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YEAST-MYCELIAL DIMORPHISM IN CERATOCYSTIS ULMI
Abstract
The nutritional parameters controlling the yeast-mycelial dimorphism in Ceratocystis ulmi, the causative agent of Dutch elm disease, have been established. The nitrogen source is critical. In a defined phosphate buffered glucose-salts liquid medium the presence of proline induces the yeast morphology whereas ammonium, arginine, or asparagine induce the mycelial state. This phenomenon is not a secondary manifestation of pH changes in the respective media and it can be achieved with either a blastospore or conidiospore inoculum. The dimorphism is, however, dependent on the inoculum size. Yeasts are only formed in the proline-containing medium, when the initial inoculum concentration is (GREATERTHEQ) 10('6) blastospores/ml. Once the blastospores produce visible buds or germ tubes they are "committed to that mode of development, in the sense that if they are now resuspended in the medium which induces the opposite morphology, at the same cell concentration, the alternate morphology can no longer be produced. The DNA synthesis in blastospores, commences concomitantly with bud initiation or germ tube initiation, and is required for development and commitment, as hydroxyurea which inhibits DNA synthesis also inhibits development. Both RNA and protein synthesis begin within one hour after inoculation. The RNA synthesis is required for development, since RNA synthesis inhibitors and the fluoro-derivatives of uracil block development. The common eukaryotic and prokaryotic protein synthesis inhibitors were without effect in C. ulmi. Paraflouro-phenylalanine blocked the morphogenesis of blastospores when added at the time of inoculation. But when added between 3 and 10 hours after inoculation, the blastospores were inhibited in proline containing medium, whereas the spores in arginine containing medium developed in the yeast phase. The blastospores were resistant to cerulenin, whereas the conidiospores were sensitive to low levels of cerulenin. The cerulenin resistance in the former was correlated with lipid reserves, in the form of refractile inclusions which were absent in the latter. The cerulenin inhibition of conidiospores was reversed by saturated free fatty acids and tweens. Increasing the membrane fluidity of conidiospores, in proline containing medium, by an exogeneous supply of unsaturated fatty acids in the presence of cerulenin, induces germination. Furthermore, membrane synthesis is not required for phase transition. Besides dimorphism, C. ulmi exhibits a variety of morphologically distinct entities in shake cultures. In a low phosphate-glucose-ammonium-salts medium, the mycelium undergoes fragmentation in the stationary phase to yield arthrospores and chlamydospores. Chlamydospores are also formed from blastospores when ammonium chloride is added to a late log phase yeast culture. A semi-defined glucose-yeast extract medium supports the production of asexual fruiting structures called synnema. Erythromycin or inhibitory ethanol levels induce pseudohyphae in arginine-containing medium.
Subject Area
Microbiology
Recommended Citation
KULKARNI, RAJIV KRISHNA, "YEAST-MYCELIAL DIMORPHISM IN CERATOCYSTIS ULMI" (1981). ETD collection for University of Nebraska-Lincoln. AAI8118168.
https://digitalcommons.unl.edu/dissertations/AAI8118168