A new compound from an endophytic fungus Alternaria tenuissima

Diversity, antibacterial and phytotoxic activities of culturable endophytic fungi from Pinellia pedatisecta and Pinellia ternata

BACKGROUND

Endophytic fungi of medicinal plants, as special microorganisms, are important sources of antibacterial compounds. However, the diversity and antibacterial activity of endophytic fungi from Pinellia Tenore have not been systematically studied.

RESULTS

A total of 77 fungi were isolated from roots, stems, leaves, and tubers of Pinellia ternata and P. pedatisecta. All fungi were belonged to five classes and twenty-five different genera. Biological activities tests indicated that 21 extracts of endophytic fungi exhibited antibacterial activities against at least one of the tested bacteria, and 22 fermentation broth of endophytic fungi showed strong phytotoxic activity against Echinochloa crusgalli with the inhibition rate of 100%. Furthermore, four compounds, including alternariol monomethyl ether (1), alternariol (2), dehydroaltenusin (3) and altertoxin II (4), and three compounds, including terreic acid (5), terremutin (6), citrinin (7), were isolated from Alternaria angustiovoidea PT09 of P. ternata and Aspergillus floccosus PP39 of P. pedatisecta, respectively. Compound 5 exhibited strong antibacterial activities against Escherichia coli, Micrococcus tetragenus, Staphylococcus aureus, and Pseudomonas syringae pv. actinidiae with the inhibition zone diameter (IZD) of 36.0, 31.0, 33.7, 40.2 mm and minimum inhibitory concentration (MIC) values of 1.56, 3.13, 1.56, 1.56 μg/mL respectively, which were better than or equal to those of positive gentamicin sulfate. The metabolite 7 also exhibited strong antibacterial activity against P. syringae pv. actinidiae with the IZD of 26.0 mm and MIC value of 6.25 μg/mL. In addition, the compound 7 had potent phytotoxic activity against E. crusgalli with the inhibition rate of 73.4% at the concentration of 100 μg/mL.

CONCLUSIONS

Hence, this study showed that endophytic fungi of P. ternata and P. pedatisecta held promise for the development of new antibiotic and herbicide resources.

Naturally Occurring Partially Reduced Perylenequinones from Fungi

This Review provides a critical analysis of the literature covering the naturally occurring partially reduced perylenequinones (PQs) from fungi without carbon substituents (which can be named class A perylenequinones) and discusses their structures, stereochemistry, biosynthesis, and biological activities as appropriate. Perylenequinones are natural pigments with a perylene skeleton produced by certain fungi, aphids, some plants, and animal species. These compounds display several biological activities, e.g., antimicrobial, anti-HIV, photosensitizers, cytotoxic, and phytotoxic. It describes 36 fungal PQs and cites 81 references, covering from 1956 to August 2022.

Diverse polyketides from the marine endophytic Alternaria sp. LV52: Structure determination and cytotoxic activities

We report the isolation and characterization of five polyketides [alternariol (1), alternariol-9-methyl ether (2), altertoxin I (3), altertoxin II (4) and tenuazonic acid (5)] from the marine endophytic Alternaria sp. LV52 derived from Cystoseira tamariscifolia, collected from the Red Sea at Nabq-Bay, Egypt. The chemical structures of compounds 1-5 were identified by extensive 1D, 2D NMR, and HR mass measurements. Isolation and phenotypic and genotypic characterization of the producing fungus is reported. The antimicrobial activity of the produced extract and derived compounds was examined against a panel of test organisms. In addition, an in vitro cytotoxic activity of 1-5 was performed against diverse cancer cell lines: HEPG2, HELA, A549 and PC3, revealing that compounds 2 and 4 are potentially cytotoxic against A549 and PC3 with EC50 of 0.73 µg/ml (2.69 µM) and 0.17 µg/ml (0.64 µM) for 2, and 0.40 µg/ml (1.15 µM) and 0.12 µg/ml (0.33 µM) for 4, respectively.

