Isolation and identification of antifungal fatty acids from the basidiomycete Gomphus floccosus

Antifungal activity of Lysinibacillus macroides against toxigenic Aspergillus flavus and Fusarium proliferatum and analysis of its mycotoxin minimization potential

BACKGROUND

Toxigenic fungi (Aspergillus and Fusarium) and their metabolites represent the major cause of corn and corn-based products contamination and consequently lead to severe economic and health issues.

AIM

Our current study aimed to investigate the efficacy of using L. macroides Bac6 as a biological control agent against the toxigenic fungi; A. flavus f10 and F. proliferatum f30 and their mycotoxins.

RESULTS

The results illustrated that A. flavus f10 produced the aflatoxins AFB1 and AFG2 with concentrations of 21.239 and 13.593 ppb, respectively. While F. proliferatum f30 produced fumonisin B1 (9600 ppb). Furthermore, L. macroides showed a high potential for inhibition of toxigenic fungal growth using a dual culture method. F. proliferatum f30 and A. flavus f10 were found to be inhibited by a percentage of 80 and 62.5%, respectively. The results were confirmed using the scanning electron microscope. The antagonistic bacteria, L. macroides, showed chitinase productivity and activity of 26.45 U/L and 0.12 U/mL/min, respectively, which illustrates its potential application as a biocontrol agent. The GC-MS analysis revealed an abundance of Pyrrolo[1,2-a] pyrazine-1,4-dione, Hexahydro in the bacterial supernatant that exhibited antifungal characteristics. L. macroides had a significant reduction of AFB1 and AFG2 produced by A. flavus f10, recording 99.25% and 99% inhibition, respectively. It also showed strong inhibition of fumonisin B1 (90% inhibition) produced by F. proliferatum f30.

CONCLUSION

Thus, the current study is a prospective study evaluating for the first time the potential impact of L. macroides Bac6 against the toxigenic fungi and their toxins.

Characterization of triterpenoids as possible bitter-tasting compounds in teas infected with bird’s eye spot disease

Tea infected with bird's eye spot disease generally imparts a long-lasting bitter taste, which is unacceptable to most consumers. This study has comprehensively evaluated the taste profiles of infected and healthy teas and investigated their known bitter compounds previously reported in tea. Quantification analyses and calculation of dose-over-threshold (DoT) factors revealed that no obvious difference was visualized in catechins, caffeine, bitter amino acids, and flavonols and their glycosides between infected and healthy tea samples, which was also verified by principal component analysis (PCA) and hierarchical cluster analysis (HCA). Therefore, these known bitter compounds have been ruled out as critical contributors to the long-lasting bitterness of infected teas. Furthermore, Gel permeation chromatography, sensory analysis, and UPLC-Q-TOF-MS were employed and identified 13 substances from the target bitter fractions, including caffeine, ten triterpenoids, and two oxylipins. The higher triterpenoid levels were supposed to be the reason causing the long-lasting bitterness. This study has provided a research direction for the molecular basis of the long-lasting bitterness of infected tea leaves with bird's eye spot disease.

Whole-Genome Sequencing and Comparative Genomics Analysis of the Wild Edible Mushroom (Gomphus purpuraceus) Provide Insights into Its Potential Food Application and Artificial Domestication

Gomphus purpuraceus (Iwade) Yokoyama is a species of wild fungi that grows in southwest China, considered an edible and medicinal fungus with potential commercial prospects. However, the detailed mechanisms related to the development of mycelium and the formation of the fruiting body are unclear. To obtain a comprehensive overview of genetic features, whole-genome and comparative genomics analyses of G. purpuraceus were performed. High-quality DNA was extracted from the mycelium, which was isolated from a fresh fruiting body of G. purpuraceus. The DNA sample was subjected to sequencing using Illumina and Oxford Nanopore sequencing platforms. A genome assembly totaling 40.15 Mb in 50 contigs with an N50 length of 2.06 Mb was generated, and 8705 putative predicted genes were found. Subsequently, phylogenetic analysis revealed a close evolutionary relationship between G. purpuraceus and Gomphus bonarii. Moreover, a total of 403 carbohydrate-active enzymes (CAZymes) were identified in G. purpuraceus, which included 147 glycoside hydrolases (GHs), 85 glycosyl transferases (GTs), 8 polysaccharide lyases (PLs), 76 carbohydrate esterases (CEs), 57 auxiliary activities (AAs) and 30 carbohydrate-binding modules (CBMs). Compared with the other 13 fungi (Laccaria bicolor, Russula virescens, Boletus edulis, etc.), the number and distribution of CAZymes in G. purpuraceus were similar to other mycorrhizal fungi. Furthermore, the optimization of culture medium for G. purpuraceus showed the efficient utilization of disaccharides such as sucrose and maltose. The genome of G. purpuraceus provides new insights into its niche, food applications and potential artificial domestication.

