Physiological function of hydrophobin Vmh3 in lignin degradation by white-rot fungus Pleurotus ostreatus

Hydrophobins are small-secreted proteins comprising both hydrophobic and hydrophilic parts, that can self-assemble into an amphiphilic film at the air-liquid interface. More than 20 hydrophobin genes have been estimated in the white-rot fungus Pleurotus ostreatus. In our previous studies, three hydrophobin genes were shown to be predominantly expressed under ligninolytic conditions, and only vmh3 was downregulated in both the delignification-deficient mutant Delta gat1 and Delta hir1 strains. Here, we focused on the function of the hydrophobin Vmh3 to clarify its physiological role in lignin degradation. When the hyphae were observed by transmission electron microscopy, deletion of vmh3 resulted in the disappearance of black aggregates at the interface between the cell wall and outer environment. Deletion of vmh3 resulted in reduced hydrophobicity when 0.2% sodium dodecyl sulfate was dropped onto the mycelial surface. These results suggest that Vmh3 functions on the cell surface and plays a major role in mycelial hydrophobization. Furthermore, the Delta vmh3 strain showed a marked delay in lignin degradation on beech wood sawdust medium, while the production of lignin-modifying enzymes was not reduced. This study demonstrated, for the first time, the possible effect of hydrophobin on lignin degradation by a white-rot fungus.

Automated summary

Hydrophobins are small-secreted proteins with hydrophobic and hydrophilic parts that can form amphiphilic films at the air-liquid interface. In the white-rot fungus Pleurotus ostreatus, more than 20 hydrophobin genes have been identified. Previous studies have shown that three hydrophobin genes are mainly expressed under ligninolytic conditions, and the vmh3 gene is downregulated in delignification-deficient mutant strains. This study focuses on the function of hydrophobin Vmh3 and demonstrates its role in lignin degradation.