Spore Germination Research Articles

Proteomics analysis reveals the inactivation mechanisms of Alicyclobacillus acidoterrestris spores by atmospheric cold plasma

SummaryAlicyclobacillus acidoterrestris is a typical endospore‐forming microorganism, whose spores are able to germinate in Not From Concentrate juice causing its spoilage. In this work, dielectric barrier discharge atmospheric cold plasma (DBD‐ACP) at the voltage of 30 kV was used to inactivate Alicyclobacillus acidoterrestris spores in NFC juice (2–8 min). The results showed spores reduced nearly 3‐log CFU mL−1 after 8 min treatment, and the morphology of spores were severely disrupted, causing the release of their contents. Furthermore, proteomic analysis showed totals of 122 and 170 different expression proteins were detected in group C (control)/Ct1 (30 kV, 4 min) and C/Ct2 (30 kV, 8 min), respectively, indicating that metabolic activities of spores including amino acid and energy metabolic, protein biosynthesis, DNA replication and spore germination are inhibited. This study confirms the inactivation of Alicyclobacillus acidoterrestris spores by DBD‐ACP and provides some new perspectives on the inactivation mechanisms of spores by DBD‐ACP.

A Transient Spore‐Forming Microbial Fuel Cell with Extracellularly Biosynthesized Tin Oxide Nanoparticles for Powering Disposable and Green Papertronics

AbstractTransient electronics, which can operate only for short‐lived applications and then be eco‐friendly disintegrated, create opportunities in environmental sensing, healthcare, and hardware security. Paper‐based electronics, or papertronics, recently have rapidly advanced the physically transient device platform because paper as a foundation offers an environmentally sustainable and cost‐effective option for those increasingly pervasive and fast‐updated single‐use applications. Paper‐based power supplies are indispensable to realize a fully papertronic paradigm and are a critical enabler of environmentally benign power solutions. Microbial fuel cells (MFCs) hold great potential as power sources for such green papertronic applications. This work reports the design, operation, and optimization of a high‐power papertronic MFC by biosynthesizing microbe‐mediated tin oxide nanoparticles (SnO2 NPs) on dormant Bacillus subtilis endospores. They form an electrical conduit that improves electron harvesting during the spore germination and power generation. The MFC is packaged in a sub‐microporous alginate to minimize the potential risk of bacteria leakage. Upon the introduction of water, the paper‐based MFC generates a significantly enhanced power density of 140 µW cm−2, which is more than two orders of magnitude greater than their previously reported counterparts. Six MFCs connected in series generate more than sufficient power to run an on‐chip, light‐emitting diode.

Identification of lncRNA and weighted gene coexpression network analysis of germinating Rhizopus delemar causing mucormycosis

ABSTRACT Rhizopus delemar, an opportunistic fungal pathogen, causes a highly fatal disease, mucormycosis. Spore germination is a crucial mechanism for disease pathogenesis. Thus, exploring the molecular mechanisms of fungal germination would underpin our knowledge of such transformation and, in turn, help control mucormycosis. To gain insight into the developmental process particularly associated with cell wall modification and synthesis, weighted gene co-expression network analysis (WGCNA) was performed including both coding and non-coding transcripts identified in the current study, to find out the module of interest in the germination stages. The module-trait relationship identified a particular module to have a high correlation only at the resting phase and further analysis revealed the module to be enriched for protein phosphorylation, carbohydrate metabolic process, and cellular response to stimulus. Moreover, co-expression network analysis of highly connected nodes revealed cell wall modifying enzymes, especially those involved in mannosylation, chitin-glucan crosslinking, and polygalacturonase activities co-expressing and interacting with the novel lncRNAs among which some of them predicted to be endogenous target mimic (eTM) lncRNAs. Hence, the present study provides an insight into the onset of spore germination and the information on the novel non-coding transcripts with key cell wall–related enzymes as potential targets against mucormycosis.

Understanding Environmental and Physiological Factors Affecting the Biology of Diaporthe ilicicola, the Fungus Causing Latent Fruit Rot in Winterberry.

