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How a fungus escapes the water to grow into the air
H A Wösten1, M A van Wetter, L G Lugones
1Groningen Biomolecular Sciences, Biotechnology Institute, Laboratory of Molecular Plant Biology, Department of Microbiology, University of Groningen, Kerklaan 30 9751, NN Haren, The Netherlands. wostenha@biol rug.nl.
Abstract:
Fungi are well known to the casual observer for producing water-repelling aerial moulds and elaborate fruiting bodies such as mushrooms and polypores. Filamentous fungi colonize moist substrates (such as wood) and have to breach the water-air interface to grow into the air. Animals and plants breach this interface by mechanical force. Here, we show that a filamentous fungus such as Schizophyllum commune first has to reduce the water surface tension before its hyphae can escape the aqueous phase to form aerial structures such as aerial hyphae or fruiting bodies. The large drop in surface tension (from 72 to 24 mJ m-2) results from self-assembly of a secreted hydrophobin (SC3) into a stable amphipathic protein film at the water-air interface. Other, but not all, surface-active molecules (that is, other class I hydrophobins and streptofactin from Streptomyces tendae) can substitute for SC3 in the medium. This demonstrates that hydrophobins not only have a function at the hyphal surface but also at the medium-air interface, which explains why fungi secrete large amounts of hydrophobin into their aqueous surroundings.
Insights
Filamentous fungi reduce water surface tension using secreted hydrophobins (SC3) to enable aerial growth. This self-assembly of proteins at the water-air interface is crucial for forming structures like aerial hyphae and fruiting bodies.
Area of Science:
- Mycology
- Biochemistry
- Surface Science
Background:
- Fungi, such as Schizophyllum commune, grow on moist substrates and must overcome the water-air interface to form aerial structures.
- Plants and animals utilize mechanical force to breach this interface, but fungal mechanisms were less understood.
Purpose of the Study:
- To investigate the mechanism by which filamentous fungi breach the water-air interface for aerial growth.
- To identify the role of secreted molecules in facilitating fungal escape from aqueous environments.
Main Methods:
- Observational studies on Schizophyllum commune growth.
- Analysis of surface tension reduction in aqueous media.
- Investigation of self-assembly of secreted hydrophobins (SC3) at the water-air interface.
- Testing the efficacy of alternative surface-active molecules.
Main Results:
- Filamentous fungi must reduce water surface tension to form aerial structures.
- The secreted hydrophobin SC3 self-assembles into an amphipathic film, significantly lowering surface tension from 72 to 24 mJ m-2.
- Other class I hydrophobins and streptofactin can substitute for SC3, indicating a broader role for surface-active molecules.
Conclusions:
- Hydrophobins play a critical role not only on the hyphal surface but also at the medium-air interface for fungal aerial development.
- The secretion of large amounts of hydrophobins into the surrounding medium is essential for overcoming surface tension and enabling growth into the air.
- This mechanism explains how fungi achieve aerial colonization and form macroscopic structures.