Several Metarhizium Species Produce Ergot Alkaloids in a Condition-Specific Manner

Abstract

Genomic sequence data indicate that certain fungi in the genus Metarhizium have the capacity to produce lysergic acid-derived ergot alkaloids, but accumulation of ergot alkaloids in these fungi has not been demonstrated previously. We assayed several Metarhizium species grown under different conditions for accumulation of ergot alkaloids. Isolates of M. brunneum and M. anisopliae accumulated the lysergic acid amides lysergic acid α-hydroxyethyl amide, ergine, and ergonovine on sucrose-yeast extract agar but not on two other tested media. Isolates of six other Metarhizium species did not accumulate ergot alkaloids on sucrose-yeast extract agar. Conidia of M. brunneum lacked detectable ergot alkaloids, and mycelia of this fungus secreted over 80% of their ergot alkaloid yield into the culture medium. Isolates of M. brunneum, M. flavoviride, M. robertsii, M. acridum, and M. anisopliae produced high concentrations of ergot alkaloids in infected larvae of the model insect Galleria mellonella, but larvae infected with M. pingshaense, M. album, M. majus, and M. guizhouense lacked detectable ergot alkaloids. Alkaloid concentrations were significantly higher when insects were alive (as opposed to killed by freezing or gas) at the time of inoculation with M. brunneum Roots of corn and beans were inoculated with M. brunneum or M. flavoviride and global metabolomic analyses indicated that the inoculated roots were colonized, though no ergot alkaloids were detected. The data demonstrate that several Metarhizium species produce ergot alkaloids of the lysergic acid amide class and that production of ergot alkaloids is tightly regulated and associated with insect colonization.IMPORTANCE Our discovery of ergot alkaloids in fungi of the genus Metarhizium has agricultural and pharmaceutical implications. Ergot alkaloids produced by other fungi in the family Clavicipitaceae accumulate in forage grasses or grain crops; in this context they are considered toxins, though their presence also may deter or kill insect pests. Our data report ergot alkaloids in Metarhizium species and indicate a close association of ergot alkaloid accumulation with insect colonization. The lack of accumulation of alkaloids in spores of the fungi and in plants colonized by the fungi affirms the safety of using Metarhizium species as biocontrol agents. Ergot alkaloids produced by other fungi have been exploited to produce powerful pharmaceuticals. The class of ergot alkaloids discovered in Metarhizium species (lysergic acid amides) and their secretion into the growth medium make Metarhizium species a potential platform for future studies on ergot alkaloid synthesis and modification.

Keywords: Metarhizium; alkaloid secretion; biocontrol agents; ergot alkaloids; lysergic acid.