Fruit rot in winterberry is associated with a complex of fungal pathogens. Among them, Diaporthe ilicicola plays a unique role by infecting flowers at bloom, resulting in symptom development in mature fruit. This research aimed to identify at what stage of maturation Ilex fruit can develop disease symptoms and correlate changes in fruit physiology (sugar and phenolic content) and environment (temperature and light intensity) with disease incidence. Correlation data informed in vitro studies testing the ability of putative factors to alter growth of D. ilicicola and select opportunistic fungi within the fruit rot complex: Alternaria alternata, Colletotrichum fioriniae, and Epicoccum nigrum. Results indicated that Ilex fruit do not develop symptoms until 81 to 108 days after inoculation. Temperature and fruit phenolic content were negatively correlated with disease incidence, while fruit sugar concentration and light intensity were positively correlated. In vitro assays revealed that sugar concentration had no effect on the growth of D. ilicicola, but increased light intensity increased hyphal growth and pycnidium formation. Additionally, phenolics extracted from fruit inhibited spore germination in A. alternata, induced secondary conidiation in C. fioriniae, and late season phenolic extracts increased hyphal melanization and pycnidial formation in D. ilicicola. Finally, drops in field temperatures, when replicated in vitro, resulted in a decrease in hyphal growth and spore germination for all fungi. These results suggest that changes in Ilex fruit phenolics during maturation and the increased exposure to light following defoliation may play a role in symptom development by altering D. ilicicola growth within the fruit.

Genome analysis of Tepidibacter sp. SWIR-1, an anaerobic endospore-forming bacterium isolated from a deep-sea hydrothermal vent.

Tepidibacter sp. SWIR-1, a putative new species isolated from deep-sea hydrothermal vent field on the Southwest Indian Ridge (SWIR), is an anaerobic, mesophilic and endospore-forming bacterium belonging to the family Peptostreptococcaceae. In this study, we present the complete genome sequence of strain SWIR-1, consists of a single circular chromosome comprising 4,122,966 nucleotides with 29.25% G+C content and a circular plasmid comprising 38,843 nucleotides with 29.46% G+C content. In total, 3861 protein coding genes, 104 tRNA genes and 46 rRNA genes were obtained. SWIR-1 genome contains numerous genes related to sporulation and germination. Compared with the other three Tepidibacter species, SWIR-1 contained more spore germination receptor proteins. In addition, SWIR-1 contained more genes involved in chemotaxis and two-component systems than other Tepidibacter species. These results indicated that SWIR-1 has developed versatile adaptability to the Southwest Indian Ridge hydrothermal vent environment. The genome of strain SWIR-1 will be helpful for further understanding adaptive strategies used by bacteria dwelling in the deep-sea hydrothermal vent environments of different oceans.

Are Histidine Kinases of Arbuscular Mycorrhizal Fungi Involved in the Response to Ethylene and Cytokinins?

Signals are exchanged at all stages of the arbuscular mycorrhizal (AM) symbiosis between fungi and their host plants. Root-exuded strigolactones are well-known early symbiotic cues, but the role of other phytohormones as interkingdom signals has seldom been investigated. Here we focus on ethylene and cytokinins, for which candidate receptors have been identified in the genome of the AM fungus Rhizophagus irregularis. Ethylene is known from the literature to affect asymbiotic development of AM fungi, and in the present study, we found that three cytokinin forms could stimulate spore germination in R. irregularis. Heterologous complementation of a Saccharomyces cerevisiae mutant strain with the candidate ethylene receptor RiHHK6 suggested that this protein can sense and transduce an ethylene signal. Accordingly, its N-terminal domain expressed in Pichia pastoris displayed saturable binding to radiolabeled ethylene. Thus, RiHHK6 displays the expected characteristics of an ethylene receptor. In contrast, the candidate cytokinin receptor RiHHK7 did not complement the S. cerevisiae mutant strain or Medicago truncatula cytokinin receptor mutants and seemed unable to bind cytokinins, suggesting that another receptor is involved in the perception of these phytohormones. Taken together, our results support the hypothesis that AM fungi respond to a range of phytohormones and that these compounds bear multiple functions in the rhizosphere beyond their known roles as internal plant developmental regulators. Our analysis of two phytohormone receptor candidates also sheds new light on the possible perception mechanisms in AM fungi. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Citrus lemon (Citrus limon (L.) Burm. f. cv. Eureka) essential oil controls blue mold in citrus by damaging the cell membrane of Penicillium italicum

