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Hyphal growth of Penicillium rubens in changing relative humidity
Philip Ruijten1, Hendrik P Huinink2, Olaf C G Adan1,3
1Department of Applied Physics, Eindhoven University of Technology, 5612, AZ, Eindhoven, The Netherlands.
Abstract:
When considering mold prevention strategies, the environmental conditions in which fungi grow need to be taken into consideration. This environment is often characterized by a time-dependent relative humidity, and porous substrate. Growth has mainly been investigated in steady-state experiments. Therefore, the goal of this study is to understand the hyphal growth of Penicillium rubens on porous gypsum, under dynamic humidity conditions. Spores of P. rubens were inoculated on porous gypsum containing nutrients, and placed in a small incubation chamber, allowing for microscopic hyphal observation. The relative humidity in this chamber varied multiple times between a high (close to 100%) and low value (35%, 55%, or 75%). The hyphae reacted to a lowered relative humidity by an immediate growth stop and dehydration. When the relative humidity was increased again, the hyphae re-hydrated and three responses were found: regrowing after approximately 4 h, after a time equal to the germination time, or no regrowth at all. No substantial regrowth was found for fluctuations faster than 4 h. This time-scale was found for multiple decreases in relative humidity, and has been reported for the first time. KEY POINTS: • Hyphae restart growth after a characteristic time of approximately 4 h. • Relative humidity fluctuations of 3 h can suppress hyphal growth. • Hyphae do not regrow after a severe desiccation and short periods of high humidity.
Insights
Fungal hyphae stop growing and dehydrate when relative humidity drops. They may regrow after about 4 hours when humidity increases, but rapid fluctuations can prevent regrowth entirely.
Area of Science:
- Mycology
- Environmental Microbiology
- Material Science
Background:
- Fungal growth, crucial for mold prevention, is influenced by environmental factors like relative humidity and porous substrates.
- Previous studies primarily focused on steady-state conditions, limiting understanding of fungal responses to dynamic environments.
Purpose of the Study:
- To investigate the hyphal growth dynamics of Penicillium rubens on porous gypsum under fluctuating relative humidity conditions.
- To determine the critical time scales for hyphal response and regrowth following humidity changes.
Main Methods:
- Microscopic observation of Penicillium rubens hyphae on nutrient-rich gypsum substrates within a controlled incubation chamber.
- Dynamic manipulation of relative humidity, cycling between high (near 100%) and low values (35%, 55%, or 75%).
Main Results:
- Hyphae exhibited immediate growth cessation and dehydration upon a decrease in relative humidity.
- Upon humidity increase, hyphae rehydrated and showed varied regrowth responses: immediate, after approximately 4 hours, or no regrowth.
- Fluctuations in relative humidity occurring faster than 4 hours significantly inhibited substantial hyphal regrowth.
Conclusions:
- A characteristic time of approximately 4 hours is identified for hyphal regrowth after humidity increases.
- Rapid relative humidity fluctuations, particularly those shorter than 4 hours, can effectively suppress fungal growth.
- Severe desiccation followed by brief periods of high humidity can lead to irreversible growth inhibition in hyphae.
