Antimicrobial activities of an oxygenated cyclohexanone derivative isolated from Amphirosellinia nigrospora JS-1675 against various plant pathogenic bacteria and fungi

Abstract

Aims To evaluate the antimicrobial activities of an active compound isolated from the culture broth of Amphirosellinia nigrospora JS‐1675 against various plant pathogenic bacteria and fungi. Methods and Results While screening for bioactive secondary metabolites from endophytic fungi, we found that A. nigrospora JS‐1675 showed strong in vitro antibacterial activity against Ralstonia solanacearum. One compound (1) was isolated and identified as (4S, 5S, 6S)‐5,6‐epoxy‐4‐hydroxy‐3‐methoxy‐5‐methyl‐cyclohex‐2‐en‐1‐one. Growth of most of the tested phytopathogenic bacteria was inhibited by compound 1 and the ethyl acetate (EtOAc) layer except Pseudomonas syringae pv. lachrymans. Compound 1 also inhibited the mycelial growth of several plant pathogenic fungi. Both compound 1 and the EtOAc layer reduced bacterial leaf spot disease in detached peach leaves. They also suppressed the development of bacterial wilt on tomato seedlings quite effectively. Conclusions Amphirosellinia nigrospora JS‐1675 showed antimicrobial activity against plant pathogenic bacteria and fungi by producing compound 1. Significance and Impact of the Study This is the first report on the occurrence of compound 1 in A. nigrospora JS‐1675 and its efficacy against plant pathogenic bacteria and fungi. Their strong disease control efficacy against tomato bacterial wilt suggests that this fungus can be used as a microbial bactericide.

Recent progress in biodiversity research on the Xylariales and their secondary metabolism

“…The genus Amphirosellinia was not studied for secondary metabolites until recently, when the first natural product, coriloxin (1), was discovered from cultures of Amphirosellinia nigrospora [11]. Coriloxin represents a known cyclohexenone derivative [12] and was found to have weak antimicrobial activities.…”

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“…Endophytic fungal strains were isolated, sequenced in the ribosomal region for putative identification, and stored for further study according to the procedures described in Nguyen et al (2019). Each isolate was stored at −80 • C as a glycerol stock before use, and deposited at the Wildlife Genetic Resources Bank of National Institute of Biological Resources ( Supplementary Table S3).…”

“…Each isolate was stored at −80 • C as a glycerol stock before use, and deposited at the Wildlife Genetic Resources Bank of National Institute of Biological Resources ( Supplementary Table S3). Preliminary identification of the endophytic fungi was based on cultural morphology on PDA and ITS sequences (Nguyen et al, 2019).…”

“…The antagonistic activity of endophytic fungi isolated from the plant was assessed by 96 well microtiter plate using broth dilution method against S. homoeocarpa, a fungal pathogen of dollar spot of creeping bentgrass (Nguyen et al, 2019). The mycelial fragment suspensions in sterile distilled water (50 mg fresh mycelia per ml), at 1%, were used as inocula for antifungal bioassay using PDB.…”

“…Several bioactive secondary metabolites that suppress the plant diseases have been known to be produced by fungal endophytes. An oxygenated cyclohexanone derivative ([4S, 5S, 6S]-5,6-epoxy-4-hydroxy-3-ethoxy-5-methyl-cyclohex-2-en-1-one) isolated from an endophytic fungus Amphirosellinia nigrospora showed antifungal and antibacterial activities against various plant pathogens (Nguyen et al, 2019). Several compounds isolated from fungal endophytic Phoma species also exhibited antifungal activities (Wang et al, 2012).…”