As a major postharvest pathogenic fungus of citrus fruit, Penicillium italicum (P. italicum) can cause significant economic losses to the citrus fruit industry. By using steam distillation, we extracted 14 kinds of domestic citrus peel essential oils (EOs) and analyzed the antifungal inhibitory activity of different varieties of EOs. The results showed that Citrus lemon (YLK) EO was the most effective in inhibiting the growth of P. italicum with an MIC and MFC of 0.625 mg/mL and 1.25 mg/mL, respectively. Forty volatile components were identified in YLK EO, and the most prevalent were limonene (46.2%), gamma-terpinene (12.16%), pinene (11.07%), and citral (3.47%). YLK EO treatment significantly inhibited P. italicum spore germination and mycelial growth, disrupted mycelial morphology, and caused reactive oxygen species accumulation and membrane lipid peroxidation in vitro. All these changes disrupt the integrity and permeability of the cell membrane. In addition, in vivo, YLK EO treatment could effectively control and retard the growth and reproduction of P. italicum in citrus fruits. Based on these findings, we can conclude that YLK EO exhibits potent antifungal activity against P. italicum. Its potential antifungal mechanism is likely associated with the damage inflicted on the cell membrane. Therefore, YLK EO can be considered a potential source of natural antifungal agents.

Characterization of Trichoderma species from forest ecosystems by high-throughput phenotypic microarray

The use of beneficial organisms for the biocontrol of soil-borne pathogens in forestry is still poor explored. In this work, the nutritional demands of 10 previously selected isolates of Trichoderma for the biocontrol of forest soil-borne pathogens have been tested by Phenotype Microarray technology, to investigate about their C-source utilization and exploring the possibility to obtain a microbial consortia (SynCom), an innovative strategy for the biocontrol of plant disease. All Trichoderma isolates tested in this study showed a high spore germination percentage within 3 d and evidenced nutritional preference regardless of the species they belong to, and unrelated to their soil of origin. Results of growth curve analysis and MANOVA test revealed that all isolates assimilate a broad range of substrates, generally preferring complex compounds such as monosaccharides related compounds, nitrogen compounds, carboxylic acids and esters. No evidence of competition for nutritional resources have been observed among isolates of this study. As a result, a combination of different isolates could be proposed to obtain a SynCom useful for the practice of phytopathogen biocontrol in forestry. The addition of i-erythritol, adenosine and turanose to a growth substrate could be suggested as stimulating compounds for the growth of the selected Trichoderma isolates.

Identification and fungicide control of Bipolaris sorokiniana causing leaf spot and blight on common hop (Humulus lupulus) in Korea.

Hop (Humulus lupulus) is a perennial herbaceous vine belonging to the family Cannabeaceae. This crop is commercially grown for the brewing industry for its bitter and aromatic flavor, as well as its antiseptic properties. In June 2021, leaf spot and blight was observed on common hop plants in Buan-gun, Jeollabuk-do, South Korea. The typical symptoms were small to large, dark brown necrotic lesions with yellow halos on the leaves. This study aimed to clarify the causal agent of this disease. Two fungal species, Alternaria alternata and Bipolaris sorokiniana, were isolated from the diseased leaf samples and identified by combining morphological observations and phylogenetic analysis using sequence datasets of ITS, Alt a1, rpb2, endoPG, OPA10-2, and ITS, gpd, and tef1, respectively. Pathogenicity of the fungal isolates on detached leaves and living plants revealed that B. sorokiniana is the causal pathogen of this disease, while A. alternata is potentially a saprophyte. Fungicide sensitivity of the pathogen B. sorokiniana was further estimated in vitro using three classes of fungicides represented by fluxapyroxad, pyraclostrobin, and hexaconazole. The effective concentrations that inhibited 50% of spore germination (EC50) were 0.72 µg ml-1, 1.90 µg ml-1, and 0.68 µg ml-1, respectively. Moreover, all of these fungicides were able to control B. sorokiniana on detached common hop leaves at their recommended concentrations. In conclusion, this study reports leaf spot and blight of common hop caused by B. sorokiniana for the first time and proposes potential fungicides for this disease.

