage fungus that causes green mold during postharvest in citrus. To reduce economic losses, developing more efficient and less toxic natural antimicrobial agents is urgently required. We previously found that the X33 antimicrobial oligopeptide (X33 AMOP), produced by Streptomyces lavendulae X33, exhibited a sterilization effect on P. digitatum. In this study, the effects, and physiological mechanisms of X33 AMOP as an inhibitor of P. digitatum were investigated. The transcriptional and metabolome profiling of P. digitatum exposed to X33 AMOP revealed 3648 genes and 190 metabolites that were prominently changed. The omics analyses suggested that X33 AMOP mainly inhibited P. digitatum growth by affecting cell integrity, genetic information delivery, oxidative stress tolerance, and energy metabolism. These findings provide helpful information regarding the antimicrobial mechanism of X33 AMOP against P. digitatum at the molecular level and indicate that X33 AMOP is a potential candidate to control P. digitatum.

Active compound identification by screening 33 essential oil monomers against Botryosphaeria dothidea from postharvest kiwifruit and its potential action mode

The antifungal activity of postharvest kiwifruit against the pathogen Botryosphaeria dothidea was evaluated for 33 essential oil monomers. The possible mechanism for the known active compounds were further assessed in this study. The results show all the EO components exhibit inhibitory effects on the pathogen to different degrees except for Farnesol. Carbon chain length and C₂-C₃ double bonds had a great effect on the antifungal activities of aldehydes. Of all of these, carvacrol had the strongest antifungal activity with EC₅₀ of 12.58 μL/L and EC₉₀ of 22.08 μL/L. Carvacrol also exhibits significant inhibitory effects on the pathogen, both in vivo and in vitro. Carvacrol evidently alters the hyphal morphology of B. dothidea and severely damages cell membrane and inhibits the formation of lipid components on the membrane. As cell membrane permeability increases, intracellular homeostasis including ion and biomacromolecules were destroyed by carvacrol. Furthermore, carvacrol appears to significantly inhibit mitochondrial activity and respiration rates, resulting in cell death of B. dothidea. Our results provide evidence that carvacrol could be a very useful compound for controlling postharvest rot soft in kiwifruit.

Antimycotic Effects of 11 Essential Oil Components and Their Combinations on 13 Food Spoilage Yeasts and Molds

Food safety is important to reduce food spoilage microorganisms and foodborne pathogens. However, food safety is challenging, as customers' demand for natural preservatives is increasing. Essential oils (EOs) and their components (EOCs) are alternative antibacterial and antimycotic food additives. In this study, the minimal inhibitory concentrations (MIC) of 11 different EOCs against 13 food spoilage molds and yeasts were investigated via the microdilution method. Cinnamaldehyde (CA) revealed the lowest MIC for all tested strains and all EOCs (32.81-328.1 µg ml-1). However, CA is organoleptic and was therefore combined with other EOCs via the checkerboard method. Overall, 27 out of 91 combinations showed a synergistic effect, and both respective EOC concentrations could be reduced by maintaining MIC. Thereby, the combination with citral or citronellal showed promising results. The concentration-dependent effect of CA was studied in further detail on Saccharomyces cerevisiae, with CA causing delayed growth-kinetics and reduced total cell numbers. In addition, flow cytometric measurements combined with live-dead staining indicate the fungicidal effect of CA, due to decreasing total cell numbers and increasing relative amount of propidium iodide-positive cells. In this study, we demonstrated that CA is a potent candidate for the use as a natural preservative against food-relevant mold and yeasts showing fungistatic and fungicidal effects. Therefore, CA and EOC combinations with respective lower EOC concentrations reduce organoleptic reservations, which ease their application in the food industry.

