Lignin Degradation by Ascomycetes

In nature, it is often surmised that lignin is degraded almost exclusively by basidiomycetes, with minor contributions from bacteria and even fewer from ascomycetes. Yet, numerous studies underscore the ability of many ascomycetes from a wide range of taxonomic classes to degrade newly-formed and ancient lignin, sometime more efficiently than basidiomycetes. Few genomes from ascomycetes have been analyzed in relation with their potential ability to breakdown lignin; yet, these also point out a rich repertoire of enzymes with auxiliary activities suspected to participate in lignin lysis. Not surprisingly, the molecular mechanisms used by ascomycetes to break down lignin are largely unknown. Here, we review the literature on this topic. We also present potential mechanisms by which Podospora anserina, a model ascomycete well-suited to decipher how ascomycetes breakdown lignin, may do so. Owing to their huge biomass, which dominates in soils, and despite the fact that they usually are less efficient than basidiomycetes, it is most likely that ascomycetes actually play important roles in ensuring the recycling of lignin in nature.