Biological control of maize downy mildew with the antagonistic bacterial consortium

Abstract. Mugiastuti E, Manan A, Soesanto L. 2023. Biological control of maize downy mildew with the antagonistic bacterial consortium. Biodiversitas 24: 4644-4650. Downy mildew is one of the main diseases of maize, which is a limiting factor for maize production in Indonesia. With a consortium of maize-indigenous antagonist bacteria, biological control is expected to reduce downy mildew. The aim of this research was to determine the ability of three antagonistic bacteria Bacillus amyloliquefaciens BB.R3, Bacillus subtilis BB.B4, Pseudomonas putida BB.R1 in suppressing spore germination of Peronoslerospora spp., and to evaluate the ability of their consortium in controlling downy mildew and promote the growth of maize. Based on the research results, antagonistic bacteria B. amyloliquefaciens BB.R3, B. subtilis BB.B4, and P. putida BB.R1 were able to suppress spore germination by 76.68-100%. The bacterial consortium of Bacillus subtilis BB. B4 + Pseudomonas putida BB.R1 was the best consortium of antagonistic bacteria and had the most potential to developed as a downy mildew control and promote the growth of maize. This bacterial consortium delayed the incubation period, lowered the intensity of the disease (85.77%) and AUDPC (83.02%), increased the content of phenols (tannins, glycosides, and saponins), and promoted plant growth (plant height 138.10%, the number of leaves 102.29%, root length 219.89%, fresh plant weight 1091.81%, and dry plant weight 1077.04%) compared to the control. Treatment with antagonistic bacteria showed better results compared to the fungicide metalaxyl. Based on the results, applying antagonistic bacteria consortium is a potential strategy to control maize downy mildew.

The Role of Fatty Acids from Plant Surfaces in the Infectivity of Colletotrichum fioriniae.

Aqueous extracts derived from flowers stimulate germination, secondary conidiation, and appressorial formation of various latent fruit rotting fungi. Even raindrops passing over flowers accumulate sufficient activity to influence the infectivity of fruit rotting fungi. Using a spore germination bioassay, high levels of bioactivity were found in chloroform extracts from plant tissues, implicating the nonpolar components of the cuticle. The fatty acid (FA) and fatty acid methyl ester (FAME) composition (C9-C20) of blueberry and cranberry tissues as well as aqueous flower extracts were characterized using a gas chromatography-mass spectrometry (GC-MS) method. The FAs and FAMEs found in the plant extracts were then tested for bioactivity using a spore germination bioassay. The C16:0 and C18:2 FAs and FAMEs, as well as the C18:0 FAME and the C20:0 FA, all stimulated appressorial formation while the C10:0 FA stimulated secondary conidiation. The C10:0 and C16:0 FAs were the only two bioactive components also identified from the aqueous floral extracts of both blueberry and cranberry and are therefore considered as contributors to the bioactivity observed in these extracts. The aqueous extracts from surfaces other than flowers showed little or no activity, and it is speculated that the movement of FAs may be related to the level of polymerization and cutin polyester development in flowers versus other plant organs. This study highlights the importance of the bloom period for infection and that the apparent effects on host susceptibility may therefore depend on the availability of specific FAs or combinations thereof.

