Secretome analysis of the basidiomycete Phanerochaete chrysosporium grown on ammonia-treated lignocellulosic biomass from birch wood

Kiyoshi Sakuragi,Kiyohiko Igarashi,Chiaki Hori,Masahiro Samejima

doi:10.1007/s10086-018-1770-4

Abstract

Ammonia pretreatment is a promising technique for enhancing enzymatic saccharification of lignocellulosic biomass. However, an enzymatic cocktail suitable for the breakdown of pretreated biomass samples is still being developed. The basidiomycete Phanerochaete chrysosporium is a well-studied fungus with regard to bioconversion of lignocellulosic biomass. In the present work, we analyzed proteins secreted by P. chrysosporium grown on untreated and ammonia-treated birch wood meal. Fungal growth, xylanase activity, and extracellular protease activity increased in the media containing the ammonia-treated biomass; however, cellulase production decreased compared to that observed in the untreated biomass. Secreted extracellular proteins were separated by two-dimensional electrophoresis and identified by liquid chromatography ion–trap mass spectrometry. Fifty-five spots corresponding to secreted proteins were chosen for further analysis. In the culture with ammonia-treated biomass, the relative concentration of a xylanase belonging to glycoside hydrolase (GH) family 11 increased, while acetyl xylan esterases belonging to carbohydrate esterase family 1 decreased. Moreover, GH family 10 xylanases were promoted proteolysis in the culture of ammonia-treated biomass, leading to the loss of family 1 carbohydrate-binding modules. These results indicated that P. chrysosporium produced enzymes related to the recognition of structural changes on xylan with de-acetylation and introduction of nitrogen by ammonia pretreatment of birch wood meal.

Highlights

Lignocellulosic biomass, the most abundant renewable organic carbon source on earth, consists mainly of cellulose, hemicellulose, and lignin [1]
The changes in protein concentration of the cultures were not significantly different after 3 days of cultivation (p = n. s.), ammonia pretreatment greatly enhanced the growth of P. chrysosporium
We have recently reported that ammonia pretreatment is effective for improving the enzymatic saccharification of hardwood biomasses such as birch wood with high xylan and low lignin contents [10]

Summary

Introduction

Lignocellulosic biomass, the most abundant renewable organic carbon source on earth, consists mainly of cellulose, hemicellulose, and lignin [1]. Various pretreatment methods are used to enhance the enzymatic saccharification of lignocellulosic biomass [2]. One of the most promising approaches for lignocellulosic biomass from grass plants is pretreatment with liquefied ammonia, and this methodology has been extensively investigated [3,4,5]. The ammonia cleaves ester bonds in lignocellulosic biomass and generates amides [6, 7]. It has been demonstrated that ammonia pretreatment alters the polymorphic form of crystalline cellulose with a low water content, transforming the natural crystalline form (cellulose I) to cellulose I III [8], which is far more susceptible to enzymatic degradation [9].

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