Conidiation of Penicillium camemberti in submerged liquid cultures is dependent on the nitrogen source.

Objective: To study the ability of a commercial Penicillium camemberti strain, used for Camembert type cheese ripening, to produce conidia during growth in liquid culture (LC), in media containing different sources of nitrogen as, industrially, conidia are produced by growth at the surface of a solid state culture because conidiation in stirred submerged aerobic LC is not known.

Results: In complex media containing peptic digest of meat, hyphae ends did not differentiate into phialides and conidia. Contrarily, in a synthetic media containing KNO3 as sole nitrogen source, hyphae ends differentiated into phialides producing 0.

Production of conidia of Penicillium camemberti in liquid medium through microcycles of conidiation.

Microcycle conidiation is a survival mechanism of fungi encountering unfavorable conditions. In this phenomenon, asexual spores germinate secondary spores directly without formation of mycelium. As Penicillium camemberti conidia have the ability to produce conidiophores after germination in liquid culture induced by a thermal stress (18 and 30 °C), our work has aimed at producing conidia through this mean.

Cloning and expression of genes involved in conidiation and surface properties of Penicillium camemberti grown in liquid and solid cultures.

Based on bioinformatic data on model fungi, the rodA and wetA genes encoding, respectively, a RodA hydrophobin protein and the WetA protein involved in conidiation mechanisms, were PCR-cloned and characterized for the first time in Penicillium camemberti. These results, completed by a sequence of the brlA gene (available in GenBank), which encodes a major transcriptional regulator also involved in the conidiation mechanism, were used to compare, by qRT-PCR, the expression of the three genes in liquid and solid cultures in a synthetic medium. While expression of the brlA and wetA genes increased dramatically in both culture conditions after 4 days of growth, expression of the rodA gene increased only with conidiation and in the solid culture, and this expression was correlated with production and secretion of a RodA protein outside the hyphae, which became very hydrophobic.