MECHANISMS OF BACTERIAL DETERIORATION OF WOOD.

摘要

Available from UMI in association with The British Library.; Bacterial decay of untreated and copper-chrome-arsenic-treated Picea abies, Pinus sylvestris, Thuya plicata, Betula verrucosa, Quercus robur and Aesculus hippocastanum exposed in seawater, riverwater and soil was investigated using light microscopy and scanning and transmission electron microscopy. The timber species, which have different lignin to cellulose contents, were exposed in the three environments for periods of 1 to 16 weeks. This allowed examination of the processes of bacterial attachment, succession, colony and consortia formation, penetration of the wood cell wall layers and subsequent decay. Bacteria associated with the exposed timbers were isolated using extraction techniques and selective enrichment cultures. The techniques for the extraction of bacteria from decayed wood were assessed, compared and evaluated.; A large number of bacterial species were found associated with the exposed timbers. The majority of the species isolated showed lignocellulolytic abilities; a lesser number consisted of cellulolytic species whilst others were apparently not directly associated with wood decay but formed part of consortia involved in utilisation of wood cell wall components. All the timbers, irrespective of their lignin to cellulose contents or preservative treatment supported wood decaying bacteria. The isolated bacteria were identified to genus and species levels.; Bacteria were found to be the primary colonisers in seawater, riverwater and soil. Attachment was apparent after one weeks exposure and mediated by the production of various types of mucilage or exopolymeric materials. Several mechanisms were found involved in attachment processes and these are described. Attachment was followed by penetration of the wood cell walls which comprised strategies related to the types of bacteria rather than the timber species or prevailing environmental conditions.; Four types of wood decay were observed and examined and these are illustrated and described. The types include erosion, cavitation and two types of tunnelling. The two types of tunnelling are tunnelling Type I, characterised by the formation of chambered tunnels with cross walls and a new form of tunnelling described as tunnelling Type II. The inhibitory effects of CCA-treatment on bacterial wood decay were found to be negligible in the three environments.; The results presented are discussed in relationship to the importance of bacteria in the degradation of whole wood and breakdown of wood components in natural environments.