Fast solubilization of recalcitrant cellulosic biomass by the basidiomycete fungus Laetisaria arvalisinvolves successive secretion of oxidative and hydrolytic enzymes

Abstract

BackgroundEnzymatic breakdown of lignocellulosic biomass is a known bottleneck for the production of high-value molecules and biofuels from renewable sources. Filamentous fungi are the predominant natural source of enzymes acting on lignocellulose. We describe the extraordinary cellulose-deconstructing capacity of the basidiomycete Laetisaria arvalis, a soil-inhabiting fungus.ResultsThe L. arvalis strain displayed the capacity to grow on wheat straw as the sole carbon source and to fully digest cellulose filter paper. The cellulolytic activity exhibited in the secretomes of L. arvalis was up to 7.5 times higher than that of a reference Trichoderma reesei industrial strain, resulting in a significant improvement of the glucose release from steam-exploded wheat straw. Global transcriptome and secretome analyses revealed that L. arvalis produces a unique repertoire of carbohydrate-active enzymes in the fungal taxa, including a complete set of enzymes acting on cellulose. Temporal analyses of secretomes indicated that the unusual degradation efficiency of L. arvalis relies on its early response to the carbon source, and on the finely tuned sequential secretion of several lytic polysaccharide monooxygenases and hydrolytic enzymes targeting cellulose.ConclusionsThe present study illustrates the adaptation of a litter-rot fungus to the rapid breakdown of recalcitrant plant biomass. The cellulolytic capabilities of this basidiomycete fungus result from the rapid, selective and successive secretion of oxidative and hydrolytic enzymes. These enzymes expressed at critical times during biomass degradation may inspire the design of improved enzyme cocktails for the conversion of plant cell wall resources into fermentable sugars.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-014-0143-5) contains supplementary material, which is available to authorized users.

Substrate specificity and regioselectivity of fungal AA9 lytic polysaccharide monooxygenases secreted by Podospora anserina

“…A peculiarity of fungal AA9 LPMOs is the methylation of their N-terminal histidine at the imidazole Nε2 [ 18 , 27 ]. To investigate whether Pa LPMO9s harbored this unusual post-translational modification, mass spectrometry (MS) analyses on tryptic digests of Pa LPMO9E and Pa LPMO9H were performed.…”

“…Protein concentration was determined by using the Bradford assay (Bio-Rad, Marnes-la-Coquette, France). Tryptic digest of each purified recombinant protein was analyzed using MS as described in [ 27 ].…”

“…AA9 LPMOs are frequently multimodular bearing a CBM1 at their C terminus. Post-genomic analyses of saprophytic fungi have shown that AA9 LPMOs’ isoforms are specifically secreted during degradation of lignocellulosic substrates [ 22 – 27 ]. In this study, we focused on AA9 LPMOs identified in the secretome of P. anserina that was shown to significantly improve the saccharification yield of steam-exploded wheat straw [ 26 ].…”

Transcriptomic responses to warming and cooling of an Arctic tundra soil microbiome

“…They constitute the first wave of attack on the most recalcitrant natural polysaccharides and initiate degradation of lignocellulose (Johansen, 2016) and chitin (Vaaje-Kolstad et al, 2010). Thus, lytic polysaccharide monooxygenases are secreted relatively early in the degradation process, while cellulases only appear at elevated levels later in the degradation process (Navarro et al, 2014).…”

Inactivation of Cellobiose Dehydrogenases Modifies the Cellulose Degradation Mechanism of Podospora anserina

“…CDHs are secreted by a variety of fungi, including white-rot, brown-rot, and soft-rot fungi, as well as molds (1), upon growth on cellulose and plant biomass (3,4). The first CDHs, initially named cellobiose oxidase, were discovered as enzymes able to catalyze the cellobiose-dependent reduction of quinones (5,6).…”