Differences in Cellulosic Supramolecular Structure of Compositionally Similar Rice Straw Affect Biomass Metabolism by Paddy Soil Microbiota.

Tatsuki Ogura,Yasuhiro Date,Jun Kikuchi,Jonathan H Badger

doi:10.1371/journal.pone.0066919

Abstract

Because they are strong and stable, lignocellulosic supramolecular structures in plant cell walls are resistant to decomposition. However, they can be degraded and recycled by soil microbiota. Little is known about the biomass degradation profiles of complex microbiota based on differences in cellulosic supramolecular structures without compositional variations. Here, we characterized and evaluated the cellulosic supramolecular structures and composition of rice straw biomass processed under different milling conditions. We used a range of techniques including solid- and solution-state nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy followed by thermodynamic and microbial degradability characterization using thermogravimetric analysis, solution-state NMR, and denaturing gradient gel electrophoresis. These measured data were further analyzed using an “ECOMICS” web-based toolkit. From the results, we found that physical pretreatment of rice straw alters the lignocellulosic supramolecular structure by cleaving significant molecular lignocellulose bonds. The transformation from crystalline to amorphous cellulose shifted the thermal degradation profiles to lower temperatures. In addition, pretreated rice straw samples developed different microbiota profiles with different metabolic dynamics during the biomass degradation process. This is the first report to comprehensively characterize the structure, composition, and thermal degradation and microbiota profiles using the ECOMICS toolkit. By revealing differences between lignocellulosic supramolecular structures of biomass processed under different milling conditions, our analysis revealed how the characteristic compositions of microbiota profiles develop in addition to their metabolic profiles and dynamics during biomass degradation.

Highlights

Plant biomass is the most abundant and important material in the terrestrial biosphere
Structural characterization of biomass processed under different milling conditions To examine the lignocellulosic supramolecular structures of biomass processed under different milling conditions, the structures were observed using Scanning electron microscopy (SEM) (Fig. 1, SEM image)
The characteristic peaks in Attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectra appeared at 890 cm21, 1027 cm21 (C–O stretching in cellulose and hemicellulose), 1103 cm21, 1120 cm21, 1145 cm21, 1232 cm21, 1311 cm21 (C–H in cellulose and C1–O vibration in syringyl derivatives), 1359 cm21 (C–H deformation in cellulose and hemicellulose), 1413 cm21 and 1502 cm21, 1450 cm21, 1604 cm21, 1720 cm21, and 2915 cm21 (C–H stretching) [7,30]

Summary

Introduction

Plant biomass is the most abundant and important material in the terrestrial biosphere. Cellulose, hemicellulose, and lignin, are complex molecules that are abundantly produced in plant cell walls. Cellulose is a linear condensation polymer comprising b (1R4)-linked D-glucose units with a degree of polymerization ranging from 100 to 20,000 [1]. Besides being the second most available biological polymer on Earth, lignin is exceptionally resistant to biodegradation [6,7]. These three persistent components form a supramolecular structure, lignocellulose, in which cellulose and hemicellulose are cemented by lignin. Lignocellulosic cell walls play important roles in strengthening plants, protecting them against microbial attack, and increasing their survival chances in severe environments [7,8,9]

Methods

Results

Conclusion