The Potential of Fatty Acids and Their Derivatives as Antifungal Agents: A Review

Fungal contamination presents several problems: in humans, health issues arise from infections with opportunistic filamentous fungi and yeast, while in food, fungi cause spoilage and, in particular, in the case of mycotoxigenic fungi, can cause serious health issues. Several types of fatty acids and their derivatives, oxylipins, have been found to have inhibitory effect towards fungal growth and the production of mycotoxins. The use of fatty acids as antifungals could fulfil consumer’s requests of more natural and environmentally friendly compounds, while being less likely to promote fungal resistance. In addition, due to their nature, fatty acids are easily used as food additives. In this work, we review the most relevant and recent studies on the antifungal ability of fatty acids. We focused on saturated fatty acids, unsaturated fatty acids, and oxylipins, their different impact on fungal inhibition, their proposed modes of action, and their ability to impair mycotoxin production. Applications of fatty acids as antifungals and their limitations are also addressed.

Biting deterrency of undecanoic acid and dodecanoic acid ester analogs against Aedes aegypti

BACKGROUND

Mosquitoes remain one of the most significant threats to the health of humans throughout the world. This study was designed to evaluate the biting deterrent effects of a series of ester analogs of undecanoic acid (C:11:0) and dodecanoic acid (C:12:0) against Aedes aegypti (L), (Diptera: Culicidae), the yellow fever mosquito, using Klun and Debboun (K&D) and Ali and Khan (A&K) bioassay systems.

RESULTS

In the K&D bioassays, C:11:0 esters methyl undecanoate, propyl undecanoate, butyl undecanoate, and pentyl undecanoate, and the C:12:0 esters methyl dodecanoate, ethyl dodecanoate, propyl dodecanoate, octyl dodecanoate, and dodecyl dodecanoate were most active. All of these esters were as effective as N,N-diethyl-m-toluamide (DEET) and as effective as the parent acids undecanoic acid and dodecanoic acid with biting deterrence index values ranging from 0.80 to 0.99. In the in vitro A&K bioassay undecanoic acid with a minimum effective dose (MED) of 3.125 μg cm^-2 was the most active compound and showed higher activity than DEET (MED of 25 μg cm^-2 ). The most active synthetic analog was butyl undecanoate with a MED of 12.5 μg cm^-2 . The next most active analogs are the methyl ester analogs methyl undecanoate and methyl dodecanoate, both with MED values of 25 μg cm^-2 .

CONCLUSION

Fatty acid synthetic esters and structural analogs are a promising source of new mosquito repelling compounds and should be investigated further. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

Structure-function relationships of antifungal monohydroxy unsaturated fatty acids (HUFA) of plant and bacterial origin

This study investigated the relationships between the structures of hydroxy unsaturated fatty acids (HUFA) and their antifungal activities. Structurally diverse HUFA, including four monohydroxy-18:1 isomers, two monohydroxy 18:2 isomers and two monohydroxy 18:2 isomers were extracted from seeds of plants (Coriaria nepalensis, Thymus vulgaris, Mallotus philippensis and Dimorphotheca sinuata) for which information was available on PlantFAdb database, and from culture supernatants of lactobacilli. They were purified by high-speed counter current chromatography (HSCCC) and identified by LC-MS/MS. The minimum inhibitory concentrations of HUFA were tested against a panel of five yeasts and five mycelial fungi. The membrane phase changes under HUFA treatment and the content of ergosterol were both measured to differentiate HUFA-sensitive and HUFA-resistant fungi. HUFA with a hydroxyl group near the center of the 18-carbon fatty acid chains were found to contribute strongly to HUFA antifungal activity. Antifungal HUFA targeted filamentous fungi but not yeasts. HUFA didn't alter the overall membrane fluidity of sensitive fungi, but the most HUFA-sensitive fungi had a lower average ergosterol content compared to the resistant yeasts. This indicates the possible interaction of HUFA with fungal membrane with low sterol content, which partially support the previous proposed mode of action. Findings here provide insight on further development of HUFA application in food products.

