Temperature, water activity and pH during conidia production affect the physiological state and germination time of Penicillium species

• Published in: International journal of food microbiology Vol. 241; pp. 151 - 160
• Main Authors: Nguyen Van Long, Nicolas, Vasseur, Valérie, Coroller, Louis, Dantigny, Philippe, Le Panse, Sophie, Weill, Amélie, Mounier, Jérôme, Rigalma, Karim
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 16-01-2017; Elsevier BV; Elsevier
• Subjects: Cold Temperature; Compatible solutes; Conidia; Conidial germination; Electron microscopy; Environment; Environmental conditions; Fermented food; Food contamination; Food contamination & poisoning; Food Contamination - analysis; Food spoilage; Fungi; Germination; Germination - physiology; Glucose - analysis; Hydrogen ions; Impact analysis; Life Sciences; Low temperature; Mannitol; Mannitol - analysis; Maturation; Microbiology and Parasitology; Microscopy, Electron, Transmission; Mycelia; Mycelium - growth & development; Mycology; Penicillium - growth & development; Penicillium - metabolism; Penicillium expansum; Penicillium roqueforti; pH effects; Physiology; Predictive mycology; Solutes; Spoilage; Spores, Fungal - growth & development; Sporulation; Studies; Temperature; Temperature effects; Transmission electron microscopy; Trehalose; Trehalose - analysis; Water; Water activity; Compatible solutes; Predictive mycology; Penicillium expansum; Conidial germination; Penicillium roqueforti; Sporulation
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2016.10.022

Conidial germination and mycelial growth are generally studied with conidia produced under optimal conditions to increase conidial yield. Nonetheless, the physiological state of such conidia most likely differs from those involved in spoilage of naturally contaminated food. The present study aimed at investigating the impact of temperature, pH and water activity (aw) during production of conidia on the germination parameters and compatible solutes of conidia of Penicillium roqueforti and Penicillium expansum. Low temperature (5°C) and reduced aw (0.900 aw) during sporulation significantly reduced conidial germination times whereas the pH of the sporulation medium only had a slight effect at the tested values (2.5, 8.0). Conidia of P. roqueforti produced at 5°C germinated up to 45h earlier than those produced at 20°C. Conidia of P. roqueforti and P. expansum produced at 0.900 aw germinated respectively up to 8h and 3h earlier than conidia produced at 0.980 aw. Furthermore, trehalose and mannitol assessments suggested that earlier germination might be related to delayed conidial maturation even though no ultra-structural modifications were observed by transmission electron microscopy. Taken together, these results highlight the importance of considering environmental conditions during sporulation in mycological studies. The physiological state of fungal conidia should be taken into account to design challenge tests or predictive mycology studies. This knowledge may also be of interest to improve the germination capacity of fungal cultures commonly used in fermented foods.
•A simple method to study fungal spore germination on solid medium is proposed.•Penicillium roqueforti conidia produced at 5°C germinate up to 45h earlier than conidia produced at 20°C.•P. roqueforti and P. expansum conidia produced at 0.900 aw germinate up to 8h earlier than conidia produced at 0.980 aw.•Delayed maturation is supposed to reduce the germination time as reflected by trehalose and mannitol content of conidia.•The physiological state of conidia should be considered to design challenge tests or predictive mycology studies.