Microbial aspects of hydroxylated polyamide's treatment on waterlogged archeological wood

When various agents alter the chemical structure of the main components waterlogged archeological wood (waw), consolidation treatments are needed. Biological attack may sometimes occur after consolidation treatments and it is related to the chemical characteristics of compounds, both synthetic (acrylic and vinylic resins, PEG) and natural (oils or shellac), with some compounds more likely to serve as carbon and energy sources for microbial growth. In order to obtain water soluble compounds with a high affinity for polar materials as wood, paper and natural fibres, several hydroxylated polyamydes have been synthesized and their application tested on waw (Cipriani et al. 2012. J Appl Polymer). Aim of this work was to evaluate the biostability of polyamides during the wood consolidation treatment in solution and their effect on the susceptibility to the microbial attack of the treated wood when air-exposed after the treatment. To test the biodegradation susceptibility of the consolidants, archeological wood samples were treated by immersion in a polyethylene-L-tartaramide solution. Microbial growth was monitored by the viable count method at the beginning and at the end (six weeks) of treatment. The viable count of the bacteria present in the consolidant solution was higher than in the control solution, nevertheless the presence of the commonly used biocide Preventol RI 80 was effective in completely controlling microbial growth until the end of the treatment. Bacteria isolated from the consolidant solution were grouped in few morphotypes, tested for their cellulolytic potential and identified by 16S rDNA analysis. To test the susceptibility to fungal attack of the treated wood, samples were preliminary conditioned at 20°C and RH 65% for 4 weeks and then incubated with cultures of Trametes versicolor on solid medium at 22°C and RH 70% for 16 weeks. Fungal growth was observed on the consolidant-treated wood as well as on the untreated control sample, but not in the samples consolidated in presence of the biocide. Our results suggest that tartaramydes are effective in consolidating archeological wood in a solution treatment. Even if they could be potentially degraded by microorganisms during the treatment and do not protect wood by microbial attack after treatment, the presence of a commonly used biocide during treatment is effective in avoiding microbial growth during and after the wood treatment.