Bacterial wood degradation

Wooden foundation piles were traditionally used in Europe to improve the bearing capacity of water saturated soils along coastal areas and river sites for covering with buildings. Thus, many cities or rather districts, like Berlin, Amsterdam, Rotterdam, Haarlem, Stockholm, Venedig with many buildings of historic importance (German “Reichstag” in Berlin, parliament building in Stockholm, Rialto bridge in Venice, Hermitage in St Petersburg) are founded on wooden piles (Kretschmar et al. 2008a) Such wooden foundation piles are completely submerged in water saturated sediment or rather under the groundwater level. That means, they are stored in conditions where available oxygen is strongly reduced or even in anoxic conditions (Björdal 2000, Huismann et al. 2008a, b, Kretschmar et al. 2008b). Therefore this wood is well preserved against fungal degradation (Kohlmeyer and Kohlmeyer 1979). However, bacteria are able to colonize and degrade wood, until causing strength losses, in such oxygen reduced conditions. This process is a statically threat for the buildings supported by wooden foundations. It is also a special threat for archaeological wooden remains, stored in aquatic environments or wet soils. The degradation of archaeological wood stands for losses of information in research of our history. However, existing knowledge about the bacterial wood degradation process, like involved species and growth conditions, is insufficient. The main aims of this dissertation were to give an overview about published knowledge on wood degradation by bacteria (Part 1), characterisation of chemical changes in wood due to bacteria degradation (Part 2) and investigation of growth conditions of wood degrading bacteria in laboratory experiments (Part 3). With chemical analysis of wood attacked by bacteria possible indices to the enzymatic mechanism of the still unidentified bacteria should be shown. Furthermore, it should be investigated if chemical parameters can serve as bacterial wood decay detection methods. Wood samples, sampled within an European research project (BACPOLES), were investigated in lignin content, ash content, contents of mineral elements and content of carbohydrates including their composition. Additionally, technologies like Fourier-transformation-infraredspectroscopy (FTIR) and UV-microphotospectroscopy (UMSP) were used for chemical characterisation of wood degraded by bacteria. With laboratory experiments it was investigated: a) if the presence of oxygen is a prerequisite in the bacterial decay process, b) if elevated nitrogen concentrations due to eutrophication in the wood surroundings are favouring bacterial wood decay and c) if addition of sulphate to the sediment protect the wood against bacteria. In order to answer these questions three different microcosm (MC)-experiments were conducted (MC I – III).