Toxicity of secondary metabolites

Secondary metabolites, commonly referred to as natural products, are produced by living organisms and usually have pharmacological or biological activities. Secondary metabolites are the primary source for the discovery of new drugs. Furthermore, secondary metabolites are also used as food preservatives, biopesticides or as research tools. Although secondary metabolites are mainly used by their beneficial biological activity, the toxicity of some of them may limit their use. The toxicity assessment of any compound that is prone to be used in direct contact with human beings is of vital importance. There is a vast spectrum of experimental methods for toxicity evaluation, including in vitro and in vivo methodologies. In this work, we present an overview of the different sources, bioactivities, toxicities and chemical classification of secondary metabolites, followed by a sketch of the role of toxicity assessment in drug discovery and agrochemistry.

Melanogenesis Inhibitors from the Rhizoma of Ligusticum Sinense in B16-F10 Melanoma Cells In Vitro and Zebrafish In Vivo

The rhizoma of Ligusticum sinense, a Chinese medicinal plant, has long been used as a cosmetic for the whitening and hydrating of the skin in ancient China. In order to investigate the antimelanogenic components of the rhizoma of L. sinense, we performed an antimelanogenesis assay-guided purification using semi-preparative HPLC accompanied with spectroscopic analysis to determine the active components. Based on the bioassay-guided method, 24 compounds were isolated and identified from the ethyl acetate layer of methanolic extracts of L. sinense, and among these, 5-[3-(4-hydroxy-3-methoxyphenyl)allyl]ferulic acid (1) and cis-4-pentylcyclohex-3-ene-1,2-diol (2) were new compounds. All the pure isolates were subjected to antimelanogenesis assay using murine melanoma B16-F10 cells. Compound 1 and (3S,3aR)-neocnidilide (8) exhibited antimelanogenesis activities with IC₅₀ values of 78.9 and 31.1 μM, respectively, without obvious cytotoxicity. Further investigation showed that compound 8 demonstrated significant anti-pigmentation activity on zebrafish embryos (10‒20 μM) compared to arbutin (20 μM), and without any cytotoxicity against normal human epidermal keratinocytes. These findings suggest that (3S,3aR)-neocnidilide (8) is a potent antimelanogenic and non-cytotoxic natural compound and may be developed potentially as a skin-whitening agent for cosmetic uses.

Trichosanhemiketal A and B: Two 13,14-seco-13,14-epoxyporiferastanes from the root of Trichosanthes kirilowii Maxim

Of the 32 Trichosanthes species in China, T. kirilowii Maxim. is the most renowned species used in traditional Chinese medicine and has diverse pharmacological properties. However, most of the phytochemical studies of T. kirilowii have focused on the fruits and seeds. In our investigation of the chemical constituents of T. kirilowii roots, two previously undescribed sterols [trichosanhemiketal A and B (1 and 2)], together with 13 known compounds, were isolated and their structures were elucidated. To the best of our knowledge, this represents the first isolation of compounds with a 13,14-seco-13,14-epoxyporiferastane (1-2) skeleton from the Cucurbitaceae family. The anti-inflammatory activity of the isolated compounds was determined through an analysis of their inhibitory effects on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in macrophage RAW264.7 cells. Of the compounds, 4, 5, 6, and 8 showed significant inhibitory activities, with IC₅₀ values of 8.5, 15.1, 25.4, and 28.5 µM, respectively. In addition, compound 4 inhibited inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 expression in a concentration-dependent manner.

High-Speed Counter-Current Chromatography (HSCCC) Purification of Antifungal Hydroxy Unsaturated Fatty Acids from Plant-Seed Oil and Lactobacillus Cultures

Hydroxy unsaturated fatty acids (HUFA) can function as antifungal agents. To investigate the antifungal spectrum, that is, the scope of the in vitro fungal-inhibition activities of HUFA and their potential applications, three HUFA were produced by microbial transformation or extracted from plant-seed oils; these compounds included coriolic acid (13-hydroxy-9,11-octadecadienoic acid) from Coriaria seed oil, 10-hydroxy-12-octadecenoic acid from cultures of Lactobacillus hammesii, and 13-hydroxy-9-octadecenoic acid from cultures of Lactobacillus plantarum TMW1.460Δlah. HUFA were purified by high-speed counter-current chromatography (HSCCC), characterized by LC-MS and MS/MS, and their antifungal activities were evaluated with 15 indicator fungal strains. The HUFA had different antifungal spectra when compared with unsaturated fatty acids with comparable structures but without hydroxy groups. The inhibitory effects of HUFA specifically targeted filamentous fungi, including Aspergillus niger and Penicillium roqueforti, whereas yeasts, including Candida spp. and Saccharomyces spp., were resistant to HUFA. The findings here support the development of food applications for antifungal HUFA.

