Abstract
Biomass is abundant, renewable and useful for biofuel production as well as chemical priming for plastics and composites. Deconstruction of biomass by enzymes is perceived as recalcitrant while an inclusive breakdown mechanism remains to be discovered. Fungi such as Myceliophthora thermophila M77 appear to decompose natural biomass sources quite well. This work reports on this fungus fermentation property while producing cellulolytic enzymes using natural biomass substrates. Little hydrolytic activity was detected, insufficient to explain the large amount of biomass depleted in the process. Furthermore, this work makes a comprehensive account of extracellular proteins and describes how secretomes redirect their qualitative protein content based on the nature and chemistry of the nutritional source. Fungus grown on purified cellulose or on natural biomass produced secretomes constituted by: cellobiohydrolases, cellobiose dehydrogenase, β-1,3 glucanase, β-glucosidases, aldose epimerase, glyoxal oxidase, GH74 xyloglucanase, galactosidase, aldolactonase and polysaccharide monooxygenases. Fungus grown on a mixture of purified hemicellulose fractions (xylans, arabinans and arabinoxylans) produced many enzymes, some of which are listed here: xylosidase, mixed β-1,3(4) glucanase, β-1,3 glucanases, β-glucosidases, β-mannosidase, β-glucosidases, galactosidase, chitinases, polysaccharide lyase, endo β-1,6 galactanase and aldose epimerase. Secretomes produced on natural biomass displayed a comprehensive set of enzymes involved in hydrolysis and oxidation of cellulose, hemicellulose-pectin and lignin. The participation of oxidation reactions coupled to lignin decomposition in the breakdown of natural biomass may explain the discrepancy observed for cellulose decomposition in relation to natural biomass fermentation experiments.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-016-0276-y) contains supplementary material, which is available to authorized users.
Highlights
Lignocellulosic biomass polymers are a massive and renewable source for production of biofuels and biochemicals, because they trap about 60% of all sugars produced by plants on earth
This recalcitrance towards the degradation of cellulose is abundantly illustrated in the repertoire of cellulose degrading enzymes produced by microorganisms that try to use this polymer as a carbon source (Segato et al 2014)
Extracellular protein and expected enzyme activities, cellulase (measured as activity on filter paper (FPU), xylanase and β-glucosidase accumulated in the medium over time reaching a peak at or around 96 h
Summary
Lignocellulosic biomass polymers are a massive and renewable source for production of biofuels and biochemicals, because they trap about 60% of all sugars produced by plants on earth. The disconnection of the glucan chain from crystalline cellulose fibers has been proposed to be the bottleneck in enzymatic hydrolysis of cellulose (Himmel and Bayer 2009) This recalcitrance towards the degradation of cellulose is abundantly illustrated in the repertoire of cellulose degrading enzymes produced by microorganisms that try to use this polymer as a carbon source (Segato et al 2014). For comprehensive reviews of hydrolytic biomass breakdown refer to (Benz et al 2013; Coutinho et al 2009; Glass et al 2013; Martens-Uzunova and Schaap 2009; Segato et al 2014)
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