Insights into the genome and secretome of Fusarium metavorans DSM105788 by cultivation on agro-residual biomass and synthetic nutrient sources

Sophie C Brandt,Hartmut Schlüter,Wilhelm Schäfer,Arslan Ali,Bernhard Ellinger,Stefan Janssen,Martin Rühl,Christian Betzel,Carsten Wrenger,Katharina Maibach,Hévila Brognaro,Martin Gand

doi:10.1186/s13068-021-01927-9

Abstract

BackgroundThe transition to a biobased economy involving the depolymerization and fermentation of renewable agro-industrial sources is a challenge that can only be met by achieving the efficient hydrolysis of biomass to monosaccharides. In nature, lignocellulosic biomass is mainly decomposed by fungi. We recently identified six efficient cellulose degraders by screening fungi from Vietnam.ResultsWe characterized a high-performance cellulase-producing strain, with an activity of 0.06 U/mg, which was identified as a member of the Fusarium solani species complex linkage 6 (Fusarium metavorans), isolated from mangrove wood (FW16.1, deposited as DSM105788). The genome, representing nine potential chromosomes, was sequenced using PacBio and Illumina technology. In-depth secretome analysis using six different synthetic and artificial cellulose substrates and two agro-industrial waste products identified 500 proteins, including 135 enzymes assigned to five different carbohydrate-active enzyme (CAZyme) classes. The F. metavorans enzyme cocktail was tested for saccharification activity on pre-treated sugarcane bagasse, as well as untreated sugarcane bagasse and maize leaves, where it was complemented with the commercial enzyme mixture Accellerase 1500. In the untreated sugarcane bagasse and maize leaves, initial cell wall degradation was observed in the presence of at least 196 µg/mL of the in-house cocktail. Increasing the dose to 336 µg/mL facilitated the saccharification of untreated sugarcane biomass, but had no further effect on the pre-treated biomass.ConclusionOur results show that F. metavorans DSM105788 is a promising alternative pre-treatment for the degradation of agro-industrial lignocellulosic materials. The enzyme cocktail promotes the debranching of biopolymers surrounding the cellulose fibers and releases reduced sugars without process disadvantages or loss of carbohydrates.

Highlights

The transition to a biobased economy involving the depolymerization and fermentation of renewable agro-industrial sources is a challenge that can only be met by achieving the efficient hydrolysis of biomass to monosaccharides
The optimal k-mer length following assembly with SOAPdenovo was k = 15 bp, with a pkdepth of 30
The whole genome is available as a biosample from the National Center for Biotechnology Information (NCBI) under the bioproject PRJN413482, accession number JADNRB000000000

Summary

Introduction

The transition to a biobased economy involving the depolymerization and fermentation of renewable agro-industrial sources is a challenge that can only be met by achieving the efficient hydrolysis of biomass to monosaccharides. The widespread agricultural use of these two C4 crops generates large quantities of lignocellulosic biomass that can be valorized without compromising food/feed production. The main component is cellulose, the most abundant polymer on earth, consisting of linear chains of several hundred to many thousand β-(1,4)-d-glucose units. Hemicellulose, the second most abundant polymer in plant cell walls [11], features at least six different macromolecules with varying ratios of pentose (xylose and arabinose) and hexose (mostly mannose and glucose) residues [12]. Glucomannans have backbones of β-(1,4)-linked d-mannose and d-glucose, sometimes with branching β-(1,6)-glucosyl residues [14], but if α-(1,6)-linked galactose units are present the polymers are known as galactoglucomannans [15]. Pectin is a complex heteropolymer of covalently linked d-galacturonic acid and other residues, and is a significant component of sugarcane and maize bagasse [16]. The main constituents are (1) homogalacturonan, comprising linear α-(1,4)-d-galactouronic acid chains with some esterified or O-acetylated modifications; (2) rhamnogalacturonan-I, comprising repeated disaccharides of galacturonic acid and C-3 or C-2 O-acetylated rhamnosyl residues, with linear or branched α-larabinofuranosyl and/or galactopyranosyl side chains on C-4; and (3) substituted galacturonans as linear and side chain residues (rhamnogalacturonan-II), resulting in 12 types of glycosyl units that form at least 22 types of glycosidic bonds [17]

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Discussion

Conclusion