Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Conservation method

Possible preservation or conservation strategies

The actual information on chemical-based preservatives is mainly related to fungal wood degradation, and their efficiency against bacterial degradation was never reliably proven. As it has to be used under water-saturated conditions, water-soluble non-fixating products are not suited. Moreover, a possible preservative should fit within the strict regulations for soil and groundwater minimum toxic levels. Therefore toxic water-soluble preservatives are not regarded as realistic to use against bacterial wood decay.

There are three promising approaches defined and each of them starts with a full description of the area to be treated. The site hydrology as well as the identification of the bacteria consortium, which causes bacterial degradation, is most important. Based on these inquiries specific mixtures of phages can be made. However field tests have to be carried out in order to get more knowledge whether a mono-phage-preservative should be used which is effective against the present bacteria consortium only, or whether it is possible to prepare a mixed-phage-preservative which is effective on a wider range of locations.

A second approach is related to the hydrology. It became clear that bacterial wood degradation is active only when there is a water flux in the wood. In order to create a static situation, either the hydrology can be manipulated or the wood structure can be closed by impregnation in the field. Probably a combination of both strategies is most efficient and could improve in addition the strength of the wood.

A third approach is based on a non-toxic active product, which affects the already weak competition position of wood degrading bacteria by promoting others. The result of this treatment should be that the number of wood degrading bacteria is diminished over longer time.

Future work and missing knowledge
Although populations of erosion bacteria in water-saturated wood make up a wide variety of species, the emergence of the CFB (Cytophaga-Flavobacterium-Bacteroides) group as an important component of the micro-flora requires further investigation for definite identities of pure cultures. Use of FISH (fluorescent in-situ hybridisation) techniques will pinpoint known bacterial types within a consortium. This will also provide a starting point for understanding the ecology and physiology of these bacteria. Particularly the conditions suitable for demonstrating attack on wood and kapok fibres, their carbon and nitrogen requirements, their respiration/fermentation and their response to different levels of oxygen, carbon dioxide and hydrogen sulphide, plus the effects of pH and temperature on their activity have to be further investigated. Such investigations will be tied to studies on cellulases, hemicellulases and ligninase enzymes produced by these bacteria in order to identify the optimum conditions for decay. At the same time the longevity and ecology of bacteriophages specific to isolated bacterial strains needs to be determined in natural environments.

One of the important results arising from the present work has been our improved understanding of water flow within wood. This has particular relevance to the movement of virus particles and bacterial cells in wood and raises questions about the need for a better understanding of the dynamics of water pressure in the ground, the permeability of different soil layers, the velocity of ground water flow and soil water analyses along the whole length of piles. This latter aspect of work to be done has special significance with respect to nitrogen availability and its importance in wood decay by erosion bacteria bearing in mind the limited amount of nitrogen naturally present in wood. Future work requires the establishment of field trials alongside laboratory experimentation. In the case of nitrogen, the use of 15N to monitor uptake into bacteria in laboratory microcosms and the use of radioactively spiked wood to monitor uptake are just two avenues of investigation. Physiological studies of this type will determine the value of changing environmental conditions in order to inhibit/control the activity of erosion bacteria by using for instance ‘lime-milk’ to increase pH. Similar studies using laboratory microcosms can also be set up under very low oxygen tensions to determine the effect on erosion bacterial activity, or to measure the effect of selected phages on bacteria artificially introduced into wood samples.

Reported by

Stichting Hout research
PO Box 497
NL 6700 AL Wageningen
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