Topochemical and transmission electron microscopic studies of bacterial decay in pine (Pinus sylvestris L.) harbour foundation piles

Bacterial degradation of Pinus sylvestris harbour foundation piles was studied topochemically by scanning UV-microspectrophotometry. This analytical technique enables direct imaging of lignin distribution within individual cell wall layers. Additionally, light and transmission electron microscopy (TEM) was used to characterise structural changes of the cell walls. Various decay stages were found in the samples. TEM revealed that the bacterial degradation occurred mainly in the S2, leaving granular remnants in degraded wall portions with lower as well as higher electron density than the surrounding unmodified wall. In the initial stages, topochemical investigations revealed that lignin modification starts in the innermost parts of the secondary wall, most clearly observed in latewood tracheids. During advanced degradation, lignin modification occurs more or less severe in walls of all cell types. However, even in cell portions with intensive decay, the compound middle lamellae and ray tracheids were undegraded. The knowledge about lignin modification at initial stages of wood degradation by bacteria is of fundamental importance to provide more information on the process of cell wall decay.