Postharvest mycobial contaminants of white button mushroom (Agaricus bisporus) and their management using plant essential oils

Being highly perishable, mushrooms’ quality and shelf life is affected by various factors during postharvest conditions, among which fungal contamination is the main cause. The goal of this study is to identify and manage fungal contaminants present in mushrooms during postharvest conditions. A total of 23 fungi were isolated as contaminants from the samples of Agaricus bisporus collected from three major vegetable markets in Kathmandu city, Nepal. Aspergillus niger, Aspergillus flavus, and Rhizopus stolonifer were found to be the most frequent fungal contaminants. These were treated with various concentrations of essential oils (EOs) of Cinnamomum tamala, Mentha spicata, Zanthoxylum armatum, and Eucalyptus citriodora using poisoned food technique. Significant (p<0.05) inhibition of mycelial growth and spore germination was found in all testedfungi by all EOs. A strong inhibitory action of M. spicata oil was recorded against A. flavus and R. stolonifer while, A. niger was best controlled by C. tamala oil at the concentration of 20 µl/ml. These results suggest that EOs of three tested plants could be a good alternative to control fungal contaminants and extend the shelf life of Agaricus bisporus in postharvest conditions.

Effect of chilled storage on the quality, in-vitro protein digestibility, and microbial growth of sous vide processed beef short ribs pre-treated with pulsed electric field (PEF)

Sous vide (60 °C/24 h) processed beef short ribs pre-treated with Pulsed Electric Field (electric field strength: 0.65–0.80 kV/cm, specific energy: 87.00–102.39 kJ/kg) were stored at 4 °C for 42 days. Cooking loss, Texture Profile Analysis (TPA) parameters, colour, lipid and protein oxidation, in vitro protein digestibility and microbial growth were assessed. Storage time significantly (p < 0.05) affected TPA hardness, cohesiveness, springiness, and gumminess, but had no effect on adhesiveness and colour parameters. Lipid and protein oxidation significantly (p < 0.05) increased during storage. In vitro protein digestibility significantly (p < 0.05) decreased after 42 days of chilled storage. Aerobic and anaerobic microbial numbers were found below detection limit (102 CFU/g meat) until 21 and 42 days, respectively. The detection of bacteria after 21 days of storage was believed to be due to the germination and growth of spore forming bacterial capable of growth at 4 °C, which if present will limit the shelf life. Industrial relevanceThis information provides practical industry evidence on the shelf life of PEF-SV processed short ribs during chilled (4 °C) storage. Three-layer plastic and aluminum laminate packaging could maintain the quality and safety of the product. No microbial growth was detected up to three weeks of chilled storage. Prolonging storage time affects the texture properties of PEF-SV processed short ribs (SR) but not the meat colour.

Co-evolution at protein-protein interfaces guides inference of stoichiometry of oligomeric protein complexes by de novo structure prediction.

The quaternary structure with specific stoichiometry is pivotal to the specific function of protein complexes. However, determining the structure of many protein complexes experimentally remains a major bottleneck. Structural bioinformatics approaches, such as the deep learning algorithm Alphafold2-multimer (AF2-multimer), leverage the co-evolution of amino acids and sequence-structure relationships for accurate de novo structure and contact prediction. Pseudo-likelihood maximization direct coupling analysis (plmDCA) has been used to detect co-evolving residue pairs by statistical modeling. Here, we provide evidence that combining both methods can be used for de novo prediction of the quaternary structure and stoichiometry of a protein complex. We achieve this by augmenting the existing AF2-multimer confidence metrics with an interpretable score to identify the complex with an optimal fraction of native contacts of co-evolving residue pairs at intermolecular interfaces. We use this strategy to predict the quaternary structure and non-trivial stoichiometries of Bacillus subtilis spore germination protein complexes with unknown structures. Co-evolution at intermolecular interfaces may therefore synergize with AI-based de novo quaternary structure prediction of structurally uncharacterized bacterial protein complexes.

