2.1 Introduction

Many different types of organisms deteriorate wood, but the greatest damage results from fungi. Decay is the most serious form of microbiological deterioration because it can cause structural failure, sometimes very rapidly. Because widespread damage to wood from decay is seldom spectacular, the tremendous economic and resource loss resulting from decay is often overlooked. This oversight is exemplified by a failure to recognize that biodeterioration of wood products is important and that extending the service life of wood is a sure way to prolong the available timber supply. Knowledge about the biochemical systems of decay fungi can serve another purpose as well. Decay fungi can be used for the bioconversion of lignified tissue, such as biopulping or enzymatic treatment of pulps (Kirk and Hammel, 1992). Recent research has advanced our understanding of how wood components are degraded by microorganisms and their enzymes, permitting rapid advances in bio-technology (Wainwright, 1992).

The most important and potent wood-destroying organisms are white- and brown-rot fungi, which attack various components of the wood cell wall. Most white-rot fungi utilize cellulose and hemicelluloses at approximately the same rate relative to the original amounts present, whereas lignin is usually utilized at a some-what faster relative rate. A few white-rot fungi remove lignin and hemicelluloses preferentially, but ultimately they degrade all wood cell wall components. White-rot fungi cause the wood to become pale, eventually reducing it to a fibrous, whitish mass. Brown-rot fungi utilize cell wall hemicelluloses and cellulose, leaving the lignin essentially undigested. However, brown-rot fungi do modify lignin as indi-cated by demethylation and accumulation of oxidized polymeric lignin-degradation products. These fungi cause the wood to darken, shrink and break into brick-shaped pieces that crumble easily into a brown powder. Brown- and white-rot fungi decay wood by distinctly different mechanisms. However, in spite of considerable research the biochemical bases for the different morphological and chemical changes are not clear (Figures 2.1 and 2-2). Many factors have hindered progress - in particular, the complexity of the wood substrate and the multiplicity of enzymes produced. The applications of classical and molecu-lar genetics to wood-degradative systems of decay fungi have progressed rapidly and can be used to elucidate the mechanisms of wood degradation. This chapter reviews the decomposition of wood by white- and brown-rot fungi and discusses how recent advances in biotechnology and their application to the study of wood decay have augmented knowledge about the fungal mechanisms of wood deterioration. White-rot fungi have received by far the most attention, probably because they produce more enzymes that may have biotechnological application.

• biodeterioration : brown rot, white rot
• fungi and molds in buildings and their envelopes : brown rot, white rot

1. Antagonistic properties of Gliocladium virens against wood attacking fungi
2. Biodeterioration of wood
3. Decay of wood and wood-based products above ground in buildings, Mechanism of Brown-Rot Decay: Paradigm or Paradox