Hyperthermophilic endoglucanase for in planta lignocellulose conversion

Holger Klose,Juliane Röder,Rainer Fischer,Michele Girfoglio,Ulrich Commandeur

doi:10.1186/1754-6834-5-63

Abstract

BackgroundThe enzymatic conversion of lignocellulosic plant biomass into fermentable sugars is a crucial step in the sustainable and environmentally friendly production of biofuels. However, a major drawback of enzymes from mesophilic sources is their suboptimal activity under established pretreatment conditions, e.g. high temperatures, extreme pH values and high salt concentrations. Enzymes from extremophiles are better adapted to these conditions and could be produced by heterologous expression in microbes, or even directly in the plant biomass.ResultsHere we show that a cellulase gene (sso1354) isolated from the hyperthermophilic archaeon Sulfolobus solfataricus can be expressed in plants, and that the recombinant enzyme is biologically active and exhibits the same properties as the wild type form. Since the enzyme is inactive under normal plant growth conditions, this potentially allows its expression in plants without negative effects on growth and development, and subsequent heat-inducible activation. Furthermore we demonstrate that the recombinant enzyme acts in high concentrations of ionic liquids and can therefore degrade α-cellulose or even complex cell wall preparations under those pretreatment conditions.ConclusionThe hyperthermophilic endoglucanase SSO1354 with its unique features is an excellent tool for advanced biomass conversion. Here we demonstrate its expression in planta and the possibility for post harvest activation. Moreover the enzyme is suitable for combined pretreatment and hydrolysis applications.

Highlights

The enzymatic conversion of lignocellulosic plant biomass into fermentable sugars is a crucial step in the sustainable and environmentally friendly production of biofuels
The expression vectors were introduced into A. tumefaciens strain GV3101, which was infiltrated into tobacco leaves
Hyperthermophilic cellulases like the endoglucanase SSO1354 from S. solfataricus combine both features

Summary

Introduction

The enzymatic conversion of lignocellulosic plant biomass into fermentable sugars is a crucial step in the sustainable and environmentally friendly production of biofuels. Pretreatment methods are usually harsh, involving strong acidic or alkaline solutions, high temperatures and pressures, and the presence of organic solvents [1]. These are features of contemporary chemical processing methods such as diluted acid hydrolysis, ammonia fiber explosion (AFEX) and organosolv, the use of ionic liquids to dissolve lignocellulose has recently emerged as a promising alternative for biomass pretreatment [2]. The greatest potential benefit offered by plants is that biomass-degrading enzymes can be produced within the plant biomass itself This approach can only be successful if the enzymatic activity does not inhibit plant growth and development, and biomass pretreatments do not destroy the enzymes [6,7]

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Conclusion