In situ evaluation of the biodeteriorating action of microorganisms and the effects of biocides on carbonate rock of the Jeronimos Monastery (Lisbon)

Abstract

The biodeterioration effects of microorganisms colonizing the cloister terrace wall of the Jeronimos Monastery (Lisbon) were evaluated using several microscopy techniques that allow the in situ examination of lithobiontic communities. The techniques applied were: scanning electron microscopy with back-scattered electron imaging (SEM-BSE), low temperature scanning electron microscopy (LTSEM), transmission electron microscopy (TEM) and an X-ray energy dispersive spectroscopy (EDS) microanalytical system. The stone was seen to be colonized by different lichens and microorganisms and lichen thalli of Thyrea, Aspicilia, Verrucaria and Caloplaca were identified. Cyanobacteria were frequently observed close-by, as single cells or colonies and heterotrophic bacteria were also found among these. The lithobiontic community showed biogeophysical and biogeochemical effects on the substrate. Cyanobacteria produced bowl- or pear-shaped cavities. Using SEM-BSE and TEM we were able to observe a mineral network structure adjacent to the cyanobacterial wall that might be related to calcium biomobilization processes. Neoformation of biogenic carbonate was detected in thalli of the lichen Thyrea. This information was complemented by observing details of the response of these biological components to the biocidal agents, ALGOPHASE ®, METATIN ® and PREVENTOL R80 ®. After treatment, Thyrea remained on the stone, although ultrastructural alterations were observed in the photobiont. When the effects of the biocides on the ultrastructure of the cyanobacteria were analyzed, ALGOPHASE ® proved to be the least efficient, while PREVENTOL R80 ® led to the complete disorganization of the prokaryotic cyanobacterial cell. These results point to the importance of evaluating biodeterioration processes and possible treatment measures without extracting the microorganisms from their microhabitat.