A SERS-LFA biosensor combined with aptamer recognition for simultaneous detection of thrombin and PDGF-BB in prostate cancer plasma

An innovative surface-enhanced Raman spectroscopy and lateral flow assay (SERS-LFA) biosensor combined with aptamer recognition had been developed for the convenient, rapid, sensitive and accurate detection of thrombin and platelet-derived growth factor-BB (PDGF-BB) associated with prostate cancer simultaneously. During the biosensor operation, thrombin and PDGF-BB in the sample were recognized and combined by thiol-modified aptamers immobilized on Au-Ag hollow nanoparticles (Au-Ag HNPs) surface and biotinylated aptamers immobilized on the test lines of the biosensor. Thus, thrombin and PDGF-BB were simultaneously captured between detection aptamers and capture aptamers in a sandwich structure. Finite difference time domain simulation confirmed that 'hot spots' appeared at the gaps of Au-Ag HNPs dimer in the enhanced electromagnetic field compared to that of a single Au-Ag HNP, indicating that the aggregated Au-Ag HNPs owned a good SERS signal amplification effect. The detection limits of thrombin and PDGF-BB in human plasma were as low as 4.837 pg ml^-1and 3.802 pg ml^-1, respectively. Moreover, the accuracy of the biosensor which was applied to detect thrombin and PDGF-BB in prostate cancer plasma had been verified. This designed biosensor had broad application prospects in the clinical diagnosis of prostate cancer.

Cinnamaldehyde inhibits the growth of Phytophthora capsici through disturbing metabolic homoeostasis

Background

Phytophthora capsici Leonian (P. capsici) can cause wilting and roots rotting on pepper and other cash crops. The new fungicide cinnamaldehyde (CA) has high activity against this pathogen. However, its potential mechanism is still unknown.

Methods

In order to gain insights into the mechanism, isobaric tags for relative and absolute quantification (iTRAQ)-based quantitative proteomics was used to analyze P. capsici treated with CA. The iTRAQ results were evaluated by parallel reaction monitoring (PRM) analysis and quantitative real-time PCR (qRT-PCR) analysis. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis was used to speculate the biochemical pathways that the agent may act on.

Results

The results showed that 1502 differentially expressed proteins were identified, annotated and classified into 209 different terms (like metabolic process, cellular process, single-organism process) based on Gene Ontology (GO) functional enrichment analysis and nine different pathways (glyoxylate and dicarboxylate metabolism, fatty acid metabolism and so on) based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. This study suggested that CA disordered fatty acid metabolism, polysaccharide metabolism and leucine metabolism. Based on PRM analysis, five proteins including CAMK/CAMK1 protein kinase, glucan 1,3-beta-glucosidase, 1,3-beta-glucanosyltransferase, methylcrotonoyl-CoA carboxylase subunit alpha and isovaleryl-CoA dehydrogenase were down-regulated in P. capsici treated with CA. Furthermore, the qRT-PCR analysis showed that the gene expression level of the interested proteins was consistent with the protein expression level, except for CAMK/CAMK1 protein kinase, acetyl-CoA carboxylase and fatty acid synthase subunit alpha.

Conclusions

CA destroyed the metabolic homoeostasisof P. capsici, which led to cell death. This is the first proteomic analysis of P. capsici treated with CA, which may provide an important information for exploring the mechanism of the fungicide CA against P. capsici.

Non-target bioanalytical eight-dimensional hyphenation including bioassay, heart-cut trapping, online desalting, orthogonal separations and mass spectrometry

It is still a challenge to discover and identify individual bioactive compounds directly in multicomponent mixtures. Current workflows are too tedious for routine use. Hence, the hyphenation of separation and detection techniques is a powerful tool to maximize the information obtained by a single sample run. A robust eight-dimensional (8D) hyphenation was developed. Orthogonal separations, biological assay detection, analyte trapping, desalting, and physico-chemical detections were arranged in the following order, i.e. 1) normal phase high-performance thin-layer chromatography (NP-HPTLC) separation, 2) Vis detection, 3) UV detection, 4) fluorescence detection (FLD), 5) bioassay for effect-directed analysis (EDA), 6) heart-cut trapping/desalting/elution to reversed phase high-performance liquid chromatography (RP-HPLC) separation, 7) photodiode array (PDA) and 8) mass spectrometry (MS) detection. For the first time, the hyphenation exploited online analyte trapping to desalt the eluted bioactive zone from the plate containing highly salted bioassay media. Subsequent valve switching guided the trapped analyte(s) to the main column, followed by multiple detection. As proof-of-principle, cinnamon samples were analyzed by NP-HPTLC-UV/Vis/FLD-EDA-RP-HPLC-PDA-MS, whereby a bioactive zone was separated into two distinct peaks detected by PDA and MS to be 2-methoxy cinnamaldehyde and cinnamaldehyde. The developed 8D hyphenation is applicable for routine, allowing the non-target high-throughput screening of complex samples for individual bioactive compounds.

