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Appl Environ Microbiol. 2017 Apr 17;83(9). pii: e03478-16. doi: 10.1128/AEM.03478-16. Print 2017 May 1.

Use of Bacteria To Stabilize Archaeological Iron.

Author information

1
Laboratory of Microbiology, Institute of Biology, University of Neuchâtel, Neuchâtel, Switzerland.
2
Laboratory of Technologies for Heritage Materials, Institute of Chemistry, University of Neuchâtel, Neuchâtel, Switzerland.
3
Laboratory for Environmental Biotechnology, ENAC-IIE-LBE, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
4
Laboratory of Microbiology, Institute of Biology, University of Neuchâtel, Neuchâtel, Switzerland pilar.junier@unine.ch edith.joseph@unine.ch.
5
Laboratory of Technologies for Heritage Materials, Institute of Chemistry, University of Neuchâtel, Neuchâtel, Switzerland pilar.junier@unine.ch edith.joseph@unine.ch.
6
Haute Ecole Arc Conservation-Restauration, HES-SO, Neuchâtel, Switzerland.

Abstract

Iron artifacts are common among the findings of archaeological excavations. The corrosion layer formed on these objects requires stabilization after their recovery, without which the destruction of the item due to physicochemical damage is likely. Current technologies for stabilizing the corrosion layer are lengthy and generate hazardous waste products. Therefore, there is a pressing need for an alternative method for stabilizing the corrosion layer on iron objects. The aim of this study was to evaluate an alternative conservation-restoration method using bacteria. For this, anaerobic iron reduction leading to the formation of stable iron minerals in the presence of chlorine was investigated for two strains of Desulfitobacterium hafniense (strains TCE1 and LBE). Iron reduction was observed for soluble Fe(III) phases as well as for akaganeite, the most troublesome iron compound in the corrosion layer of archaeological iron objects. In terms of biogenic mineral production, differential efficiencies were observed in assays performed on corroded iron coupons. Strain TCE1 produced a homogeneous layer of vivianite covering 80% of the corroded surface, while on the coupons treated with strain LBE, only 10% of the surface was covered by the same mineral. Finally, an attempt to reduce iron on archaeological objects was performed with strain TCE1, which led to the formation of both biogenic vivianite and magnetite on the surface of the artifacts. These results demonstrate the potential of this biological treatment for stabilizing archaeological iron as a promising alternative to traditional conservation-restoration methods.IMPORTANCE Since the Iron Age, iron has been a fundamental material for the building of objects used in everyday life. However, due to its reactivity, iron can be easily corroded, and the physical stability of the object built is at risk. This is particularly true for archaeological objects on which a potentially unstable corrosion layer is formed during the time the object is buried. After excavation, changes in environmental conditions (e.g., higher oxygen concentration or lower humidity) alter the stability of the corrosion layer and can lead to the total destruction of the object. In this study, we demonstrate the feasibility of an innovative treatment based on bacterial iron reduction and biogenic mineral formation to stabilize the corrosion layer and protect these objects.

KEYWORDS:

Desulfitobacterium; akaganeite; biogenic minerals; iron reduction; vivianite

PMID:
28283522
PMCID:
PMC5394308
DOI:
10.1128/AEM.03478-16
[Indexed for MEDLINE]
Free PMC Article

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