Abstract
Ergot alkaloids have an established place in plant pathology and toxicology. As pharmaceuticals, their sourcing is via natural or managed agricultural occurrence of sclerotia of Claviceps purpurea (Fr.) Tul. or through industrial fermentation processes with other Claviceps. The key factor for biosynthesis is differentiation of a particular mycelial anatomy. Previous study of these fungi from two disparate English grass genera, Spartina and Phragmites, has shown that only mycelia expressing a plectenchymatic sclerotium-like anatomy in specific axenic culture conditions elaborated ergot alkaloids, and then only as far as lysergic acid. The present report describes sequential cycles of axenic and parasitic cultivation for wild isolates from Dactylis and Alopecurus with intervention of a single ascospore step. This confirms the homozygous character of C. purpurea and defines several potential experimental axenic and parasitic conditions within the species for comparing genomic aspects of partial or full biosynthesis of cyclic tri-peptide alkaloids. Whereas Alopecurus ergot isolates readily parasitized rye, use of Dactylis isolates as inoculum for rye ovaries failed to cause the usual sphacelial fructification but supported growth of exceptionally thin sclerotia, sometimes two in a floret, with low alkaloid content attributed to reduced medullary component. However, after two cycles of axenic and rye-parasitic cultivation, and consistent re-selection of the plectenchymatic character in axenic mycelia, typical growth of ergot sclerotia occurred on rye. Caution thus seems necessary in tests for putative host specificity in any taxonomic realignments within the classical concept of C. purpurea. A Dactylis ergot isolate was also uniquely shown to parasitise the plumule of germinating rye seeds confirming the susceptibility of apical tissues. A key biosynthetic feature of a mycelial glyceride oil, rich in ricinoleic acid, as a prelude to axenic and parasitic formation of ergot alkaloids by C. purpurea is emphasised.
Highlights
The long history of ergot as a cereal and grass parasite, adversely affecting humans and agricultural ruminants, gradually evolved to include beneficial pharmaceuticals for which specific cultivation on rye on an industrial scale in Central Europe was supplemented by sclerotia salvaged via cereal seed cleaning
The advent of industrial fungal fermentations offered a challenge to mimic the biosynthesis of ergot alkaloids, previously the preserve of parasitic sclerotia
The objective was to assess the resilience of sclerotium-like differentiation aided by morphological selection across the two cultural modes, while including single ascospore selection, to establish axenic potential for the study of alkaloid biosynthesis in C. purpurea
Summary
The long history of ergot as a cereal and grass parasite, adversely affecting humans and agricultural ruminants, gradually evolved to include beneficial pharmaceuticals for which specific cultivation on rye on an industrial scale in Central Europe (e.g., in Germany, Czechoslovakia, and Switzerland) was supplemented by sclerotia salvaged via cereal seed cleaning. Biology 2020, 9, 41 axenic culture fermentation for ergot alkaloids, by an Italian isolate of Claviceps paspali, produced a simple derivative of lysergic acid [2] that became an industrial process. This was followed by Tonolo in the same Rome laboratory by the selection of a C. purpurea isolate, collected in Spain from the wheat/rye hybrid Triticale. The term reflected its compact composition in which cells of component hyphae gradually lose evidence of their filamentous origin, as is evident in longitudinal sections of developing ergot sclerotia This tissue was characterised by conforming to the natural anatomy of C. purpurea (ergot) sclerotia by their prominent glyceride oils having the hydroxy-fatty acid ricinoleic acid as the principal fatty acid in an estolide conformation [10]. The objective was to assess the resilience of sclerotium-like differentiation aided by morphological selection across the two cultural modes, while including single ascospore selection, to establish axenic potential for the study of alkaloid biosynthesis in C. purpurea
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