Anti-bacterial and wound healing-promoting effects of zinc ferrite nanoparticles

BACKGROUND

Increasing antibiotic resistance continues to focus on research into the discovery of novel antimicrobial agents. Due to its antimicrobial and wound healing-promoting activity, metal nanoparticles have attracted attention for dermatological applications. This study is designed to investigate the scope and bactericidal potential of zinc ferrite nanoparticles (ZnFe₂O₄ NPs), and the mechanism of anti-bacterial action along with cytocompatibility, hemocompatibility, and wound healing properties.

RESULTS

ZnFe₂O₄ NPs were synthesized via a modified co-precipitation method. Structure, size, morphology, and elemental compositions of ZnFe₂O₄ NPs were analyzed using X-ray diffraction pattern, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. In PrestoBlue and live/dead assays, ZnFe₂O₄ NPs exhibited dose-dependent cytotoxic effects on human dermal fibroblasts. In addition, the hemocompatibility assay revealed that the NPs do not significantly rupture red blood cells up to a dose of 1000 µg/mL. Bacterial live/dead imaging and zone of inhibition analysis demonstrated that ZnFe₂O₄ NPs showed dose-dependent bactericidal activities in various strains of Gram-negative and Gram-positive bacteria. Interestingly, NPs showed antimicrobial activity through multiple mechanisms, such as cell membrane damage, protein leakage, and reactive oxygen species generation, and were more effective against gram-positive bacteria. Furthermore, in vitro scratch assay revealed that ZnFe₂O₄ NPs improved cell migration and proliferation of cells, with noticeable shrinkage of the artificial wound model.

CONCLUSIONS

This study indicated that ZnFe₂O₄ NPs have the potential to be used as a future antimicrobial and wound healing drug.

A review of the methods used to determine the target site or the mechanism of action of essential oils and their components against fungi

Essential oils (EOs) are complex mixtures of compounds derived from plants that exhibit antimicrobial activity. Several studies have demonstrated their antifungal activity in food matrices or in vitro via vapor phase or direct addition. Recently, researchers are focusing on elucidating the target site or the mechanism of action of various EOs. Past research has suggested evidence of how EOs act in the fungal cells via assays assessed from cell wall alterations or gene expression modifications. However, no previous reports have summarized most methods for finding the target site of the mechanism of action for EOs. Therefore, this review presents the methods and assays used to discover the target site or the mechanism of action of EOs against fungal cells. Researchers commonly analyze the plasma membrane integrity using various techniques as well as the changes in cell morphology. Meanwhile, the quantification of the activity of the mitochondrial enzymes, ROS species, and gene expression are less assayed.

Development of bactericidal spinel ferrite nanoparticles with effective biocompatibility for potential wound healing applications

The current study was devised to explore the antibacterial activity and underlying mechanism of spinel ferrite nanoparticles (NPs) along with their biocompatibility and wound healing potentials. In this regard, nickel ferrite and zinc/nickel ferrite NPs were synthesized via a modified co-precipitation method and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy Energy-dispersive X-ray spectroscopy (EDX). The biocompatibility of the synthesized NPs with human dermal fibroblast (HDF) and red blood cells (RBCs) was assessed. The biocompatible concentrations of the NPs were used to investigate the antimicrobial activity against various pathogenic Gram-negative and Gram-positive bacteria. The mode of bactericidal action was also explored. In vitro scratch assay was performed to evaluate the wound healing potential of NPs. The SEM-EDX analysis showed that the average particles size of nickel ferrite and zinc/nickel ferrite were 49 and 46 nm, respectively, with appropriate elemental composition and homogenous distribution. The XRD pattern showed all the characteristic diffraction peaks of spinel ferrite NPs, which confirmed the synthesis of the pure phase cubic spinel structure. The biocompatible concentration of nickel ferrite and zinc/nickel ferrite NPs was found to be 250 and 125 μg ml-1, respectively. Both the NPs showed inhibition against all the selected strains in the concentration range of 50 to 1000 μg ml-1. Studies on the underlying antimicrobial mechanism revealed damage to the cell membrane, protein leakage, and intracellular reactive oxygen species production. The in vitro scratch assay confirmed the migration and proliferation of fibroblast with artificial wound shrinkage. This study shows that nickel ferrite and zinc/nickel ferrite NPs could be a strong candidate for antibacterial and wound healing nano-drugs.

