Xiaohan Wang

Bis-naphtho-γ-pyrones from Fungi and Their Bioactivities

Bis-naphtho-γ-pyrones are an important group of aromatic polyketides derived from fungi. They have a variety of biological activities including cytotoxic, antitumor, antimicrobial, tyrosine kinase and HIV-1 integrase inhibition properties, demonstrating their potential applications in medicine and agriculture. At least 59 bis-naphtho-γ-pyrones from fungi have been reported in the past few decades. This mini-review aims to briefly summarize their occurrence, biosynthesis, and structure, as well as their biological activities. Some considerations regarding to synthesis, production, and medicinal and agricultural applications of bis-naphtho-γ-pyrones are also discussed.

Bioactive Spirobisnaphthalenes from the Endophytic Fungus Berkleasmium sp.

Nine new spirobisnaphthalenes, palmarumycins B1-B9 (1-9), along with 13 known compounds (10-22), were isolated from cultures of the fungus Berkleasmium sp., an endophyte isolated from the medicinal plant Dioscorea zingiberensis C. H. Wright. The structures of the new compounds were elucidated by analysis of the 1D and 2D NMR and HRESIMS spectra and by comparison with known compounds. Compounds 7-9 contain an uncommon 2,3-dihydro-1H-inden-1-one unit. All isolated compounds were evaluated for their antibacterial activities against Bacillus subtilis, Staphylococcus hemolyticus, Agrobacterium tumefaciens, Pseudomonas lachrymans, Ralstonia solanacearum, and Xanthomonas vesicatoria and for their antifungal effects against the spore germination of Magnaporthe oryzae. Palmarumycin C8 (22) exhibited the best antibacterial and antifungal effects. In addition, diepoxin δ (11) and palmarumycin C8 (22) showed pronounced cytotoxic activities against five human cancer cell lines (HCT-8, Bel-7402, BGC-823, A 549, A 2780) with IC50 values of 1.28-5.83 μM.

Bioactive Bis-naphtho-γ-pyrones from Rice False Smut Pathogen Ustilaginoidea virens

Ustilaginoidins were bis-naphtho-γ-pyrones mycotoxins possessing an aR configuration of the chiral axis previously reported from the false smut balls of rice infected by the fungal pathogen Ustilaginoidea virens. To investigate the chemical diversity of these metabolites and their bioactivities, we fermented this fungus on solid rice media, which afforded the isolation of 13 ustilaginoidins, including seven new compounds, namely ustilaginoidins K-P, 1-6, and E1, 7, together with the known ustilaginoidins A, 8, D, 9, E, 10, F, 11, and G, 12, and isochaetochromin B2, 13. The structures of the new compounds were elucidated by using (1D, 2D) NMR, high-resolution mass spectrometry, UV, and circular dichroism, as well as by comparison with the literature data. A plausible biosynthesis pathway was proposed for these dimeric polyketides. The isolated compounds were evaluated for their antibacterial, cytotoxic, and radicle elongation inhibitory activities. Ustilaginoidins K, 1 and L, 2 showed cytotoxic activities on the A2780 human ovarian cancer cell line with IC50 values of 4.18 and 7.26 μM, respectively. Ustilaginoidins N, 4, D, 9, E, 10, and G, 12 were active against the tested pathogenic bacteria with MIC values in the range of 16-64 μg/mL. Ustilaginoidins O, 5, E, 10, and F, 11, and isochaetochromin B2, 13 displayed moderate inhibitory activity on the radicle elongation of rice seeds.

Purification of Ustiloxins A and B from Rice False Smut Balls by Macroporous Resins

