An investigation of selected effects of environment on the dry rot fungus Serpula Lacrimans

  • Gordon Low

    Student thesis: Doctoral Thesis


    Comparisons were made between the sensitivities of unique ‘wild’ isolates and domestic isolates of the dry rot fungus, Serpula lacrymans, to temperature, water potential and pH. Comparisons were also made between their capacities of timber decay. The ‘wild’ Himalayan isolates displayed slightly less marked sensitivities to high and low temperature and lowered water potential, yet the isolates were equally tolerant of pH. In general, the linear growth rates of the domestic isolates proved to be twice those of the ‘wild’ Himalayan set, whereas little variation occurred between their rates of timber decay. This study also resulted in the first isolation and reliable identification of ‘wild-growing’ S. lacrymans collected in Europe. The main part of the project involved the construction of novel chambers in order to examine the effects of lowered humidity and moving air flow on the activity of S. lacrymans. In the smallest and simplest of these, its growth and timberdecaying activities could be stopped by incubation at 86% relative humidity or by the application of a pumped air flow rate of 2.5 litres per minute; however, S. lacrymans was not inactivated until more-stressful conditions were applied. In addition, an intermediate rate of air flow provoked marked directional growth away from the stress. Furthermore, the introduction of stone, brick and plaster into these models encouraged the capacities of timber decay and mycelial growth. The use of a larger and more representative model incorporating simulated flooring and plaster walling within glass tanks revealed differences in the appearances and patterns of colonisation by S. lacrymans depending upon whether aged or new materials were used. Treatments involving air drying by fans caused both a shrivelling and a loss of viability of the fungus only when there was no ‘reservoir’ of water available; when there was water present, latent activity remained. An elaboration of this experimental design tested the effects of a combined biological and environmental treatment. Subsequently, the application of Trichoderma harzianum, a known antagonist of S. lacrymans, proved not to be an effective remedial treatment on its own, but appeared to impart a mildly protective effect when combined with a drying regime. Importantly, in the latter situation T. harzianum caused a severe degradation of the part of the colony responsible for the uptake of water in S. lacrymans. Another workshop-scale model simulating more authentically a damp sub-floor space and a cavity behind aged plaster walling was developed. When respective treatments by fan drying and passive ventilation were compared, the former were more effective, but its efficacy could be augmented by incorporating low-level passive ventilation via discreet vents. In this manner, a successful remedial treatment of S. lacrymans could be effected, though the prevalence of mould could prove to be undesirable in practice. However, some samples of this displayed antagonistic effects against S. lacrymans. A further experiment was designed to test the effects of air drying on the production of the stress-protective carbohydrate trehalose and of some associated solutes by S. lacrymans. In contrast to reports of some other organisms, no definite stockpiling of any of the compounds occurred. A final series of experiments revealed that S. lacrymans removed calcium, silicon and iron from sandstone and calcium, sulphur and iron from aged plaster; these elements were sequestered on its hyphae, especially in the form of calcium oxalate. Degradation of the sandstone was implicit but not obvious microscopically. Furthermore, S. lacrymans transported iron from these building materials through its mycelial system. An attempt to determine the effects of separate minerals in sandstone and plaster on timber decay revealed few variations.
    Date of AwardMar 2000
    Original languageEnglish
    SponsorsHistoric Scotland
    SupervisorJohn W. Palfreyman (Supervisor)

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