Metabolic processes applied to endangered metal and wood heritage objects: Call a microbial plumber!

While often considered as harmful for cultural heritage, microorganisms can also be used for its safeguarding. The methods used so far for the conservation-restoration of cultural heritage are often unsatisfactory in terms of efficiency and durability. Inhibitors or complexing agents are also toxic and pose potential threats to human health and to the environment. Microbial-based technologies can provide sustainable solutions for heritage conservation-restoration using ecologically friendly biological treatments. Over the last decades, the development of biological methods and materials has become a significant alternative for the preservation of ancient heritage. Of particular note, microbial metabolisms are exploited to consolidate, clean, stabilize or even protect surfaces of cultural items. Taking advantage of unique properties of microorganisms, reactive corrosion products are extracted or converted into biogenic minerals that provide the treated surfaces with long-term stability. Examples of the techniques proposed include the formation of passivating biogenic layers that can be applied for preservation of metal-based heritage, as well as the development of methods for the preventative removal of iron species from waterlogged wood. This review presents the current advance made in research aiming to preserve copper- and iron-based artefacts, in particular sculptures but also archaeological objects, as well as in the development of a method for the extraction of iron species from waterlogged wood.