The role of bacteria in the decay of building stone from ancient monuments was examined using the framework of Koch's postulates. This involved a stepwise approach to investigate the occurrence, nature and decay potential of bacteria on stone. Prior to investigating the occurrence of bacteria on stonework it was necessary to develop a standardised procedure of high precision for the recovery and enumeration of these bacteria. A number of different methods to remove bacteria from stone were studied including physical agitation, chemical desorption and surfactant treatment. Finally a method was adopted in which stone samples were powdered, homogenised in a dilute solution of surfactant (Tween 80) and counted on an automatic plating system. A range of growth media were used to examine three different bacterial types, namely, sulphur-oxidising, nitrifying and heterotrophic. To investigate the occurrence and distri but10n of bacteria on both sound and decayed stone extensive bacteriological surveys were conducted on stonework at two monuments, Portchester Castle and Tintern Abbey. All types of bacteria were widely distributed on both sandstone and limestone at the monuments. At each monument, significantly more sulphur-oxidising and heterotrophic bacteria were associated with severely decayed stone than undecayed stone. Electron microscopy confirmed that large populations of bacteria could be found predominantly 5-10mm below the surface of decayed stone. Approximately 200 bacteria were isolated into pure culture during the field surveys of the two monuments. All isolates were screened for decay potential using a liquid culture system involving static growth of bacteria in the presence of 1cm stone discs. From the 200 isolates, about 30 were capable of causing substantial weight loss in sandstone discs under heterotrophic conditions. Five isolates were able to cause a large weight loss using only mineral nutrients. Some isolates caused a significant weight gain in the stone discs under these conditions. Statistical analysis of the data from this decay screen indicated that weight loss of stone could be directly correlated to a decrease in pH of the medium and a release of calcium and silicate from the stone. Futher decay studies carried out on selected isolates suggested that under heterotrophic conditions the bacteria secreted quantities of organic acids in to the medium which could attack the stone. However, in the presence of an inorganic nutrient source, the generation of mineral acids may be involved. Under both conditions different stones had varying resistance to bacterial decay and this appeared to be dependent upon the level of calcite in the stone. Specific antibody techniques such as BLISA and FAT were examined and proved very useful in demonstrating the presence of certain principal decay species on samples of decayed stone.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:379170 |
| Date | January 1987 |
| Creators | Lewis, F. J. |
| Publisher | University of Portsmouth |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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