Modification of the sporulation cycle in Penicillium digitatum (Sacc.)

Mmc, a gene involved in microcycle conidiation of the entomopathogenic fungus Metarhizium anisopliae

Microcycle conidiation is a survival mechanism for some fungi encountering unfavorable conditions, in which asexual spores germinate secondary spores directly without formation of mycelium. Here, we isolated a microcycle conidiation associated gene, Mmc, from Metarhizium anisopliae and obtained its full length of cDNA and DNA sequence. To clarify its roles in conidiation, we constructed an Mmc RNA interference (RNAi) vector with dual promoter system to knockdown Mmc transcript level, and then analyzed RNAi mutant phenotypes. On microcycle conidiation medium, the RNAi mutant performed normal conidiation instead of microcycle conidiation with significantly reduced growth speed and conidia yield of 5.29-fold and 3.18-fold lower, respectively, than that of the wild-type. Meanwhile, on normal conidiation medium, no significant difference was found in conidiation speed and total yield between the wild-type and RNAi mutant. These data demonstrated that the Mmc gene regulated microcycle conidiation but did not affect normal conidiation. In addition, results of heat treatment, UV-B radiation and bioassays of RNAi mutant indicated that Mmc was also involved in heat resistance but irrelevant to UV-B tolerance and virulence of M. anisopliae. This study helped understanding the regulation of sporulation of the entomopathogenic fungus M. anisopliae.

Sporulation of Penicillium camemberti in submerged batch culture

Sporulation of Penicillium camemberti was studied in submerged batch fermentation. A defined medium was used with glucose and ammonium as C- and N-sources. Temperature was set to 25 degrees C at pH 5.6. Essential for submerged sporulation was the presence of calcium (14 mM) which was adsorbed to the cell walls in all sporulating strains and inhibited mycelial growth. Acetate led to highly branched conidiophores and was the second main factor for efficient sporulation. The chelating properties of citrate were necessary for keeping calcium and phosphate in solution. Fermentation conditions allowed high spore yields after 96 h (1.6 x 10(8) spores/ml). Cyclopiazonic acid, the mycotoxin common for P. camemberti was produced during fermentation. The levels observed (0.5-4 ppm at 96 h) were strain specific and not related to spore yield.

Microcycle sporulation in the Claviceps purpurea 244

The mutant strain Claviceps purpurea 244 forming hyphae composed mainly from sclerotium-like cells was found to sporulate both in liquid and solid media, particularly in the form of terminal chlamydospores (4.0 x 6.5 micrometer). Chlamydospores produced during submerged cultivation germinated, new chlamydospores being formed directly from germ tubes, or, occasionally, conidia (the so-called microcycle) or new vegetative mycelium were formed. The ultrastructures of the chlamydospores and vegetative cells was identical. The cytoplasm was filled with ribosomes and contained lipid inclusions and vacuoles with membrane invaginations. Strain 244 cultivated under submerged conditions produced 150 microgram/ml clavins, with elymoclavin predominating (82%). The parent strain Claviceps pururea 129 only produced chlamydospores on the vegetative mycelium, whereas no microcycle was detected; under submerged conditions it produced mainly agroclavin (85%) at a concentration of 4 mg/ml.

Production of alkaloids and differentiation in a submerged culture of Claviceps purpurea (Fr.) Tul

The submerged culture of the Claviceps purpurea strain studied was polymorphous. In the process of alkaloid synthesis, cytodifferentiation preceded biochemical differentiation. The onset of the alkaloid phase was characterized by: predominance of chlamydospores in the culture, the presence of vegetative cells with reduced or arrested proliferation, maximum acetylCoA carboxylase activity, the maximum amount of total fatty acids, an over-average cell pool tryptophan level and minimum tryptophan synthetase activity. Intracellular ricinoleic acid was an indicator of differentiation of the culture towards alkaloid formation and also of alkaloid synthesis. The cytodifferentiation period in the initial phases of fermentation, when the cell has several alternative possibilities of development, is regarded as the most sensitive sector of the regulatory mechanisms of alkaloid formation.