Characterisation of microbial attack on archaeological bone
Introduction
Bone is used extensively as a source of information in archaeological research as it is usually the only animal or human tissue preserved, though often it is altered or destroyed as well. With the development of biomolecular analysis, the significance of understanding bone preservation has increased. One of the earliest types of alteration is microbial attack. Yoshino et al. [42]observed evidence of microbial alteration in bone 5 years post-mortem, indeed Haversian canals were (still) filled with bacteria. Bell et al. [5]found evidence of microbial attack in bone in a forensic study, as soon as 3 months post mortem, though this sample was recovered from a predator scat.
Biological alteration in bone is in most cases caused by fungi [31], bacteria [2], [14], [23], or cyanobacteria in marine environments [4]. Wedl first described microbial attack on mineralised tissue in 1864, finding tunnels of approximately 8 μm in diameter in sections of teeth exposed to untreated well water and in fossil reptile teeth. This type of tunnelling is defined as Wedl or centrifugal tunnelling by Hackett [14]. These tunnels range in diameter from 5 to 10 μm and under electron microscopy [31]appear empty with well-defined calcified walls, implying that collagen and mineral are both resorbed by the fungi.
Three types of microscopical focal destruction (mfd)—described by Hackett as ‘linear longitudinal’, ‘budded’ and ‘lamellate’—are generally assumed to be caused by bacteria. These mfd can be distinguished histologically by morphology; size, shape, the presence of a hypermineralised rim and the presence of a lamellate content. Under light microscopy these mfd show a granulous or fibrillar content, but higher magnification shows that their interior actually consists of small pores [2], [23], [40]. Mercury intrusion porosimetry (HgIP) shows an increased volume in pores with diameters in the 0.1–10 μm region, with the largest increase observed at approximately 0.6 and 1.2 μm [35], [40], consistent with the average diameter for bacteria (0.5 μm [18]). Indeed, Baud and Lacotte [2]argue that the small pores that are visible at electron microscope level are the mineralised remains of bacteria, in which case they would not form the interconnected porosity observed by Turner-Walker et al. [40].
We report here some results from a European study, which attempted to identify the key contributory factors to bone deterioration. Biological alteration of archaeological bone is a widespread phenomenon apparently not limited to a single burial environment [21]. Its effect on bone preservation is important as it can accelerate degradation by increasing the bone porosity [35]and simultaneously reduces chances of success for biomolecular research through loss or contamination of target molecules [9]. Two methodological approaches, mercury intrusion porosimetry (HgIP) and histology, are combined for the first time in this project. While histology has been widely used previously to characterise microbial attack (e.g. [3], [11], [14]), HgIP makes it possible to analyse a larger sample of bone and provides quantitative results [40].
Section snippets
Materials and methods
Samples of animal and human bone and related soil were taken from excavations in Sweden, theNetherlands, the United Kingdom, Italy and Turkey, spanning four climatic regimes (Mediterranean, Continental, Maritime (coastal) and Subarctic) (Appendix A). The 41 sites were chosen on the basis of well-defined geological and archaeological context and documented environmental parameters such as ground water table, annual rainfall and land use history. Sites ranged from the Neolithic to early modern
Characterisation of microbial attack
Two hundred and sixty-one bone samples from 41 different archaeological sites were analysed using histology and 233 samples of these using mercury intrusion porosimetry as well. Of the samples analysed histologically (n=261), 177 samples showed microbial attack (68%). Only 9% of the total sample could be considered well preserved. In 12% of the bones the characteristic ‘Apigliano style degradation’ [38]could be observed. Apigliano style degradation is characterised by highly crystalline and
Discussion
In this study we used the combination of histology and mercury intrusion porosimetry to characterise microbial attack. The porosity traces of all types of bacterial tunnelling showed a double peak, with increases in the pore volume at about 0.6 μm and 1.2 μm; albeit the former was smaller in the lamellate tunnelling (0.3 μm). Most bones with lamellate tunnels were found on very similar sites (large, densely occupied, medieval cemeteries). The smaller pores may therefore reflect differences in
Conclusion
Microbial attack is an important contributor to bone deterioration. HgIP and histology can be used to detect its effects. While HgIP analyses a larger sample volume and gives quantitative results, histology is needed to distinguish between bacterial and fungal attack. Bone from complete burials (animal and human) is more likely to be affected by bacterial attack indicating that bacterial degradation is linked to putrefaction and the very early stages of degradation. The majority of bone, which
Acknowledgements
This project has been carried out with financial support of the European Union, Directorate General No. XII, in the framework of the Environment and Climate programme (1994–1998), project no. ENV4-CT98-0712. Prof. John N. S. Matthews (University of Newcastle) is gratefully acknowledged for his help with the statistical analysis. Two anonymous reviewers are thanked for their valuable comments.
References (43)
Paleopathology and diagenesis; a SEM evaluation of structural changes using backscattered electron imaging
Journal of Archaeological Science
(1990)- et al.
The speed of post mortem change to the human skeleton and its taphonomic significance
Forensic Science International
(1996) - et al.
Microbially-induced promotion of amino acid racemization in bone: isolation of the microorganisms and the detection of their enzymes
Journal of Archaeological Science
(1993) Towards an understanding of the microbial decomposition of archaeological bone in the burial environment
Journal of Archaeological Science
(1995)- et al.
Histomorphological alteration in buried human bone from the lower Illinois Valley: implications for paleodietary research
Journal of Archaeological Science
(1987) - et al.
Bones and ground water: towards the modelling of diagenetic processes
Journal of Archaeological Science
(1995) - et al.
Measurements and relationships of diagenetic alteration of bone from three archaeological sites
Journal of Archaeological Science
(1995) Bone degradation in a compost heap
Journal of Archaeological Science
(1998)- et al.
An evaluation of nitrogen porosimetry as a technique for predicting taphonomic durability in animal bone
Journal of Archaeological Science
(2003) - et al.
Detection of bone preservation in archaeological and fossil samples
Applied Geochemistry
(1989)
Some 320-year-old soft tissue preserved by the presence of mercury
Journal of Archaeological Science
Microscopical study on time since death in skeletal remains
Forensic Science International
In vitro decomposition of bone collagen by soil bacteria: the implications for stable isotope analysis in archaeometry
Archaeometry
Etude au microscope électronique à transmission de la colonisation bactérienne de l'os mort
Comptes rendu de l'Académie des Sciences
Diagenetic alteration to teeth in situ illustrated by backscattered electron imaging
Scanning
The Fungi
The preservation of ancient DNA and bone diagenesis
Ancient Biomolecules
A histological study of archaeological bone decomposition
A study of the decay processes of human skeletal remains from the parish church of the Holy Trinity, Rothwell, Northamptonshire
Oxford Journal of Archaeology
Chemical and ultrastructural aspects of decomposition
Identification of medieval human soft tissue remains in an advanced state of decomposition
Biotechnic & Histochemistry
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