Comparing lignocellulose physiochemistry after decomposition by brown rot fungi with distinct evolutionary origins

Abstract

Among wood-degrading fungi, lineages holding taxa that selectively metabolize carbohydrates without significant lignin removal (brown rot) are polyphyletic, having evolved multiple times from lignin-removing white rot fungi. Given the qualitative nature of the 'brown rot' classifier, we aimed to quantify and compare the temporal sequence of carbohydrate removal among brown rot clades. Lignocellulose deconstruction was compared among fungi using distinct plant substrates (angiosperm, conifer, grass). Specifically, aspen, pine and corn stalk were harvested over a 16-week time series from microcosms containing Gloeophyllum trabeum, Fomitopsis pinicola, Ossicaulis lignatilis, Fistulina hepatica, Serpula lacrymans, Wolfiporia cocos or Dacryopinax sp. After quantifying plant mass loss, a thorough compositional analysis was complemented by a saccharification test to determine wood cell wall accessibility. Mass loss and accessibility varied depending on fungal decomposer and substrate, and trajectories of loss for hemicellulosic components and cellulose differed among plant tissue types. At any given stage of decomposition, however, lignocellulose accessibility and the fraction remaining of carbohydrates and lignin within a plant tissue type were generally the same, regardless of fungal isolate. This suggests that the sequence of plant component removal at this typical scale of characterization is shared among these brown rot lineages, despite their diverse genomes and secretomes.

Modification of the nanostructure of lignocellulose cell walls via a non-enzymatic lignocellulose deconstruction system in brown rot wood-decay fungi

“…To permit separation of cellulose elementary fibrils and aggregation of lignin, other components of the wood must be removed or modified. Although both cellulose and hemicellulose are depolymerized in early decay stages, hemicelluloses are preferentially metabolized in the first 2–4 weeks when exposed to G. trabeum, and these changes have been reported to account for 20–40% of total mass reduction during this stage [62–64]. Concurrent with depolymerization of lignin, these monomers also undergo biochemical modification, such as propyl side-chain cleavage and demethylation [5, 11–13, 65] prior to repolymerization.…”

Localizing gene regulation reveals a staggered wood decay mechanism for the brown rot fungus Postia placenta

“…S2). This brief window of differential gene regulation has been missed in earlier studies of brown rot that used homogenized whole-wood specimens, likely because that approach inevitably mixes hyphae acting asynchronously at different stages of biodegradation (7,9,21,26,29).…”

“…These oxidants apparently modify the lignocellulose to make it more susceptible to enzymatic saccharification by the limited set of GHs that brown rot fungi have retained in their genomes (13)(14)(15)(16)(17)(18). In agreement, modifications in the lignin of brown-rotted wood indicate that limited oxidative cleavage of the polymer has occurred (19)(20)(21).…”

Tamm Review: Sequestration of carbon from coarse woody debris in forest soils

“…However, this classification is not always reflected in observed differences in decomposition products . The ability to degrade specific compounds may be more accurately represented by a continuum between white-rot and brown-rot species, with many different decay mechanisms contributing to wood decay Kaffenberger and Schilling, 2015;Riley et al, 2014). Especially in angiosperms brown-rots can degrade considerable amounts of lignin .…”