Fungi associated with rocks of the Atacama Desert: taxonomy, distribution, diversity, ecology and bioprospection for bioactive compounds

This study assessed the diversity of cultivable rock-associated fungi from Atacama Desert. A total of 81 fungal isolates obtained were identified as 29 Ascomycota taxa by sequencing different regions of DNA. Cladosporium halotolerans, Penicillium chrysogenum and Penicillium cf. citrinum were the most frequent species, which occur at least in four different altitudes. The diversity and similarity indices ranged in the fungal communities across the latitudinal gradient. The Fisher-α index displayed the higher values for the fungal communities obtained from the siltstone and fine matrix of pyroclastic rocks with finer grain size, which are more degraded. A total of 23 fungal extracts displayed activity against the different targets screened. The extract of P. chrysogenum afforded the compounds α-linolenic acid and ergosterol endoperoxide, which were active against Cryptococcus neoformans and methicillin-resistance Staphylococcus aureus respectively. Our study represents the first report of a new habitat of fungi associated with rocks of the Atacama Desert and indicated the presence of interesting fungal community, including species related with saprobes, parasite/pathogen and mycotoxigenic taxa. The geological characteristics of the rocks, associated with the presence of rich resident/resilient fungal communities suggests that the rocks may provide a favourable microenvironment fungal colonization, survival and dispersal in extreme conditions.

Bioactive xanthones from the roots of Hypericum perforatum (common St John's wort)

BACKGROUND

Extracts of Hypericum perforatum L. (common St John's wort; Hypericaceae) are sold as phytopharmaceuticals and herbal supplements to treat mild to moderate depression and as food additives. Extensively cultivated in Europe, plants can be infected by anthracnose (Colletotrichum gloeosporioides), a virulent fungal pathogen that causes tissue necrosis and dramatically decreases crop value. Such infections triggered the production of new secondary metabolites, specifically xanthones, in cell culture experiments.

RESULTS

Bioassay-guided fractionation of H. perforatum root extracts, testing for growth inhibition of plant pathogenic fungi from the genera Colletotrichum, Botrytis, Fusarium and Phomopsis, was performed. In vitro anti-inflammatory activity through inhibition of COX-1, COX-2 and 5-LOX-catalyzed LTB(4) formation was also evaluated. Extracts were analyzed by various chromatographic means and structure elucidation was performed using data from nuclear magnetic resonance and mass spectrometry.

CONCLUSION

Researchers have previously described constituents from the aerial parts of this species, but few reports describe secondary metabolites found in underground parts, of particular interest because the lower stem and upper root are often sites of fungal infection. This work resulted in the isolation of three xanthones: 1,6-dihydroxy-5-methoxy-4',5'-dihydro-4',4',5'-trimethylfurano-(2',3':3,4)-xanthone; 4,6-dihydroxy-2,3-dimethoxyxanthone; and cis-kielcorin, one of which possessed novel bioactivity against species of Phomopsis and inhibited 5-LOX-mediated LTB(4) formation.

A survey of phytotoxic microbial and plant metabolites as potential natural products for pest management

Phytotoxic microbial metabolites produced by certain phytopathogenic fungi and bacteria, and a group of phytotoxic plant metabolites including Amaryllidacea alkaloids and some derivatives of these compounds were evaluated for algicide, bactericide, insecticide, fungicide, and herbicide activities in order to discover natural compounds for potential use in the management and control of several important agricultural and household structural pests. Among the various compounds evaluated: i) ophiobolin A was found to be the most promising for potential use as a selective algicide; ii) ungeremine was discovered to be bactericidal against certain species of fish pathogenic bacteria; iii) cycasin caused significant mortality in termites; iv) cavoxin, ophiobolin A, and sphaeropsidin A were most active towards species of plant pathogenic fungi; and v) lycorine and some of its analogues (1-O-acetyllycorine and lycorine chlorohydrate) were highly phytotoxic in the herbicide bioassay. Our results further demonstrated that plants and microbes can provide a diverse and natural source of compounds with potential use as pesticides.

Natural toxins for use in pest management

Natural toxins are a source of new chemical classes of pesticides, as well as environmentally and toxicologically safer molecules than many of the currently used pesticides. Furthermore, they often have molecular target sites that are not exploited by currently marketed pesticides. There are highly successful products based on natural compounds in the major pesticide classes. These include the herbicide glufosinate (synthetic phosphinothricin), the spinosad insecticides, and the strobilurin fungicides. These and other examples of currently marketed natural product-based pesticides, as well as natural toxins that show promise as pesticides from our own research are discussed.