Fungi and Lignocellulosic Biomass E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 555

Veröffentlichungsjahr: 2012

Beschreibung

Harnessing fungi's enzymatic ability to break down lignocellulolytic biomass to produce ethanol more efficiently and cost-effectively has become a significant research and industrial interest. Fungi and Lignocellulosic Biomass provides readers with a broad range of information on the uses and untapped potential of fungi in the production of bio-based fuels. With information on the molecular biological and genomic aspects of fungal degradation of plant cell walls to the industrial production and application of key fungal enzymes, chapters in the book cover topics such as enzymology of cellulose, hemicelluloses, and lignin degradation. Edited by a leading researcher in the field, Fungi and Lignocellulosic Biomass will be a valuable tool in advancing the development and production of biofuels and a comprehensive resource for fungal biologists, enzymologists, protein chemists, biofuels chemical engineers, and other research and industry professionals in the field of biomass research.

Leseprobe

Contents

Cover

Title Page

Copyright

Preface

Chapter 1: The Plant Biomass

1.1 The Structure of Plant Cell Wall

1.2 Chemical and Physicochemical Properties of the Major Plant Cell Wall Constituents

1.3 Abundant Sources of Carbohydrate Polymers and Their Monomer Composition

1.4 Biosynthesis of Plant Cell Wall Polymers

1.5 Strategies for Manipulating Wall Composition

Chapter 2: The Actors: Plant Biomass Degradation by Fungi

2.1 Ecological Perspectives

2.2 The Major Three Mechanisms of Lignocellulose Degradation by Fungi

2.3 Plant Cell Wall Degradation by Plant Pathogenic Fungi

2.4 Anaerobic Fungi

Chapter 3: The Tools—Part 1: Enzymology of Cellulose Degradation

3.1 General Properties and Classification of Enzymes That Hydrolyze Polysaccharides

3.2 Fungal Cellulolytic Enzymes

3.3 Nonenzymatic Proteins Involved in Cellulose Hydrolysis

Chapter 4: The Tools—Part 2: Enzymology of Hemicellulose Degradation

4.1 Xyloglucan Hydrolysis

4.2 Degradation of the Xylan Backbone

4.3 Degradation of the Galactomannan Backbone

4.4 Degradation of Pectin

4.5 Accessory Glycoside Hydrolases for Hemicelluloses Degradation

4.6 Other Accessory Enzymes

Chapter 5: The Tools—Part 3: Enzymology of Lignin Degradation

5.1 Lignin Peroxidase

5.2 Manganese Peroxidase

5.3 Versatile Peroxidase

5.4 Dye-Oxidizing Peroxidase

5.5 Laccases

5.6 Enzymes Generating Hydrogen Peroxide

5.7 Cellobiose Dehydrogenase

5.8 Enzymes Essential for Oxalic Acid Formation

5.9 Glycopeptides

Chapter 6: Catabolic Pathways of Soluble Degradation Products from Plant Biomass

6.1 Uptake of Mono- and Oligosaccharides

6.2 Metabolism of d-Glucose and d-Mannose

6.3 Catabolism of d-Galactose

6.4 Catabolism of Pentoses

6.5 Catabolism of Hexuronic Acids

Chapter 7: Regulation of Formation of Plant Biomass-Degrading Enzymes in Fungi

7.1 The Cellulase Inducer Enigma

7.2 Inducers for Hemicellulases

7.3 Transcriptional Regulation of Cellulase and Hemicellulase Gene Expression

7.4 Regulation of Ligninase Gene Expression

Chapter 8: The Fungal Secretory Pathways and Their Relation to Lignocellulose Degradation

8.1 The Fungal Secretory Pathway

8.2 Protein Glycosylation

8.3 Strategies for Improvement of the Fungal Secretory Pathway

Chapter 9: Production of Cellulases and Hemicellulases by Fungi

9.1 Fungal Producer Strains

9.2 Strain Improvement

9.3 Cellulase Production

Chapter 10: Production of Fermentable Sugars from Lignocelluloses

10.1 Pretreatment Technologies

10.2 Hydrolysis

Chapter 11: Lignocellulose Biorefinery

11.1 Ethanol

11.2 n-Butanol

11.3 Advanced Biofuel Alcohols

11.4 Lactic Acid

11.5 Succinic Acid

11.6 Xylitol

11.7 1,3-Propanediol

11.8 Polyhydroxyalkanoate

11.9 Other Products

11.10 Refinement by Chemical Processes

Acknowledgments

References

Index

Advertisement

This edition first published 2013 © 2013 by John Wiley & Sons, Inc.

Wiley-Blackwell is an imprint of John Wiley & Sons, formed by the merger of Wiley's global Scientific, Technical and Medical business with Blackwell Publishing.

Editorial offices: 2121 State Avenue, Ames, Iowa 50014-8300, USA The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK 9600 Garsington Road, Oxford, OX4 2DQ, UK

For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com/wiley-blackwell.

Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by Blackwell Publishing, provided that the base fee is paid directly to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923. For those organizations that have been granted a photocopy license by CCC, a separate system of payments has been arranged. The fee codes for users of the Transactional Reporting Service are ISBN-13: 978-0-4709-6009-7/2013.

Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought.

Library of Congress Cataloging-in-Publication Data

Kubicek, C. P. (Christian P.) Fungi and lignocellulosic biomass / Christian P. Kubicek ; with figures by Irina S. Druzhinina and Lea Atanasova. p. cm. Includes bibliographical references and index. ISBN 978-0-470-96009-7 (hardcover : alk. paper) 1. Lignocellulose–Biodegradation. 2. Fungi–Biotechnology. 3. Biomass energy. I. Title. TP248.65.L54K82 2012 662′.88–dc23 2012010996

A catalogue record for this book is available from the British Library.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

Preface

The advent of the third millennium has been and is still characterized by an increasing concern about the dependency of the human society on oil reserves and on the consequences for our planet as a whole from the rising carbon dioxide levels. A large part of this fossil carbon is used for generation of energy, for which alternatives such as nuclear, solar-electric, solar-thermal, hydroelectric, or geothermal have been proposed or developed and may well function at the individual and smaller community level. However, at the time of this writing, replacement of fossil fuels for long-distance road transport or aviation is not in sight. In addition, about 10% of fossil carbon is currently used by the petrochemical industry for the production of components required for the manufacture of a wide array of goods that form an essential part of our everyday life.

The only reasonable alternative to these major problems of our society is the use of carbon sources that are permanently available in large amounts, and which can be used in a carbon dioxide neutral way. Quantitatively, plant biomass is by far the only carbon source that can fulfill these requirements: it arises by carbon dioxide fixation during photosynthesis, and its dry weight consists mainly of three polymers (cellulose, hemicelluloses, and lignin) whose monomer constituents (hexose and pentose sugars and phenylpropan compounds) can be converted to useful starting materials for industry by fermentation or biotransformation (the so-called biorefinery concept). Owing to the above-cited problems with energy, most of the research on the use of plant biomass has gone into liquid biofuels, particularly ethanol.

A key step in this plant biomass for “biofuels/biorefineries” concept is the production of the above-named monomeric components in a sufficiently high concentration using technologies that do not produce hazardous by-products. Enzymatic hydrolysis is the only means that can theoretically fulfill this purpose and has been investigated to this end since the early 1960s. These studies have revealed that particularly fungi can form cellulolytic, hemicellulolytic, and ligninolytic enzymes, and some of them (notably Trichoderma reesei, the current paradigm of cellulase and hemicellulase research) have been used with success for the production of enzymes used in the hydrolysis of plant cell wall material.

While the basic path of the road from biomass to biofuels/biorefineries thus seems to be straightforward, and has led to the presentation of several demonstration plants in the United States, Canada, and Europe, there are still several large stones to remove from this road. One of the biggest of them is to render the price for enzymatic hydrolysis and subsequent production of compounds like ethanol compatible or better lower than the prices for liquid fossil fuels, which requires improvement of several steps such as activity and composition of the enzymes used, the hydrolysis process, yield of the desired product, and appropriate uses for side products and not-used components from the hydrolysate (e.g., xylose or lignin). Obviously, solutions to overcome these bottlenecks must come from an interdisciplinary treatment of these processes, involving contributions from botany, microbiology, biochemistry, biotechnology, and biochemical engineering.

The focus of this book is on the fungal enzymes that are required and applied for lignocellulose hydrolysis, but does not limit this treatment only to a description of the enzyme inventory (Chapters 3–5). Instead, it attempts to relate this main focus to the other areas that influence the process as a whole, such as composition and availability of the plant biomass (Chapter 1) and the different modes of how fungi make this material available for their own lifestyle (Chapter 2), as well as a treatment of the biochemical pathways for the metabolism of the arising monomers (Chapter 6), the regulation of enzyme formation (Chapter 7), and the cell biology of their secretion (Chapter 8). Finally, the last three chapters deal with the selection of appropriate producer strains and their fermentation (Chapter 9), the pretreatment and hydrolysis of the plant biomass (Chapter 10), and with the processes for production of biofuels and biorefineries (Chapter 11).

This book has been written in an attempt to serve both as a professional reference for all people who work in this area and as an introduction into the field for all those who are generally interested in the topic, from academic institutions and research teams to teachers, as well as graduate and postgraduate students. Toward this purpose, I have refrained from going into too much detail with many aspects, but have instead provided an extensive list of both original and review references that can be used to obtain a yet deeper information on individual topics. Still, I have to apologize to all those colleagues whose work is not cited, and to those I refer only by citation of a review. This is not due to neglect but only due to the necessity to keep the references within a reasonable size.