Effect of a harsh circular environment on self-healing microbial-induced calcium carbonate materials for preventing Pb2+ migration

Microbially induced carbonate precipitation (MICP) is increasingly being explored for Pb-contaminated water bodies and soil remediation. However, the Pb-related precipitate resulting from the MICP process can possibly leach acid over time when subjected to harsh environments, causing serious threats to human health. In this study, for the first time, self-healing microbial-induced calcium carbonate (MICC) materials are proposed and applied to prevent Pb2+ migration where the Pb-related precipitate is acid leached after spore germination, spore-vegetative cell transformation, urease secretion, and urea hydrolysis, thereby producing spore-containing precipitation. This process was repeated five times to explore the effect of a harsh circular environment on self-healing MICC materials. Results indicated that Pb immobilization would have deteriorated if the inosine and trace elements had not been intervened during spore germination and spore-vegetative cell transformation, respectively. The spores and vegetative cells provided extra nucleation sites for Pb2+ and minerals to attach. The extracellular polymeric substances (EPSs) combined Pb2+ with functional groups and chemical bonds to prevent their migration to surrounding environments. The scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDS) images also indicated that the cerussite mineral was precipitated prior to the calcite mineral because Pb2+ had more affinity to combine with CO32- and OH-. An immobilization efficiency of greater than 95% remained nearly the same after five cycles, while it reduced very quickly to less than 10% after three cycles when neglecting the self-healing MICC materials, thus highlighting their relative merits.

Volatile Organic Compounds of Scheffersomyces spartinae W9 Have Antifungal Effect against Botrytis cinerea on Strawberry Fruit.

This study aims to evaluate the antifungal effects of volatile organic compounds (VOCs) produced by a marine biocontrol yeast, Scheffersomyces spartinae W9. The results showed that the VOCs from the yeast inhibited the growth of Botrytis cinerea mycelium and spore germination by 77.8% and 58.3%, respectively. Additionally, it reduced the disease incidence and lesion diameter of gray mold on the strawberry fruit surface by 20.7% and 67.4%, respectively. Electronic micrographs showed that VOCs caused damage to the morphology and ultrastructure of the hyphae. Based on headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME/GC-MS), S. spartinae W9 emitted 18 main VOCs, and the pure substance of VOCs, such as 3-methyl-1-butanol, 2-methyl-1-butanol, 2-phenylethanol, and isoamyl acetate, showed antifungal effects against B. cinerea mycelium growth. Among them, 2-phenylethanol exhibited the strongest antifungal activity. It has been concluded that VOCs are the key antifungal mechanism of S. spartinae W9, and a promising strategy for controlling gray mold on strawberry fruit.

Correlating Antibiotic-Induced Dysbiosis to Clostridioides difficile Spore Germination and Host Susceptibility to Infection Using an Ex Vivo Assay.

Antibiotic-induced microbiota disruption and its persistence create conditions for dysbiosis and colonization by opportunistic pathogens, such as those causing Clostridioides difficile (C. difficile) infection (CDI), which is the most severe hospital-acquired intestinal infection. Given the wide differences in microbiota across hosts and in their recovery after antibiotic treatments, there is a need for assays to assess the influence of dysbiosis and its recovery dynamics on the susceptibility of the host to CDI. Germination of C. difficile spores is a key virulence trait for the onset of CDI, which is influenced by the level of primary vs secondary bile acids in the intestinal milieu that is regulated by the microbiota composition. Herein, the germination of C. difficile spores in fecal supernatant from mice that are subject to varying degrees of antibiotic treatment is utilized as an ex vivo assay to predict intestinal dysbiosis in the host based on their susceptibility to CDI, as determined by in vivo CDI metrics in the same mouse model. Quantification of spore germination down to lower detection limits than the colony-forming assay is achieved by using impedance cytometry to count single vegetative bacteria that are identified based on their characteristic electrical physiology for distinction vs aggregated spores and cell debris in the media. As a result, germination can be quantified at earlier time points and with fewer spores for correlation to CDI outcomes. This sets the groundwork for a point-of-care tool to gauge the susceptibility of human microbiota to CDI after antibiotic treatments.

