Microbial and Enzymatic Degradation of Wood and Wood Components

The oil crisis during the 1970s turned interest towards the utilization of renewable resources and towards lignocellulosics in particular. The 1970s were also the cradle period of biotechnology, and the years when biotechnical utilization of lignocellulosic waste from agriculture and forestry gained priori­ ty. This was a logical conclusion since one of nature's most important biologi­ cal reactions is the conversion of wood and other lignocellulosic materials to carbon dioxide, water and humic substances. However, while biotechnology in other areas like medicine and pharmacology concerned production of expen­ sive products on a small scale, biotechnical utilization and conversion of ligno­ cellulosics meant production of inexpensive products on a large scale. Biotechnical utilization of lignocellulosic materials is therefore a very difficult task, and the commercial utilization of this technology has not progressed as rapidly as one would have desired. One reason for this was the lack of basic knowledge of enzyme mechanisms involved in the degradation and conversion of wood, other lignocellulosics and their individual components. There are also risks associated with initiating a technical development before a stable platform of knowledge is available. Several of the projects started with en­ thusiasm have therefore suffered some loss of interest. Also contributing to this failing interest is the fact that the oil crisis at the time was not a real one. At present, nobody predicts a rapid exhaustion of the oil resources and fuel production from lignocellulosics is no longer a high priority.

Contenu

1 Morphological Aspects of Wood Degradation by Fungi and Bacteria.- 1.1 Morphology of Wood and Wood Components.- 1.2 Wood Degradation by White-Rot Fungi.- 1.3 Wood Degradation by Brown-Rot Fungi.- 1.4 Wood Degradation by Soft-Rot Fungi.- 1.5 Wood Degradation by Bacteria.- 2 Biodegradation of Cellulose.- 2.1 The Structure and Biosynthesis of Cellulose.- 2.1.1 The Chemical Structure of Cellulose.- 2.1.2 Cellulose Biosynthesis: Biochemical Studies.- 2.1.3 The Cellulose Microfibril.- 2.2 Cellulolytic Fungi.- 2.3 Cellulolytic Enzymes.- 2.3.1 The Old Concept.- 2.3.2 Hydrolytic Enzymes.- 2.3.3 Oxidative Enzymes.- 2.3.4 Phosphorolytic Enzymes.- 2.4 Assay of Enzymes Participating in Cellulose Degradation.- 2.4.1 Endo-1,4-?-Glucanase Activity.- 2.4.2 Exo-1,4-?-Glucanase Activity.- 2.4.3 1,4-?-Glucosidase Activity.- 2.4.4 Oxidative Enzymes.- 2.4.5 Phosphorolytic Enzymes.- 2.5 Cellulose Degradation by White-Rot, Brown-Rot, Soft-Rot, and Anaerobic Fungi.- 2.5.1 White-Rot Fungi.- 2.5.2 Brown-Rot Fungi.- 2.5.3 Soft-Rot Fungi.- 2.5.4 Anaerobic Fungi.- 2.6 Cellulose Degradation by Bacteria.- 2.6.1 Aerobic Bacteria.- 2.6.2 Anaerobic Bacteria.- 2.7 Regulation of Cellulase Synthesis.- 2.8 Synergistic Mechanisms Involved in Cellulose Degradation.- 2.9 Examples of Applications of Cellulolytic Microorganisms and Their Enzymes.- 2.9.1 Fermentation of Lignocellulosic Materials to Protein.- 2.9.2 Enzymatic Saccharification of Lignocellulosic Materials for Ethanol Production.- 3 Biodegradation of Hemicelluloses.- 3.1 The Structures of Hemicelluloses.- 3.1.1 Softwood Hemicelluloses.- 3.1.2 Hardwood Hemicelluloses.- 3.2 Biosynthesis of Hemicelluloses.- 3.3 Xylanolytic Enzymes.- 3.3.1 Endo-1,4-?-d-Xylanases.- 3.3.2 1,4-?-d-Xylosidases.- 3.3.3 ?-Arabinosidase.- 3.3.4 ?-d-Glucuronidase.- 3.3.5 Acetyl(Xylan) Esterase.- 3.4 Mannan-Degrading Enzymes.- 3.4.1 Endo-1,4-?-d-Mannanases.- 3.4.2 1,4-?-d-Mannosidase.- 3.4.3 ?-Galactosidase.- 3.5 Examples of Applications of Hemicellulolytic Organisms and Their Enzymes.- 4 Biodegradation of Lignin.- 4.1 Biosynthesis and Structure of Lignin.- 4.2 Lignin Preparations and Methods for Studying Lignin Biodegradation.- 4.3 Lignin Degradation by White-Rot Fungi.- 4.3.1 Physiological Demands, Secondary Metabolism, and Veratryl Alcohol Production in White-Rot Fungi.- 4.3.2 Influence of Nitrogen on Secondary Metabolism and Lignin Degradation.- 4.3.3 Influence of Carbon Source on Lignin Degradation.- 4.3.4 Influence of Agitation and Other Cultivation Conditions on Lignin Degradation and Ligninase Production.- 4.3.5 Influence of Oxygen and Carbon Dioxide on Lignin Degradation. Anaerobic Degradation of Lignin and Related Compounds.- 4.4 Chemistry of Lignin Degraded by White-Rot Fungi.- 4.5 Biochemistry of Lignin Degradation.- 4.5.1 Oxygen Radicals and Lignin Degradation.- 4.5.2 The Phenoloxidases Laccase and Peroxidase Including Manganese-Dependent Pexoxidase.- 4.5.3 Ligninase/Lignin Peroxidase.- 4.5.4 Biomimetic Oxidation of Lignin Models.- 4.5.5 H2O2-Producing Enzymes.- 4.5.6 Quinone-Reducing Enzymes.- 4.5.7 Cleavage of Methoxyl Groups by Wood-Rotting Fungi.- 4.6 Metabolism of Monomeric Lignin-Related Compounds.- 4.7 Lignin Degradation by Brown-Rot, Soft-Rot, and Other Fungi.- 4.7.1 Brown-Rot Fungi.- 4.7.2 Soft-Rot Fungi.- 4.7.3 Other Fungi.- 4.8 Lignin Degradation by Bacteria.- 4.8.1 Actinomycetes.- 4.8.2 Other Bacteria.- 4.9 Potential Applications of White-Rot Fungi.- 4.9.1 Biopulping and Biomechanical Pulping.- 4.9.2 Treatment of Wood and Straw to Produce Feed and Food.- 4.9.3 Treatment of Spent Kraft Bleach Liquors.- 4.9.4 By-Products from Lignin.- 4.10 Some Examples of Future Research Possibilities.- References.