Conidiogenesis and secondary metabolism in Penicillium urticae

Submerged cultures of Penicillium urticae (NRRL 2159A) produced the antibiotics patulin and griseofulvin when grown in a glucose-nitrate medium. A high concentration of calcium (i.e., 68 mM) inhibited the production of both antibiotics while stimulating conidiogenesis. Conidial mutants that were defective in an early stage of conidiogenesis produced markedly less patulin, even under growth conditions that favored secondary metabolism. A mutant which lacked the ability to produce the patulin pathway metabolites m-cresol, toluquinol, m-hydroxybenzyl-alcohol, m-hydroxybenzaldehyde, gentisaldehyde, gentisyl alcohol, gentisic acid and patulin, as well as the pathway enzyme m-hydroxybenzyl-alcohol dehydrogenase, still produced yields of conidia that were equivalent to or greater than those of the parent strain. Other mutants which were blocked at later steps of the patulin pathway also produced conidia. These results indicate that patulin and the other related secondary metabolites noted above are not a prerequisite to conidiogenesis in P. urticae. Environmental and developmental factors such as calcium levels and conidiogenesis do, however, indirectly affect the production of patulin pathway metabolites.