The Known Antimammalian and Insecticidal Alkaloids Are Not Responsible for the Antifungal Activity of Epichloë Endophytes

Abstract

Asexual Epichloë sp. endophytes in association with pasture grasses produce agronomically important alkaloids (e.g., lolitrem B, epoxy-janthitrems, ergovaline, peramine, and lolines) that exhibit toxicity to grazing mammals and/or insect pests. Novel strains are primarily characterised for the presence of these compounds to ensure they are beneficial in an agronomical setting. Previous work identified endophyte strains that exhibit enhanced antifungal activity, which have the potential to improve pasture and turf quality as well as animal welfare through phytopathogen disease control. The contribution of endophyte-derived alkaloids to improving pasture and turf grass disease resistance has not been closely examined. To assess antifungal bioactivity, nine Epichloë related compounds, namely peramine hemisulfate, n-formylloline-d3, n-acetylloline hydrochloride, lolitrem B, janthitrem A, paxilline, terpendole E, terpendole C, and ergovaline, and four Claviceps purpurea ergot alkaloids, namely ergotamine, ergocornine, ergocryptine, and ergotaminine, were tested at concentrations higher than observed in planta in glasshouse and field settings using in vitro agar well diffusion assays against three common pasture and turf phytopathogens, namely Ceratobasidium sp., Drechslera sp., and Fusarium sp. Visual characterisation of bioactivity using pathogen growth area, mycelial density, and direction of growth indicated no inhibition of pathogen growth. This was confirmed by statistical analysis. The compounds responsible for antifungal bioactivity of Epichloë endophytes hence remain unknown and require further investigation.

A Metabolomic Study of Epichloë Endophytes for Screening Antifungal Metabolites

“…A second study reported that the 'known knowns'-Epichloë sp. related antimammalian and insecticidal alkaloids-are not responsible for the observed antifungal bioactivity [57].…”

“…and Fusarium sp. in agar well diffusion assays [57]. Thus, the opportunity now arises to investigate novel Epichloë sp.…”

“…Importantly, the in vitro antifungal phenotypes observed by Fernando et al, (2020) were consistent; observed in independent isolates, across duplicate assays, and under two different culture environment conditions; solid plate-based dual culture assays and agar well diffusion assays using extracts of liquid media supernatant. A second study by Fernando et al, (2021) established that the known antimammalian and insecticidal alkaloids are not responsible for the antifungal activity observed in bioactive Epichloë endophyte strains [57]. However, the bioactive compounds should be discoverable using bioassayguided fractionation and isolation.…”

A First Draft of the Core Fungal Microbiome of Schedonorus arundinaceus with and without Its Fungal Mutualist Epichloë coenophiala

“…Epichloë have been found to have antifungal properties before. However, these results may be due to factors other than the alkaloids that confer many of its other effects, because Fernando et al [ 56 ] found no antifungal activity for a variety of common Epichloë -produced alkaloids on several plant pathogens.…”

Structures and Biological Activities of Alkaloids Produced by Mushrooms, a Fungal Subgroup

“…The last time a new compound of the terpendole family was discovered was in 1999, when terpendole M was isolated from the fungus Neotyphodium lolii [ 119 ]. It should be noted that during the 2002–2022 period, new studies were carried out evaluating the bioactivity of some terpendoles [ 120 , 121 , 122 , 123 , 124 , 125 , 126 ]. Three new terpendoles produced by the fungus Volutella citronella , two of them named terpendoles N and O ( 90 and 91 , Figure 6 ), were reported in another study [ 127 ], but their structures were different to those published by Zhu et al (2020) [ 55 ].…”