The Antifungal Activity of Loquat (Eriobotrya japonica Lindl.) Leaves Extract Against Penicillium digitatum

This study was performed to determine the antifungal activity of loquat (Eriobotrya japonica Lindl) leaf extract (LLE) against the citrus postharvest pathogen Penicillium digitatum (P. digitatum). The LLE exhibited an antifungal activity against P. digitatum, with a minimum inhibitory concentration (MIC) of 0.625 mg/ml and a minimum fungicidal concentration (MFC) of 1.25 mg/ml. Significant inhibitory effects of LLE on mycelial growth and spore germination of P. digitatum were seen in a dose-dependent manner. Simultaneously, to investigate possible antifungal mechanisms by LLE, we analyzed their influence on morphological changes, cell membrane permeability, cell wall and cell membrane integrity, and adenosine phosphates (ATP, ADP, and AMP) levels. Alterations, such as sunken surface and malformation, occurred in the LLE-treated P. digitatum spores. Furthermore, intracellular inclusion content decreased after LLE treatment, indicating an increase in cell membrane permeability. Besides, the LLE treatment induced a significant decline in the level of adenosine monophosphate (AMP), adenosine diphosphate (ADP), and adenosine triphosphate (ATP) with a noticeable addition of extracellular ATP, ADP, and AMP during the entire treatment period. Overall, the results manifested that the antifungal activity of LLE against P. digitatum can be attributed to the derangement of cell membrane permeability and disordered energy metabolism. This is the first report on the mechanism of antifungal activity of LLE and could be useful in the development of targeted fungicides from natural origin.

4-Ethylphenol, A Volatile Organic Compound Produced by Disease-Resistant Soybean, Is a Potential Botanical Agrochemical Against Oomycetes

Oomycetes, represented by Phytophthora, are seriously harmful to agricultural production, resulting in a decline in grain quality and agricultural products and causing great economic losses. Integrated management of oomycete diseases is becoming more challenging, and plant derivatives represent effective alternatives to synthetic chemicals as novel crop protection solutions. Biologically active secondary metabolites are rapidly synthesized and released by plants in response to biotic stress caused by herbivores or insects, as well as pathogens. In this study, we identified groups of volatile organic compounds (VOCs) from soybean plants inoculated with Phytophthora sojae, the causal agent of soybean root rot. 4-Ethylphenol was present among the identified VOCs and was induced in the incompatible interaction between the plants and the pathogen. 4-Ethylphenol inhibited the growth of P. sojae and Phytophthora nicotianae and had toxicity to sporangia formation and zoospore germination by destroying the pathogen cell membrane; it had a good control effect on soybean root rot and tobacco black shank in the safe concentration range. Furthermore, 4-Ethylphenol had a potent antifungal activity against three soil-borne phytopathogenic fungi, Rhizoctonia solani, Fusarium graminearum, and Gaeumannomyces graminis var tritici, and four forma specialis of Fusarium oxysporum, which suggest a potential to be an eco-friendly biological control agent.

