Temporal Alterations in the Secretome of the Selective Ligninolytic Fungus Ceriporiopsis subvermispora during Growth on Aspen Wood Reveal This Organism's Strategy for Degrading Lignocellulose

Abstract

bThe white-rot basidiomycetes efficiently degrade all wood cell wall polymers. Generally, these fungi simultaneously degrade cellulose and lignin, but certain organisms, such as Ceriporiopsis subvermispora, selectively remove lignin in advance of cellulose degradation. However, relatively little is known about the mechanism of selective ligninolysis. To address this issue, C. subvermispora was grown in liquid medium containing ball-milled aspen, and nano-liquid chromatography-tandem mass spectrometry was used to identify and estimate extracellular protein abundance over time. Several manganese peroxidases and an aryl alcohol oxidase, both associated with lignin degradation, were identified after 3 days of incubation. A glycoside hydrolase (GH) family 51 arabinofuranosidase was also identified after 3 days but then successively decreased in later samples. Several enzymes related to cellulose and xylan degradation, such as GH10 endoxylanase, GH5_5 endoglucanase, and GH7 cellobiohydrolase, were detected after 5 days. Peptides corresponding to potential cellulose-degrading enzymes GH12, GH45, lytic polysaccharide monooxygenase, and cellobiose dehydrogenase were most abundant after 7 days. This sequential production of enzymes provides a mechanism consistent with selective ligninolysis by C. subvermispora.

WITHDRAWN: Identification of an endogenous redox partner for lytic polysaccharide monooxygenase-based oxidative cleavage of polysaccharides

“…Studies done on plausible reductant molecules led to the identification of interacting partners, such as small molecule reductants (5,6), lignin derived redox mediator, oxidoreductases or possibly a cosecreted dehydrogenase (4,13,15), photosynthetic pigments (16) etc, which might drive LPMO mediated cellulose degradation. Subsequent studies have also shown that a combination of AA9 protein and a co-secretory CDH (cellobiose dehydrogenase) could cleave pure cellulose (17). The identification of CDHs as redox partner for LPMO (18) was primarily dependant on (i) available secretome data which has given evidence about CDH as a LPMO co-secretory proteins and (ii) on theoretical understanding of the electron transport processes involved in LPMO activation (17,(19)(20)(21)(22).…”

“…Subsequent studies have also shown that a combination of AA9 protein and a co-secretory CDH (cellobiose dehydrogenase) could cleave pure cellulose (17). The identification of CDHs as redox partner for LPMO (18) was primarily dependant on (i) available secretome data which has given evidence about CDH as a LPMO co-secretory proteins and (ii) on theoretical understanding of the electron transport processes involved in LPMO activation (17,(19)(20)(21)(22). However, there are many filamentous fungi which do not secrete CDH (because of obvious lack of encoding gene) and in contrast many ascomycetes are known to encode multiple CDHs (20), suggesting that the choice of redox partner is very specific to type of LPMO and no general concept exist.…”

A Highly Diastereoselective Oxidant Contributes to Ligninolysis by the White Rot Basidiomycete Ceriporiopsis subvermispora

“…This process occurs in nature when certain white rot fungi delignify wood selectively, growing on its hemicelluloses before they consume the cellulose that is exposed later via delignification (1)(2)(3)(4). In part, timing of gene expression underlies this strategy, with the one-electron oxidative systems that depolymerize lignin via free radical intermediates being expressed before cellulases (5). However, temporal regulation alone cannot explain the observed selectivity, because some fungal ligninolytic oxidants are nonselective reactive oxygen species (e.g., Fenton reagent) that attack cellulose as well as lignin (6); that is, the cellulose will be depolymerized if the ligninolytic oxidants deployed before cellulases are of this nonspecific type, whereas selective delignification will occur instead if the oxidants specifically target the lignin.…”

“…However, C. subvermispora has never been found to produce LiP or versatile peroxidase, the selective ligninolytic oxidants that are currently known from fungi, nor has it been found to secrete small aromatic redox mediators, such as veratryl alcohol, that might work in conjunction with these enzymes to infiltrate and delignify the wood cell wall (5,20). On the other hand, C. subvermispora carries two genes that were previously shown via heterologous expression to encode enzymes with LiP activity (21,22).…”

High value‐added monomer chemicals and functional bio‐based materials derived from polymeric components of lignocellulose by organosolv fractionation

“…Typically, white‐rot fungi, Phanerochaete chrysosporium , can produce numerous types of oxidoreductases, so it shows a strong ability to depolymerize lignin effectively from natural biomass fibers . Phanerochaete chrysosporium can simultaneously metabolize lignin and cellulose / hemicelluloses . Ceriporiopsis subvermispora has the ability to convert lignin selectively in advance of cellulose degradation .…”