Ustiloxins are cyclopeptide mycotoxins produced by Villosiclava virens, the pathogenic fungus of rice false smut disease. Both resins SP207 and SP700 were screened to show the best adsorption and desorption properties for ustiloxins A and B among 20 commercial macroporous resins. Dynamic adsorption and desorption tests were carried out to optimize the process parameters. The optimal conditions for adsorption of resin SP207 were a processing volume as 32 bed volumes (BV), pH value of 4, and flow rate of 2 BV/h; and those for desorption of resin SP207 were a 40:60 (v/v) ratio of ethanol to water, an eluent volume of 4 BV, pH value of 4 and a flow rate of 3 BV/h. The optimal conditions for adsorption of resin SP700 were a processing volume of 26 BV, pH value as 4, flow rate of 2 BV/h; and those for desorption of resin SP700 were a 30:70 (v/v) ratio of ethanol to water solution as eluent, volume of 4 BV, pH value as 4 and flow rate of 2 BV/h. Under the optimal conditions; the purities of ustiloxins A and B obtained with resin SP207 increased 23.06-fold and 19.78-fold, respectively; and their recoveries were 96.67% and 81.25%; respectively. Similarly; the purities of ustiloxins A and B obtained with resin SP700 increased 14.75-fold and 15.33-fold and their recoveries were 93.65% and 88.64%; respectively. The results show that adsorption and desorption on SP207 and SP700 resins are effective strategies for purifying ustiloxins A and B. The developed methods are beneficial for large-scale preparation and purification of ustiloxins A and B from rice false smut balls.

Development of a Monoclonal Antibody-Based icELISA for the Detection of Ustiloxin B in Rice False Smut Balls and Rice Grains

Rice false smut is an emerging and economically-important rice disease caused by infection by the fungal pathogen Villosiclava virens. Ustiloxin B is an antimitotic cyclopeptide mycotoxin isolated from the rice false smut balls that formed in the pathogen-infected rice spikelets. A monoclonal antibody (mAb) designated as mAb 1B5A10 was generated with ustiloxin B—ovalbumin conjugate. A highly-sensitive and specific indirect competitive enzyme-linked immunosorbent assay (icELISA) was then developed. The median inhibitory concentration (IC50) of the icELISA was 18.0 ng/mL for the detection of ustiloxin B; the limit of detection was 0.6 ng/mL, and the calibration range was from 2.5 to 107.4 ng/mL. The LOD/LOQ values of the developed ELISA used for the determination of ustiloxin B in rice false smut balls and rice grains were 12/50 μg/g and 30/125 ng/g, respectively. The mAb 1B5A10 cross-reacted with ustiloxin A at 13.9% relative to ustiloxin B. Average recoveries of ustiloxin B ranged from 91.3% to 105.1% for rice false smut balls at spiking levels of 0.2 to 3.2 mg/g and from 92.6% to 103.5% for rice grains at spiking levels of 100 to 5000 ng/g. Comparison of ustiloxin B content in rice false smut balls and rice grains detected by both icELISA and high performance liquid chromatography (HPLC) demonstrated that the developed icELISA can be employed as an effective and accurate method for the detection of ustiloxin B in rice false smut balls, as well as rice food and feed samples.

Sorbicillinoids from Fungi and Their Bioactivities

Sorbicillinoids are important hexaketide metabolites derived from fungi. They have a variety of biological activities including cytotoxic, antioxidant, antiviral and antimicrobial activity. The unique structural features of the sorbicillinoids make them attractive candidates for developing new pharmaceutical and agrochemical agents. About 90 sorbicillinoids have been reported in the past few decades. This mini-review aims to briefly summarize their occurrence, structures, and biological activities.

Main Ustilaginoidins and Their Distribution in Rice False Smut Balls

Rice false smut has become an increasingly serious fungal disease in rice (Oryza sativa L.) production worldwide. Ustilaginoidins are bis-naphtho-γ-pyrone mycotoxins previously isolated from the rice false smut balls (FSBs) infected by the pathogen Villosiclava virens in rice spikelets on panicles. To investigate the main ustilaginoidins and their distribution in rice FSBs, five main bis-naphtho-γ-pyrones, namely ustilaginoidins A (1), G (2), B (3), I (4) and C (5), were isolated and identified by NMR and high-resolution mass spectrometry as well as by comparison with the data in the literature. The rice FSBs at early, middle and late maturity stages were divided into their different parts and the contents of five main ustilaginoidins for each part were determined by HPLC analysis. The results revealed that the highest levels of ustilaginoidins were in late stage rice FSBs, followed by those at middle stage. Most ustilaginoidins, 96.4% of the total quantity, were distributed in the middle layer at early stage. However, ustilaginoidins were mainly distributed in the outer and middle layers at middle and late stages. Small amounts of ustilaginoidins A (1) and G (2) were found in the inner part of rice FSBs at each maturity stage. The contents of ustilaginoidins A (1) and G (2) without hydroxymethyl groups at C-2 and C-2’ of the γ-pyrone rings in rice FSBs were relatively high at early stage, while the contents of ustilaginoidins B (3), I (4), and C (5) with hydroxymethyl groups at C-2 or C-2’ were relatively high at late stage.

