Cyanobacteria cause black staining of the National Museum of the American Indian Building, Washington, DC, USA.

Microbial deterioration of stone is a widely recognised problem affecting monuments and buildings all over the world. In this paper, dark-coloured staining, putatively attributed to microorganisms, on areas of the National Museum of the American Indian Building, Washington, DC, USA, were studied. Observations by optical and electron microscopy of surfaces and cross sections of limestone indicated that biofilms, which penetrated up to a maximum depth of about 1 mm, were mainly composed of cyanobacteria, with the predominance of Gloeocapsa and Lyngbya. Denaturing gradient gel electrophoresis analysis revealed that the microbial community also included eukaryotic algae (Trebouxiophyceae) and fungi (Ascomycota), along with a consortium of bacteria. Energy-dispersive X-ray spectroscopy analysis showed the same elemental composition in stained and unstained areas of the samples, indicating that the discolouration was not due to abiotic chemical changes within the stone. The dark pigmentation of the stone was correlated with the high content of scytonemin, which was found in all samples.

Microbial deterioration of artistic tiles from the façade of the Grande Albergo Ausonia & Hungaria (Venice, Italy).

The Grande Albergo Ausonia & Hungaria (Venice Lido, Italy) has an Art Nouveau polychrome ceramic coating on its façade, which was restored in 2007. Soon after the conservation treatment, many tiles of the façade decoration showed coloured alterations putatively attributed to the presence of microbial communities. To confirm the presence of the biological deposit and the stratigraphy of the Hungaria tiles, stereomicroscope, optical and environmental scanning electron microscope observations were made. The characterisation of the microbial community was performed using a PCR-DGGE approach. This study reported the first use of a culture-independent approach to identify the total community present in biodeteriorated artistic tiles. The case study examined here reveals that the coloured alterations on the tiles were mainly due to the presence of cryptoendolithic cyanobacteria. In addition, we proved that the microflora present on the tiles was generally greatly influenced by the environment of the Hungaria hotel. We found several microorganisms related to the alkaline environment, which is in the range of the tile pH, and related to the aquatic environment, the presence of the acrylic resin Paraloid B72® used during the 2007 treatment and the pollutants of the Venice lagoon.

Monitoring lichen recolonization on a restored calcareous statue.

Monitoring lichens on monuments can have different purposes, one of which is monitoring the effectiveness of restoration. In the present work, lichen recolonization on a calcareous statue was monitored for evaluating the long-term effectiveness of restoration in preventing new biological growth. Species richness and composition of lichen communities from three surveys (one pre-restoration and two post-restoration) covering a twelve years period, are compared. The long-term effectiveness of the restoration of the statue was low, and even the use of water repellents failed in avoiding lichen recolonization. The short durability of the treatment applied to the statue was also confirmed by the recolonization pattern which seemed more related to the geometry of the statue than to the hydrorepellence of its surface. Recolonization involved lichen communities which differed from those covering the statue before restoration. Some species were significantly associated with each step of the succession, as well as to pre-restoration conditions. The pre-restoration lichen community was more differentiated across the statue, indicating a complex "Statue Ecosystem" that is perhaps more typical of a later successional stage. On the contrary, only a few communities dominated by a few species were involved in the recolonization. The management of stoneworks exposed in the parks of villas could be more effective focusing on maintenance than on repeated cleaning or restoration, whose effects are hindered by practical difficulties in preventing the causes of biological growth. If restorations are not going to be maintained, it would be better to retain a more historic, diverse, and complex lichen community than a simplified community of "weedy" lichens that quickly cover almost the same area as the pre-restoration community did. With this perspective, in the environmental and artistic context of these parks, biodiversity should be included in the concept of the historic and artistic value of the artworks.