Bacterial and fungal diversity and biodeterioration problems in mural painting environments of St. Martins church (Greene–Kreiensen, Germany)

Abstract

Microbial biofilms were massively developing on the surfaces and within the painting layers of mural paintings of a parish church in Lower Saxony, which were exposed and restored in the end of 1970s. The causes of the heavy infections remained unclear. Within the frame of an European research project (ENV4-CT98-0705) these microbial infections were documented and analyzed. By scanning electron microscopy (SEM) and dissecting microscope analysis of mural painting fragments it was shown that the main biofilm formers were microscopic fungi with strong pigment development. Thirty-two fungal and 139 heterotrophic bacterial isolates were obtained by cultivation methods. Most of the fungi (32 isolates) were characterized by morphological methods and nutritional physiology (BIOLOG system) and identified as Acremonium, Aspergillus, Cladosporium, Fusarium and other imperfect fungal genera among which several melanized Mycelia sterilia. Representative bacterial strains were analyzed by 16S rDNA sequencing, the majority of bacteria belonged to the genera Arthrobacter, Bacillus and Bacillus-related genera. Isolated strains (both fungal and bacterial) belong to spore formers and thus could have been potentially stimulated to grow only by the transfer to the growth medium. The results of SEM analysis, cultivation experiments and visualization of microbial activity, confirm the hypothesis that the current microbial community is inactive and represent a stagnant microbial community developed after drastic environmental changes caused by an unfortunate conservation treatment.