Fungal metaproteome indicates strong functional redundancy during wood decomposition of 12 different tree species

Background/Question/Methods

Wood-decaying fungi are the most efficient degraders of plant cell walls, making them key players in forest ecosystems and the global carbon cycle. Especially, deadwood is of paramount importance for forest biodiversity and function harboring far more than 1,000 fungi and more than 1,000 Coleoptera species. Changes in the variation of diversity and abundance of wood-decaying microorganisms are well studied, while knowledge of their in situ biochemical processes is scarce. To clarify the fungal lignocellulolytic enzymatic process involved in wood decomposition, metaproteomic patterns of extensively decayed logs of 12 tree species were examined. We hypothesized that the functional activity of the diverse wood decomposing fungi is redundant in the 12 deadwood tree species, whereas their taxonomic diversity is deadwood tree species-dependent.The experiment was conducted in the context of the German Biodiversity Exploratories (www.biodiversity-exploratories.de). Deadwood samples were milled, extracted and trypsin-digested peptide lysates were measured by mass spectrometry (Q Exactive HF) and compared to a user-defined database including the genome sequences of the deadwood inhabiting fungi. Spectral matches were counted and related to fungal taxonomy and function based on CAZy-related enzymes (www.cazy.org). We applied two-dimensional data visualization (heatmaps) and a non-parametric multivariate statistical test (perMANOVA) to test our hypothesis.

Results/Conclusions

The fungal taxonomic diversity varied strongly between the 12 tree species (which was also verified by a metabarcoding approach) and showed differences in functional activities depending on the fungal species. A perMANOVA analysis for fungal species showed significant differences (p < = 0.05) between the deadwood tree species, whereas the perMANOVA for enzymatic classes exhibited no differences, indicating functional redundancy. Highly abundant enzymes across the 12 deadwood tree species were: laccase, peroxidases, endoglucanases, alcohol oxidases and lytic polysaccharide monooxygenases. Our results confirm a deadwood tree species effect of the fungal diversity and abundance based on metaproteomics, but interestingly showed also the strong functional redundancy of the fungal lignocellulolytic system during wood decomposition. Metaproteomics provides a crucial step in the mechanistic understanding of microbial deadwood decomposition.