Biological deterioration and biofilms on archaeological materials. An overview

PATRICIA S. GUIAMET.

Coimbra

Otro; IBBS 18 Meeting on New trends in Cultural Heritage Biodeterioration; 2018

Universidad de Coimbra

Biofilms affect the interaction between different materials and the environment not only in deleterious processes like biocorrosion, but also in several biological processes applied to materials of cultural heritage. When biofilms attach to these materials of social and cultural damage is irreparable and valuable information. Samples obtained from archaeological materials were analyzed by conventional microbiological techniques, molecular techniques and by different microscopic techniques. The use of microscopic techniques such as epifluorescence microscopy, stereomicroscopy (Olympus SZX7 trinocula) Scanning Electron Microscopy, Energy Dispersive X-ray, (SEM FEI-Quanta 200) with an EDS XFlash 6/30 microanalyzer(Bruker) and (iii) calcographic microscopy (Nikon Optiphot-Pol), and Confocal Scanning Laser Microscopy allows the examination of thick biological samples in four dimensions(x, y, z, time). Bacillus sp. showed considerable attack in the structure of the paper tested. Most of microorganisms tested degraded cellulose and produced pigments and acids(foxing). Pseudomonas aeruginosa strains isolated from archaeological textiles showed considerable evidence of attacking the textile structure. Biofilm formation and extracellular polymeric substances production by bacteria were demonstrated in laboratory assays. The SEM-EDAX technique showed a decrease to content of carbon in the areas of biofilm formation. Cyanolichens,fungi and bacteria have been isolated from archaeological ceramic. One strain of Pseudomonas sp. had the ability of bioadhesion and biofilm formation. On the other hand, SEM-EDAX of samples taken in the areas covered by cyanolichens showed high concentrati­ons of calcium leached from the ceramic by the action of carbonic and oxalic acids which would act as active chelating agents. Owing to the stereomicroscopy and SEM analysis,cyanolichens incrustations and pitting (0.5-1.5 mm) were observed on the edges and surfaces of ceramics. The growth of fungi and bacteria occurred in particular in cracks and micropits (0.1-2.0 mm), especially were organic matter was available. In conclusion, the deterioration of the different materials are mainly due to bacteria, fungi, cyanolichens, other microbiological contaminants and environmental pollutants.