Microbial biodeterioration of historic wood based on classical and omics methods with model studies

Abstract

The aim of this study was to identify microorganisms present in historic wooden objects stored in indoor and outdoor environments in Italy and Poland. A variety of methods, including culture methods, MALDI-TOF MS, and high-throughput sequencing, were used to identify microorganisms. Model studies were then conducted on oak wood samples under light and dark conditions, using single isolates from the tested samples and a mixed culture of isolated bacterial, mould, and algal strains. Changes in the samples were investigated by metabolomics analysis using UHPLC-MS/MS. Colour change was assessed in the CIELAB system. We also measured water absorptivity, pH levels, and degradation of cellulose and lignin. The most frequently isolated microorganisms were bacteria from the phyla Actinobacteria and Proteobacteria, particularly Actinomycetes, Cytophagales, Sphingomonadales, Burkholderia, Bacillus, Staphylococcus; fungi from the phyla Ascomycota and Basidiomycota, with genera including Cladosporium, Penicillium, Aspergillus Cladophialophora, and Pleurotheciella; green algae belonging to the phylum Chlorophyta, including the genera Chloroidium, Stichococcus, and Diplosphaerea. Model tests confirmed that these microorganisms are capable of altering the properties of wood, resulting in colour and pH changes, increased water absorption. Wood biodeterioration was found primarily to depend on the types of microorganisms present and on the light or dark conditions, which influenced the profiles of the metabolic pathways and the direction of the degradation process. Dark conditions favoured the growth of microorganisms on the wood and significantly increased water absorptivity, also contributed to yellowing, as confirmed by the production of β-carotene. Light conditions stimulated the activation of metabolic pathways related to photosynthesis, primary metabolism, and the TCA cycle. Although they did not favour the growth of microorganisms, light conditions triggered adaptive mechanisms, as evidenced by the production of more diverse and higher quantities of lipids in the microbial biofilms.