Development of antifungal electrospun nanofiber mats containing Meyerozyma caribbica

To mitigate vegetable and fruit loss caused by post-harvest fungal diseases, polymeric antifungal coatings encapsulating biocontrol yeasts offer a sustainable alternative. Nanofibers derived from pullulan, cashew gum, FucoPol and poly (ethylene oxide) (PEO), were electrospun and loaded with Meyerozyma caribbica (GenBank ID: JQ398674). The morphological, thermal and chemical properties of cashew gum (CG:PEO), FucoPol (FP:PEO), and pullulan nanofibers were characterized. The viability of M. caribbica within the fibers and their in vitro antifungal activity against six phytopathogens were assessed. Morphological analysis exhibited the presence of nanofibers encapsulating M. caribbica. ATR-FTIR spectroscopy identified the absence of interactions between the yeast and polymers. Fibers containing M. caribbica exhibited in vitro fungistatic effects on spore germination. Pullulan nanofibers showed the highest M. caribbica viability and the highest percentage of growth inhibition against the evaluated fungi. These promising nanofibers encapsulating biocontrol yeasts could be used as edible coatings or agricultural aids, which offer an alternative for post-harvest treatment to control fungal diseases, reducing global food loss.

Natural Product Aloesin Significantly Inhibits Spore Germination and Appressorium Formation in Magnaporthe oryzae.

This study aims to determine the effects of the natural product aloesin against Magnaporthe oryzae. The results exposed that aloesin had a high inhibitory effect on appressorium formation (the EC50 value was 175.26 μg/mL). Microscopic examination revealed that 92.30 ± 4.26% of M. oryzae spores could be broken down by 625.00 μg/mL of aloesin, and the formation rate of appressoria was 4.74 ± 1.00% after 12 h. M. oryzae mycelial growth was weaker than that on the control. The enzyme activity analysis results indicated that aloesin inhibited the activities of polyketolase (PKS), laccase (LAC), and chain-shortening catalytic enzyme (Aayg1), which are key enzymes in melanin synthesis. The inhibition rate by aloesin of PKS, LAC, and Aayg1 activity was 32.51%, 33.04%, and 43.38%, respectively. The proteomic analysis showed that actin expression was downregulated at 175.62 μg/mL of aloesin, which could reduce actin bundle formation and prevent the polar growth of hyphae in M. oryzae. This is the first report showing that aloesin effectively inhibits conidia morphology and appressorium formation in M. oryzae.

Development of konjac glucomannan based Syringa essential oil film and its fragmented form for quality maintenance of citrus fruits

Citrus fruits have suffered serious losses in postharvest storage and transportation. A novel approach, fragmented konjac glucomannan-based Syringa essential oil (KSE) films, was used to maintain the quality of citrus fruits in storage. The KSE film was successfully prepared by using the encapsulating method via coacervation, with an encapsulation efficiency of 18.3% and loading capacity of 11.4%. GC–MS showed that eugenol, caryophyllene, and humulene were the main constituents of Syringa EO. SEM showed that EO drops or volatiles distributed in the KGM molecular matrix produced a concave structure during film formation. FTIR indicated no interaction or modification between KGM and Syringa EO, and EO was successfully encapsulated into the KGM films. The fragmented KSE films showed significant antifungal activity against Penicillium italicum, Penicillium digitatum, and Geotrichum citri-aurantii, inhibiting spore germination and mycelium elongation, resulting in suspected indentation, plasmolysis, and vacuolization. In storage, the fragmented KSE film packed in a non-woven bag apparently maintained the quality of citrus fruits, including sustaining fruit firmness and reducing vitamin C (VC), total soluble solids (TSS), and titratable acid (TA) loss. One of the modes of action for the quality maintenance of citrus fruits might be induced systemic resistance. This study might convey stronger impact in postharvest by newly developed packaging materials.