Serpula lacrymans - Brown Rot Fungus

serpula lacrymans - dry rot fungus

Serpula lacrymans is one of the fungi that causes damage to timber referred to as dry rot and is considered to be the most damaging destroyer of indoor wood construction materials in the United Kingdom.  Serpula lacrymans is well known in the building industry for its ability to spread through buildings causing significant damage to wooden structures. Serpula lacrymans spreads by means of thick mycelial cords that develop from a wood food base in damp timbers and grow at a rate of several millimetres per day. Serpula lacrymans can grow through masonry and behind plaster until they reach and colonize wooden structures. After a period of extensive growth the fungus reaches a stage where it can produce large fruiting bodies. These fruiting bodies are characteristic by sponge-like structures releasing large quantities rusty-red spores.

For Serpula lacrymans to spread and proliferate through the building it needs to read a suitable food base (timber). The initial colonization of timber structures starts either from released spores which settle of the suitable surfaces or by mycelial growth. A damp masonry and timber house presents the fungus with a similar environment to the forest floor of the temperate forest where the species evolved.

Serpula lacrymans requires relatively damp wood and very high relative humidity to establish itself and therefore it is unlikely to attack well-constructed and maintained building. The dry rot fungus is reported to survive in infected wood that has dried out, particularly if drying is slow, when it can form monokaryotic mycelium that develops arthrospores. Survival for a year or longer is reported if the temperatures don’t drop below 6C.  Optimum temperature for growth and spread of Serpula lacrymans is around 20–22C. Serpula lacrymans often grows near ventilation shafts which show a preference for concentrated oxygen. A moisture content of 30 to 40 percent is its ideal level in wood to promote fruit body formation. Serpula lacrymas uses disolved minerals from plaster and other materials to help it to breakdown of wood. 

Wood decay by Serpula lacrymans involves coordinated action of a large number of destructive enzymes and other chemical agents that act onto the wooden structure. Wood is made of polysaccharide polymers cellulose and hemicelluloses and lignin in which the celluloses are embedded. Serpula lacrymans causes passive destruction of cellulose and hemicellulose, without the total decomposition of lignin. Fungal limalents in brown rot initially grow special cells from where they grow through pits in walls between wood cells. Each filament is coated with enzymes, nonenzymic agents, and the products of cellulose decomposition. Removal of cellulose, but not lignin, results in shrinkage and darkening of the wood into the typical ‘‘cubical cracking’’ and ultimately leaves a powdery brown lignin residue.

Serpula lacrymans produces large number of digestive  enzymes, including atromentin. Atromentin and its derivatives (e.g., variegatic and pulvinic acids) are yellow, red, and orange pigments.  In Serpula lacrymans, production of these pigments, mainly variegatic acid, is induced during growth on carbon- and nitrogen rich media and accumulates in hyphae as well as being exuded into the surrounding medium during growth.