Can microbes be used to preserve archaeological iron objects?

Can microbes be used to preserve archaeological iron objects? Lucrezia Comensolia, J. Maillardb, P. Juniera and E. Josepha,c a Laboratory of Microbiology, Institute of Biology University of Neuchâtel, Switzerland b Laboratory for Environmental Biotechnology, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland c Haute Ecole Arc Conservation-Restauration, Neuchâtel, Switzerland lucrezia.comensoli@unine.ch Without any conservation-restauration intervention archaeological iron objects are affected by a dramatic corrosion that leads to an irreversible loss of shape. The main issue with this metallic substrate is the chlorine content of the corrosion layers, which, by reaction with H2O and O2, causes an irreversible deterioration of the objects once excavated. Conservation-restauration technics available nowadays are ineffective, too expensive, time consuming and employ toxic substances. Therefore, the “MAIA” project (Microbe for Archaeological Iron Artworks) aims to develop new conservation-restauration methods based on microorganisms. For this purpose, iron reduction and chlorine uptake/volatilization capacities have been studied in selected microorganisms. These two metabolic abilities will allow to actively remove chlorine from the chlorinated iron compounds present in the corrosion layer and also to produce more stable iron minerals. For this aim, two anaerobic bacterial strains of Desulfitobacterium hafniense (strains LBE and TCE1, reported for dehalorespiration) and several fungal strains were studied. Different iron sources were tested either as soluble (iron citrate) or solid-phase iron compounds (powdered iron compounds from real archaeological artefacts). Spectrophotometric analyses were carried out to ascertain iron reduction and the evolution of the bacterial growth was quantified by quantitative Polymerase Chain Reaction (qPCR). Scanning Electronic Microscopy allows studying the fungal absorption of iron and chlorine, Raman Spectroscopy was used to identify the bio-mineral produced and finally we performed the first bacterial treatment of real archaeological iron objects. The results obtained show that microbes have the potential to stabilize iron objects by both reduction into more stable minerals and by removing chlorine from the object.