Inhibitory Activity of Essential Oils against Vibrio campbellii and Vibrio parahaemolyticus

Vibriosis, caused by Vibrio strains, is an important bacterial disease and capable of causing significant high mortality in aquatic animals. Essential oils (EOs) have been considered as an alternative approach for the treatment of aquatic bacterial diseases. In this study, we evaluated the antibacterial activity of essential oils (n = 22) or essential oil components (EOCs, n = 12) against Vibrio strains belonging to the harveyi clade. It was verified by three different approaches, e.g., (i) a bacterial growth assay, comparing Vibrio growth with or without EO(C)s at various concentrations; (ii) a vapor-phase-mediated susceptibility assay, comparing the effect of EO(C)s on bacterial growth through the vapor phase; and (iii) a quorum sensing-inhibitory assay, based on specific inhibition of quorum sensing-regulated bioluminescence. The results showed that, in the bacterial growth assay, EOs of Melaleuca alternifolia and Litsea citrata at 0.0001%, Eucalyptus citriodora at 0.01% can inhibit the growth of Vibrio campbellii BB120. These EOs can also prevent the growth of V. parahaemolyticus strains but need to be present at a higher concentration (0.1%). Moreover, in the vapor-phase-mediated susceptibility assay, EOs of M. alternifolia, L. citrata and E. citriodora can inhibit the growth of V. campbellii BB120 through their vapor phase. However, V. parahaemolyticus strains (CAIM170, LMG2850 and MO904) cannot be inhibited by these EOs. Additionally, in the quorum sensing-inhibitory assay, EOs of Mentha pulegium, Cuminum cyminum, Zingiber officinalis, and E. citriodora, all at 0.001%, have quorum sensing-inhibitory activity in V. campbellii BB120. Taken together, our study provides substantial evidence that usage of the major components, individually or in combination, of the tested commercial EOs (extracted from M. alternifolia, L. citrata, and E. citriodora) could be a promising approach to control V. campbellii BB120.

Physiological and Proteomic Analysis of Penicillium digitatum in Response to X33 Antifungal Extract Treatment

Penicillium digitatum is a widespread pathogen among Rutaceae species that causes severe fruit decay symptoms on infected citrus fruit (known as citrus green mold). The employment of fungicides can effectively control the citrus green mold, significantly reducing agricultural economic loss. In this study, we found that the X33 antifungal extract produced by Streptomyces lavendulae strain X33 inhibited the hyphae polarization of P. digitatum. Additionally, physiological and proteomic analysis strategies were applied to explore the inhibitory mechanism of the X33 antifungal extract of the S. lavendulae strain X33 on the mycelial growth of P. digitatum. A total of 277 differentially expressed proteins, consisting of 207 upregulated and 70 downregulated, were identified from the comparative proteomics analysis. The results indicated that the X33 antifungal extract induced mitochondrial membrane dysfunction and cellular integrity impairment, which can affect energy metabolism, oxidative stress, and transmembrane transport. The improved alkaline phosphatase activity and extracellular conductivity, increased H₂O₂ and malondialdehyde contents, and inhibition of energy, amino acid, and sugar metabolism indicated that the oxidative stress of P. digitatum is induced by the X33 antifungal extract. These findings provided insight into the antifungal mechanism of the X33 antifungal extract against P. digitatum by suggesting that it may be an effective fungicide for controlling citrus postharvest green mold.

A flavonone pinocembroside inhibits Penicillium italicum growth and blue mold development in 'Newhall' navel oranges by targeting membrane damage mechanism

Blue mold caused by Penicillium italicum is an important postharvest disease of citrus fruit. The antifungal activity of a flavonone pinocembroside compound obtained from the fruit of Ficus hirta Vahl., was evaluated against P. italicum. Pinocembroside showed antifungal activity against in vitro mycelial growth of P. italicum, with the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of 200 and 800 mg/L, respectively. The blue mold development on 'Newhall' navel oranges was inhibited by pinocembroside in a dose-dependent manner. Moreover, pinocembroside might exert its antifungal activity via membrane-targeted mechanism with increasing membrane permeability, reduction of antioxidant enzyme activity and acceleration of lipid peroxidation in the pathogen. This pioneering study suggested that pinocembroside suppressed postharvest blue mold by direct inhibition of P. italicum mycelial growth via membrane-targeting mechanism, thus providing a novel mode of action against traditional fungicides for controlling blue mold of citrus fruit.

