Relationship between the morphology of Claviceps purpurea and the production of alkaloids

Comparative Ergot Alkaloid Elaboration by Selected Plectenchymatic Mycelia of Claviceps purpurea through Sequential Cycles of Axenic Culture and Plant Parasitism

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.

Purpurolic acid: A new natural alkaloid from Claviceps purpurea (Fr.) Tul

A novel secondary metabolite from the sclerotia of Claviceps purpurea (Fr.) Tul. is described; the structure is based on (1)H and (13)C NMR spectroscopy and electrospray mass spectrometry. It has an elemental composition C10H16N2O7 and is comprised mainly of proline and alanine moieties, although without peptide linkage. Notably, these amino-acids are also components of the cyclic tripeptide side chain of several classic ergoline alkaloids. Designated as purpurolic acid, the new compound is the principal free amino-acid in ergot and its natural abundance exceeds that of the ergoline alkaloids with which it accumulates in parallel during parasitic development. In contrast, it does not accumulate in the fungus in axenic culture, even when ergotamine is synthesised. The extent to which the compound is a metabolite of other ergot fungi worldwide is unknown. Biological activity and metabolic significance also remain unknown, but purpurolic acid could become a biomarker for detection of ergot contamination in agricultural products of temperate latitudes.

Alkaloid production by isolates of the sorghum ergot pathogen (Claviceps africana) from Australia and other countries

Isolates of Claviceps africana from Australia, Africa, Asia, and America were tested for the production of dihydroergosine (DHES), and its biogenic precursors dihydroelymoclavine (DHEL) and festuclavine (FEST), in culture. Several growth media were evaluated to optimise alkaloid production with little success. The best of these involved 2-stage culturing on high-sucrose substrate. Australian C. africana isolates varied widely and inconsistently in alkaloid production, with DHES concentrations in mycelium ranging from: <0.1 to 9 mg DHES/kg; <0.1 to 1.6 mg DHEL/kg; and <0.1 to 0.4 mg FEST/kg. In a separate experiment using similar culturing techniques, DHES was produced by 2 of 3 Australian isolates, 1 of 3 USA isolates, 1 of 4 Indian isolates, the sole Puerto Rican isolate, the sole Japanese isolate, but not the sole South African isolate. In this experiment, DHES concentrations detected in mycelium of Australian isolates (0.1–1.0 mg DHES/kg) were of similar magnitude to isolates from other countries (0.2–1.8 mg DHES/kg). Three C. africana isolates, including one that produced only traces of alkaloid in culture after 8 weeks, were inoculated onto panicles of sterile male sorghum plants. After 8 weeks, all 3 isolates produced 10–19 mg DHES/kg in the panicles, demonstrating that the growing plant favoured more consistent alkaloid production than culture medium.

Changes in cytoplasmic ultrastructure during submerged cultivation of a peptide alkaloids-producing strain of Claviceps purpurea (Fr.) Tul

A strain of Claviceps purpurea, designated Pepty 695/S produces ergotoxine alkaloids under particular conditions of fermentation. The onset of alkaloid synthesis occurs around the second day of cultivation. Alkaloid formation is connected with morphological and ultrastructural changes. In the first 3-5 days of cultivation short thickened, septated hyphae, organized in plectenchymatic pellets as well as large single cells are formed. The hyphae are ultrastructurally characterized by increasing number of lipid droplets, deposits of glycogen and by extended ER membranes, which apparently may form numerous vesicles. The correlations between lipid and alkaloid synthesis are discussed.

Origin of sclerotia-like cells in submerged Claviceps purpurea producing clavine alkaloids

Ultrathin sectioning of submerged mycelium of Claviceps purpurea Tul. producing clavine alkaloids revealed yeast-like budding resulting in asexual spores-blastospores. These deciduous spores were born by extended hyphal cells and retained the same ultrastructure of cell organelles. Both the extended hyphae and the blastospores resembled the cells of ergot sclerotial tissue. A surface culture of C. purpurea Tul. producing no alkaloids was used as a reference.

Morphogenesis and ultrastructure of Claviceps purpurea during submerged alkaloid formation

Criteria for morphogenetic and ultrastructural distinction between conidia and chlamydospores of a submerged culture of Claviceps purpurea (Fr.) Tul. are described. Both the hyphae of the sphacelia (asexual) stage and the conidia contained granular cytoplasm. Cytoplasmic invaginations in vacuoles were transformed to electron-opaque bodies and disintegrated prior to germination. The budding of conidia had basipetal succession. The chlamydospores were formed by rounding up the terminal cells of filamentous hyphae. Homogeneous nonvacuolized cytoplasm with lipid droplets and lipid-forming bodies was characteristic of young chlamydospores. Cristate mitochondria did not appear in the chlamydospores before the alkaloid production phase. Simultaneously a specific organelle in the chlamydospores, a dense body, appeared to absorb intracellular lipids and form large deposits of phospholipid material. No germination of chlamydospores was observed. The ultrastructural pattern described for chlamydospores was also observed in hyphae with reduced proliferation during the alkaloid production phase.