Abstract
This review provides information on the advances made leading to an understanding of the micromorphological patterns produced during microbial degradation of lignified cell walls of buried and waterlogged archaeological woods. This knowledge not only serves as an important diagnostic signature for identifying the type(s) of microbial attacks present in such woods but also aids in the development of targeted methods for more effective preservation/restoration of wooden objects of historical and cultural importance. In this review, an outline of the chemical and ultrastructural characteristics of wood cell walls is first presented, which serves as a base for understanding the relationship of these characteristics to microbial degradation of lignocellulosic cell walls. The micromorphological patterns of the three different types of microbial attacks—soft rot, bacterial tunnelling and bacterial erosion—reported to be present in waterlogged woods are described. Then, the relevance of understanding microbial decay patterns to the preservation of waterlogged archaeological wooden artifacts is discussed, with a final section proposing research areas for future exploration.
Highlights
In nature, wood can deteriorate from microbial attack
This and the observation that shipwrecks recovered from deep ocean sediments, where conditions can be anoxic, were found to be almost exclusively attacked by erosion bacteria (EB), suggest that the attack of Tunnelling bacteria (TB) on sunken ships is likely to have occurred prior to or during submergence of ships when the ocean water was sufficiently oxygenated to support the activity of TB, as these bacteria are considered to require oxygen for the degradation of lignocellulosic cell walls
Understanding the micromorphological pattern produced by TB during degradation of lignocellulosic cell walls is important in order to be able to recognise the presence/absence of bacterial tunnelling of cell walls in waterlogged archaeological woods
Summary
Wood can deteriorate from microbial attack. While this is important for the recycling of carbon stored in the wood cell wall, it is a cause of enormous economic losses due to the deterioration of wooden structures built for human use. Wood exposed to high moisture conditions is not generally attacked by basidiomycete fungi [2] owing to the saturation of wood tissues with water Under these conditions wood is not prevented from attack by soft-rot fungi and bacteria, for example, timbers placed in cooling towers and in retaining walls [3–5]. It is important to preserve or restore such valuable artefacts in a condition that can provide us with such information This requires detailed knowledge of the cause of their deterioration that may have occurred over prolonged exposure to anoxic conditions resulting from waterlogging, and the physical and chemical state of the excavated wooden objects [23]. This review will begin with a brief account of the chemical and ultrastructural characteristics of wood cell walls and a background of the micromorphological features associated with microbial degradation of lignocellulosic cell walls causing deterioration of buried and waterlogged archaeological woods before discussing the relevance of understanding decay patterns to the preservation of waterlogged archaeological wooden artefacts
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