Pinocembrin-7-Glucoside (P7G) Reduced Postharvest Blue Mold of Navel Orange by Suppressing Penicillium italicum Growth

The current study aimed to examine the in vitro and in vivo antifungal potential of pinocembrin-7-glucoside (P7G). P7G is an antifungal flavanone glycoside isolated from Ficus hirta Vahl. fruit against Penicillium italicum, a causative pathogen of blue mold disease in citrus fruit, and this study elucidates its possible action mechanism. P7G had a prominent mycelial growth inhibitory activity against P. italicum, with an observed half maximal effective concentration, minimum inhibitory concentration and minimum fungicidal concentration of 0.08, 0.2, and 0.8 g/L, respectively. The data from the in vivo test show that P7G significantly reduced blue mold symptoms and disease development of P. italicum in artificially inoculated "Newhall" navel orange. Compared to the control, increases in the cell membrane permeability of P. italicum supernatant and decreases in the intracellular constituent (e.g., soluble protein, reducing sugar, and total lipid) contents of P. italicum mycelia were identified, supporting scanning electron microscopy and transmission electron microscopy observations. Furthermore, a marked decline in both chitin and glucanase contents of P. italicum mycelia treated with P7G was induced by increasing its related degrading enzyme activities, suggesting that the cell wall structure was destroyed. The current study indicated that P7G may be a novel alternative for reducing blue mold by suppressing mycelial growth of P. italicum via a cell membrane/wall-targeting mechanism.

Synergistic inhibition effect of citral and eugenol against Aspergillus niger and their application in bread preservation

Consumers' preferences for cleaner label products require the food industry to replace synthetic preservatives with natural substitutes. Therefore, the synergistic inhibitory effect of eugenol and citral (S_EC) on Aspergillus niger was explored. On this basis, the antimicrobial sachet containing S_EC was developed and its application potential in bread preservation was evaluated. The content of reactive oxygen species (ROS) and malondialdehyde (MDA) showed that S_EC could significantly induce lipid peroxidation in cell membranes, in which citral played a leading role. The permeation experiments of SEM, TEM, propyl iodide and fluorescein diacetate showed that S_EC could destroy the integrity of the cell membrane. Eugenol contributed more than citral. The OD₂₆₀ and the relative conductivity of the S_EC group increased by 5.2 and 4.1 times, respectively, after 8 h. Finally, the shelf life experiment of bread showed that the antimicrobial sachets containing S_EC could significantly prolong the shelf life of bread without producing unpleasant odour.

Insights into the Relationships Between Herbicide Activities, Molecular Structure and Membrane Interaction of Cinnamon and Citronella Essential Oils Components

Since the 50's, the massive and "environmental naïve" use of synthetic chemistry has revolutionized the farming community facing the dramatic growth of demography. However, nowadays, the controversy grows regarding the long-term harmful effects of these products on human health and the environment. In this context, the use of essential oils (EOs) could be an alternative to chemical products and a better understanding of their mode of biological action for new and optimal applications is of importance. Indeed, if the biocidal effects of some EOs or their components have been at least partly elucidated at the molecular level, very little is currently known regarding their mechanism of action as herbicides at the molecular level. Here, we showed that cinnamon and Java citronella essential oils and some of their main components, i.e.,, cinnamaldehyde (CIN), citronellal (CitA), and citronellol (CitO) could act as efficient herbicides when spread on A. thaliana leaves. The individual EO molecules are small amphiphiles, allowing for them to cross the mesh of cell wall and directly interact with the plant plasma membrane (PPM), which is one of the potential cellular targets of EOs. Hence, we investigated and characterized their interaction with biomimetic PPM while using an integrative biophysical approach. If CitO and CitA, maintaining a similar chemical structure, are able to interact with the model membranes without permeabilizing effect, CIN belonging to the phenylpropanoid family, is not. We suggested that different mechanisms of action for the two types of molecules can occur: while the monoterpenes could disturb the lipid organization and/or domain formation, the phenylpropanoid CIN could interact with membrane receptors.