Differentiation of Claviceps purpurea in axenic culture

The growth form of a strain of Claviceps purpurea in axenic culture has been controlled by the amino nitrogen source. Within the pairs asparagine/aspartic acid or glutamine/glutamic acid the amide promoted sphacelial growth of the colony whereas the acid supported differentiation of plectenchymatic sclerotial tissue and synthesis of ergot alkaloids. Sclerotial colonies showed purple pigmentation. The mycelium had a greater lipid content, rich in ricinoleic acid, and sporulation was much less than in sphacelial colonies. Changes in the relative distribution of amino acids between the free and peptidyl components of the cells was most marked with respect to lysine; growth on asparagine resulted in more than half remaining free, whereas less than 10% remained free on aspartic acid. Lysine supplied exogenously as a nitrogen source did not promote sclerotial differentiation. Frequent transfers to fresh medium of colonies grown on dialysis membrane accentuated the extent of sphacelial or sclerotial growth; four transfers during an 18-day growth period yielded mycelia with an alkaloid content (0-4%, w/w) similar to that of parasitic ergot sclerotia. Asparagine and glutamine were taken up more rapidly from liquid media than their corresponding acids, but each acid exerted a dominant effect over the amide, in a mixture providing equivalent nitrogen, resulting in differentiation from sphacelial to sclerotial growth analogous to that occurring during parasitism. The apparently greater (w/w) proportion of total amino acids in sphacelial mycelia than in sclerotial mycelia mainly reflected the lower lipid content of these tissues, but this factor was insufficient to account for the persistence of a significant proportion of the total lysine amongst the free amino acids. The promotion of sclerotial growth by aspartic and glutamic acids was not confined solely to the experimental strain of the fungus. Although some isolates failed to differentiate into plectenchymatic mycelia on these nitrogen sources, the extent of their sphacelial growth, as indicated by the degree of sporulation, was always much reduced with respect to that promoted by asparagine.