Chapter 1

The Plant Biomass

1.1 The Structure of Plant Cell Wall

When we talk of plant biomass in terms of its use for biofuel and other biorefineries, we mostly mean the plant cell wall that makes up for more than 50% of the plants dry weight. This most outside located structure of the plant cell is also its most distinguishing feature, and because of its rigidity an essential component for their sedentary lifestyle. This rigidity also provides the strength to withstand mechanical stress and forms and maintains the plants shape. Despite this rigidity, nevertheless, the cell wall is a dynamic and metabolically active entity that plays crucial roles in growth, differentiation, and cell-to-cell communication and acts as a pressure vessel that prevents overexpansion when water enters the cell (Raven et al., 1999).

Plant cell walls typically consist of three layers: the “primary cell wall” (a rather thin but continuously extending layer that is produced by growing cells), the “secondary cell wall” (a thick layer that is formed inside the primary cell wall after termination of cell growth), and the “middle lamella” (the outermost layer that forms an interface between secondary walls of adjacent plant cells and glues them together) (Figure 1.1).

Figure 1.1 Organization of the different layers of the plant cell wall.

Figure 1.2 Schematic diagram of the three-dimensional arrangement of the main polymers in the primary plant cell wall. The top sheet represents the middle lamella, the bottom sheet represents the plasma membrane; and the area in between represents the primary cell wall. Bright gray threads symbolize pectin, dark gray rectangular lines indicate hemicelluloses, small globes indicate soluble proteins, and the gray tubes indicate the cellulose microfibrils.

The primary cell wall consists of the polysaccharides cellulose, hemicellulose, and pectin (Rose et al., 2004). The cellulose thereby aggregates to microfibrils that are covalently linked to hemicellulosic chains and form a cellulose—hemicellulose network that is embedded in the pectin matrix. The secondary wall is formed in some plants between the plant cell and primary wall when either a maximum size or a critical point in development has been reached and makes the plant cells rigid. It is made up from cellulose, hemicelluloses (mostly xylan), and lignin. The latter is a complex polymer of aromatic aldehydes that fills the spaces between cellulose, hemicellulose, and pectin components of the cell wall. Because of its hydrophobic nature, it drives out water and so strengthens the wall. In wood, three layers of the secondary cell wall, referred to as the S1, S2, and S3 lamellae, are found that result from different arrangements of the cellulose microfibrils (Mauseth, 1988; Figure 1.1). The first outermost layer—the S1 lamella—has both left- and right-handed microfibril helices; in contrast, the S2 (middle) and S3 (innermost) lamellae only comprise a single helix of microfibrils, although with opposite handedness to each other. During formation of the secondary cell wall, lignification takes place in the S1 and S2 but not S3 lamellae and also in the primary wall and middle lamella (Levy and Staehlin, 1992; Reiter, 2002; Popper, 2008). This arrangement allows the cellulose microfibrils to become embedded and fixed within the lignin, similar to steel rods that become embedded in concrete (Figure 1.2).

In addition, structural proteins (1–5%) are found in most plant cell walls; they are usually classified as hydroxyproline-rich glycoproteins (HRGPs), arabinogalactan proteins (AGPs), glycine-rich proteins (GRPs), and proline-rich proteins (PRPs) (Albenne et al., 2009). The function of these proteins is not well understood. However, it is likely that the glycan moieties in these proteins can form hydrogen bonds and salt bridges to the cell wall polysaccharides, and thereby contribute to the mechanical strength to the wall. The relative composition of carbohydrates, secondary compounds, and proteins varies between plants and between the cell type and age (Levy and Staehelin, 1992; Reiter, 2002; Popper, 2008).

The secondary cell wall may also contain additional layers of lignin in xylem cell walls, and suberin in cork cell walls, that confer rigidity and contribute to the exclusion of water.

1.2 Chemical and Physicochemical Properties of the Major Plant Cell Wall Constituents

1.2.1 Cellulose

As noted earlier, cellulose is one of the principal components of both primary and secondary plant cell walls and reaches its highest abundance (40%) in the secondary cell walls. Cellulose consists of unbranched, unsubstituted 1,4-β-D-glucan chains that can reach degrees of polymerization of 2,000–6,000 and 2,000–10,000 residues in primary and secondary walls, respectively. The CH2OH side group is arranged in a trans-gauche position (a term that described the separation of two vicinal groups by a 60° torsion angle) relative to the O5–C5 and C4–C5 bonds. Because of the absence of coiling or branching, the molecule adopts an extended, rod-like conformation, aided by the equatorial conformation of the glucose residues. The multiple hydroxyl groups on the glucose from one chain can form hydrogen bonds with oxygen molecules on the same or on a neighboring chain (Figure 1.3), and so hold the chains firmly together side by side and form microfibrils with high tensile strength. This strength is one of the major sources of rigidity to the plant cell wall (Klemm et al., 2004; O’Sullivan, 1997).

Figure 1.3 The chemical structure of cellulose. Dotted lines represent hydrogen bonds.