A monoclonal antibody-based enzyme-linked immunosorbent assay for detection of ustiloxin A in rice false smut balls and rice samples.

Ustiloxin A, a cyclopeptide mycotoxin, was isolated from the pathogenic fungus Villosiclava virens that causes rice false smut, a worldwide devastating rice disease. A monoclonal antibody (mAb) 2D3G5 was generated with ustiloxin A-bovine serum albumin conjugate. A highly sensitive and specific indirect competitive enzyme-linked immunosorbent assay (icELISA) was then developed. It possessed a median inhibition concentration (IC50) of 13.8 ng/mL and a working range of 2.8-72 ng/mL. The mAb 2D3G5 recognized ustiloxin B with the cross-reactivity as 4%. The average recoveries of ustiloxin A from rice false smut balls and peeled rice samples ranged from 92% to 117% and from 92% to 107%, respectively. Comparison of the concentrations of ustiloxin A in rice false smut balls detected by both icELISA and high performance liquid chromatography-photodiode array detection indicated that the developed icELISA was suitable for detection of ustiloxin A in rice food and feed samples.

Alternariol 9-methyl ether from the endophytic fungus Alternaria sp. Samif01 and its bioactivities

One bioactive compound, identified as alternariol 9-methyl ether, was isolated from the crude extract of the endophytic fungus Alternaria sp. Samif01 residing in the roots of Salvia miltiorrhiza Bunge. Alternariol 9-methyl ether was active against bacteria with minimum inhibitory concentration values ranging from 25 to 75 μg/mL and median inhibitory concentration (IC50) values ranging from 16.00 to 38.27 μg/mL. The IC50 value of alternariol 9-methyl ether against spore germination of Magnaporthe oryzae was 87.18 μg/mL. Alternariol 9-methyl ether also showed antinematodal activity against Bursaphelenchus xylophilus and Caenorhabditis elegans with IC50 values of 98.17 μg/mL and 74.62 μg/mL, respectively. This work is the first report on alternariol 9-methyl ether and its biological activities from the endophytic fungus Alternaria sp. Samif01 derived from S. miltiorrhiza Bunge. The results indicate the potential of Alternaria sp. Samif01 as a source of alternariol 9-methyl ether and also support that alternariol 9-methyl ether is a natural compound with high potential bioactivity against microorganisms.

Secondary metabolites of rice sheath blight pathogen Rhizoctonia solani Kühn and their biological activities

Abstract Eight compounds were isolated from the fermentation cultures of rice sheath blight pathogen Rhizoctonia solani Kuhn. They were identified as ergosterol (1), 6β-hydroxysitostenone (2), sitostenone (3), m-hydroxyphenylacetic acid (4), methyl m-hydroxyphenylacetate (5), m-hydroxymethylphenyl pentanoate (6), (Z)-3-methylpent-2-en-1,5-dioic acid (7) and 3-methoxyfuran-2-carboxylic acid (8) by means of physicochemical and spectroscopic analysis. Among them, 2, 3, 5–8 were isolated from R. solani for the first time. All the compounds were evaluated for their biological activities. 4–6 and 8 showed their inhibitory activities on the radical and germ elongation of rice seeds. 1, 4 and 7 showed moderate antibacterial activity to some bacteria. 4, 7 and 8 exhibited weak inhibitory activities on spore germination of Magnaporthe oryzae. 8 showed moderate antioxidant activity with the 1,1-diphenyl-2-picryhydrazyl (DPPH) and β-carotene-linoleic acid assays. This is the first time to reveal compounds 5, 6 and 8 from rice sheath blight pathogen R. solani to have in vitro phytotoxic activity.