Recent Advances in Alternaria Phytotoxins: A Review of Their Occurrence, Structure, Bioactivity and Biosynthesis

Alternaria is a ubiquitous fungal genus in many ecosystems, consisting of species and strains that can be saprophytic, endophytic, or pathogenic to plants or animals, including humans. Alternaria species can produce a variety of secondary metabolites (SMs), especially low molecular weight toxins. Based on the characteristics of host plant susceptibility or resistance to the toxin, Alternaria phytotoxins are classified into host-selective toxins (HSTs) and non-host-selective toxins (NHSTs). These Alternaria toxins exhibit a variety of biological activities such as phytotoxic, cytotoxic, and antimicrobial properties. Generally, HSTs are toxic to host plants and can cause severe economic losses. Some NHSTs such as alternariol, altenariol methyl-ether, and altertoxins also show high cytotoxic and mutagenic activities in the exposed human or other vertebrate species. Thus, Alternaria toxins are meaningful for drug and pesticide development. For example, AAL-toxin, maculosin, tentoxin, and tenuazonic acid have potential to be developed as bioherbicides due to their excellent herbicidal activity. Like altersolanol A, bostrycin, and brefeldin A, they exhibit anticancer activity, and ATX V shows high activity to inhibit the HIV-1 virus. This review focuses on the classification, chemical structure, occurrence, bioactivity, and biosynthesis of the major Alternaria phytotoxins, including 30 HSTs and 50 NHSTs discovered to date.

Chemotaxonomy of Mycotoxigenic Small-Spored Alternaria Fungi - Do Multitoxin Mixtures Act as an Indicator for Species Differentiation?

Necrotrophic as well as saprophytic small-spored Alternaria (A.) species are annually responsible for major losses of agricultural products, such as cereal crops, associated with the contamination of food and feedstuff with potential health-endangering Alternaria toxins. Knowledge of the metabolic capabilities of different species-groups to form mycotoxins is of importance for a reliable risk assessment. 93 Alternaria strains belonging to the four species groups Alternaria tenuissima, A. arborescens, A. alternata, and A. infectoria were isolated from winter wheat kernels harvested from fields in Germany and Russia and incubated under equal conditions. Chemical analysis by means of an HPLC-MS/MS multi-Alternaria-toxin-method showed that 95% of all strains were able to form at least one of the targeted 17 non-host specific Alternaria toxins. Simultaneous production of up to 15 (modified) Alternaria toxins by members of the A. tenuissima, A. arborescens, A. alternata species-groups and up to seven toxins by A. infectoria strains was demonstrated. Overall tenuazonic acid was the most extensively formed mycotoxin followed by alternariol and alternariol mono methylether, whereas altertoxin I was the most frequently detected toxin. Sulfoconjugated modifications of alternariol, alternariol mono methylether, altenuisol and altenuene were frequently determined. Unknown perylene quinone derivatives were additionally detected. Strains of the species-group A. infectoria could be segregated from strains of the other three species-groups due to significantly lower toxin levels and the specific production of infectopyrone. Apart from infectopyrone, alterperylenol was also frequently produced by 95% of the A. infectoria strains. Neither by the concentration nor by the composition of the targeted Alternaria toxins a differentiation between the species-groups A. alternata, A. tenuissima and A. arborescens was possible.

Altertoxins with potent anti-HIV activity from Alternaria tenuissima QUE1Se, a fungal endophyte of Quercus emoryi

Screening of a small library of natural product extracts derived from endophytic fungi of the Sonoran desert plants in a cell-based anti-HIV assay involving T-cells infected with the HIV-1 virus identified the EtOAc extract of a fermentation broth of Alternaria tenuissima QUE1Se inhabiting the stem tissue of Quercus emoryi as a promising candidate for further investigation. Bioactivity-guided fractionation of this extract led to the isolation and identification of two new metabolites, altertoxins V (1) and VI (2) together with the known compounds, altertoxins I (3), II (4), and III (5). The structures of 1 and 2 were determined by detailed spectroscopic analysis and those of 3-5 were established by comparison with reported data. When tested in our cell-based assay at concentrations insignificantly toxic to T-cells, altertoxins V (1), I (3), II (4), and III (5) completely inhibited replication of the HIV-1 virus at concentrations of 0.50, 2.20, 0.30, and 1.50 μM, respectively. Our findings suggest that the epoxyperylene structural scaffold in altertoxins may be manipulated to produce potent anti-HIV therapeutics.