Organisms that Degrade Wood

Depending on where and how they are used, wood products may be attacked by a range of biodeteriorogens that include fungi, insects, marine borers and bacteria. 

Fungi require air, moisture and nutrients in order to invade and colonize wood. 

Mould fungi can be broadly classified as being saprophytic organisms that utilize simple sugars and other carbohydrates derived from cell lumens. Since they do not attack the wood cell wall structure they do not cause significant decreases in wood mechanical properties. Moulds are noticeable as fuzzy or powdery growths with colours ranging from white to black. They primarily affect the aesthetic appearance of the wood. 

Unfortunately, to the layman all or any fungal growth associated with sawn or round wood is of considerable concern. Not only is there a misconception that the structure is in danger of premature collapse but in extreme cases hysteria ensues out of concern about exposure to mould spores (Uzonovic et al., 2003). Moulds can cause allergic or asthmatic reactions in some sensitive people and a few moulds produce potentially toxic substances however anything more serious than allergic or irritant symptoms is rare. 

If harvesting and milling is undertaken efficiently a prophylaetie dip or spray immediately after sawing may provide the necessary short term proteetion against mould and sapstain during seasoning, storage or export. 

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The organisms that degrade natural fibers live either on the exterior surface of the fibers, as most often is the case with cotton, or in the fiber lumina as is necessary in the case of wood. Here they secrete extracellular enzymes that catalyze the dissolution of the high-polymeric constituents of the fiber to soluble products that can be assimilated and metabolized by the organisms. 

When wood is laid down by the cambium of a living tree, two major types of wood cells are formed—thick-walled fiber cells that make wood strong and thin-walled parenchyma cells in which reserve foods are stored. Wood fiber cells die a few days or weeks after they are formed and lose their cytoplasmic contents as soon as they become functional in water transport. Thus, mature wood fiber cells consist almost entirely of cell wall polymers—cellulose, hemicellu-loses, and lignin. For this reason, wood fiber cells can be degraded only by organisms that have the ability to decompose these structurally complex high-polymeric materials. 

C. accounts for more of the earth s biomass than any other compound. The total amount is equivalent to about 50% of the carbon dioxide in the atmosphere about 100 billion metric tonnes are produced each year. It is degraded by organisms that possess Cellulases (see) lower plants, wood-destroying fungi and some bacteria. Termites, ruminants and some rodents harbor symbiotic bacteria in their digestive tracts which enable them to utilize cellulose. In animals that cannot digest it (e.g. humans and carnivores), C. is a ballast substance. C. is a very important industrial product, obtained primarily by acid (sulfite... 

Fungi that may produce corrosive byproducts in their metabolism, such as organic acids. Apart from metals and alloys these can also degrade organic coatings and wood. 

A major concern when remediating wood-treatment sites is that pentachlorophenol was often used in combination with metal salts, and these compounds, such as chromated copper—arsenate, are potent inhibitors of at least some pentachlorophenol degrading organisms (49). Sites with significant levels of such inorganics may not be suitable candidates for bioremediation. 

It is very seldom that only a single substrate is present. It is therefore important to examine how the regulation of degradative pathways may be affected and, in particular, whether the simultaneous presence of other contaminants has an adverse effect. In addition, some of the components of a contaminant may directly inhibit degradation by toxification of the relevant organism. The example of azaarenes in groundwater at a wood preservation site that inhibit PAH degradation (Lantz et al. 1997) is noted in Chapter 14. 

Lantz SE, MT Montgomery, WW Schultz, PH Pritchard, BJ Spargo, and JG Mueller 1997 Constituents of an organic wood preservative that inhibit the fluoranthene-degrading activity of Sphingomonas paucimo-bilis strain EPA505. Environ Sci Technol 31 3573-3580. 

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