Abstract
The filamentous fungus Podospora anserina is a good model to study the breakdown of lignocellulose, owing to its ease of culture and genetical analysis. Here, we show that the fungus is able to use a wide range of lignocellulosic materials as food sources. Using color assays, spectroscopy and pyrolysis–gas chromatography mass spectrometry, we confirm that this ascomycete is able to degrade lignin, primarily by hydrolyzing β–O-4 linkages, which facilitates its nutrient uptake. We show that the limited weight loss that is promoted when attacking Miscanthus giganteus is due to a developmental blockage rather than an inefficiency of its enzymes. Finally, we show that lignin, and, more generally, phenolics, including degradation products of lignin, greatly stimulate the growth and fertility of the fungus in liquid cultures. Analyses of the CATΔΔΔΔΔ mutant lacking all its catalases, pro-oxidants and antioxidants indicate that improved growth and fertility of the fungus is likely caused by augmented reactive oxygen species levels triggered by the presence of phenolics.
Highlights
Lignocellulose breakdown by fungi is a complex and incompletely known process requiring a combination of enzymatic [1,2] and non-enzymatic reactions [3], whose ratios depend on the fungal species
A succession of fungal species fructifies on dung, and P. anserina is among the fungi that fructify late in the succession, suggesting that it is able to scavenge energy from hard-to-digest materials such as the plant cell wall, which cannot be consumed by earlier fructifying species
These variations are likely related to the plant consumed by the herbivores, as they may contain different types of lignocelluloses and/or toxic chemicals of natural or anthropogenic origin
Summary
Lignocellulose breakdown by fungi is a complex and incompletely known process requiring a combination of enzymatic [1,2] and non-enzymatic reactions [3], whose ratios depend on the fungal species. Degradation of lignin is supposed to be energy-demanding and is construed as mostly non-stereospecific, some bacterial enzymes have some stereospecific actions [8,9] It requires the action of “auxiliary activity (AA). These enzymes have various redox activities, including many generating peroxide (e.g., cellobiose dehydrogenases, glucose, other sugars and alcohol oxidases, etc.) and others using the peroxide to produce small reactive molecules (e.g., lignin peroxidases and Mn peroxidases). These small molecules interact non- with the various macromolecules present in the plant cell wall and cleave them.
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