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The microbial epilithic communities associated with Uxmal Mayan stone monuments (Yucatan, Mexico) were preliminarily characterized by chemical and biochemical methods. The organic matter, organic carbon, and nitrogen content were within the respective ranges reported for other stone buildings, indicating that oligotrophic conditions prevailed at Uxmal's buildings. Quantitative differences in both total and phototrophic biomass were observed between stone and mortar (stucco) substrata, between indoor and outdoor locations, and between seasons. Microbial biomass and organic matter content were greater on indoor surfaces associated with more suitable microenvironmental conditions (availability of water and protection from direct sunlight) for microbial growth. Cyanobacterial photosynthesis, microbial debris, and bird droppings are the most probable sources of organic carbon and organic nitrogen in Uxmal's stone buildings. The epilithic communities appear to be dominated by phototrophs (mainly cyanobacteria) populations and associated bacteria. The latter are probably trophically dependent on the release of organic matter by photosynthetic production. These microbial biofilms and their activity may be responsible, in part, for the degradation of these stone monuments. [ABSTRACT FROM AUTHOR]

Chemical and biological weathering were studied on two historic churches in the city of Rio de Janeiro, Brazil. The churches exhibited contour scaling, granular disintegration and black crust development. High levels of SO 4 were found in façade stones of one church, São José, with significant levels of lead and copper. This suggests that vehicle emissions were important in stonework decay. Both gypsum and halite were detected, typical of buildings influenced by marine atmosphere and fuel-polluted environment. There was little bioweathering on this church, although the filamentous cyanobacterium Scytonema detected could be involved in black crust production. The other church (Nossa Senhora da Gloria) showed strong granular disintegration, with a green coloration on internal surfaces of some flakes removed for study. This church showed lower levels of geochemically important weathering compounds but was more colonized by fungi and cyanobacteria. The latter were shown by scanning electron microscopy to grow within the granitic gneiss stone and were probably involved in dissolution and redeposition of minerals. This church is rather far from the intense traffic of the centre of Rio de Janeiro and from Guanabara Bay, source of marine aerosols; it is located upon a green hill, where plant-associated fungi and cyanobacteria can readily gain access to the façade. The results of this study show the importance of local environment on the relative proportions of chemical and biological weathering of stone., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Cultural heritage monuments may be discolored and degraded by growth and activity of living organisms. Microorganisms form biofilms on surfaces of stone, with resulting aesthetic and structural damage. The organisms involved are bacteria (including actinomycetes and cyanobacteria), fungi, archaea, algae, and lichens. Interactions between these organisms and stone can enhance or retard the overall rate of degradation. Microorganisms within the stone structure (endoliths) also cause damage. They grow in cracks and pores and may bore into rocks. True endoliths, present within the rock, have been detected in calcareous and some siliceous stone monuments and are predominantly bacterial. The taxonomic groups differ from those found epilithically at the same sites. The nature of the stone substrate and the environmental conditions influence the extent of biofilm colonization and the biodeterioration processes. A critical review of work on microbial biofilms on buildings of historic interest, including recent innovations resulting from molecular biology, is presented and microbial activities causing degradation are discussed.

Buildings at the important archaeological sites of Uxmal and Kabah, Mexico, are being degraded by microbial biofilms. Phospholipid fatty acid (PLFA) and chlorophyll a analyses indicated that phototrophs were the major epilithic microorganisms and were more prevalent on interior walls than exterior walls. Culture and microscopical techniques showed that Xenococcus formed the major biomass on interior surfaces, but the stone-degrading genera Gloeocapsa and Synechocystis were also present in high numbers. Relatively few filamentous algae and cyanobacteria were detected. The fatty acid analysis also showed that complex biofilms colonize these buildings. Circular depressions observed by scanning electron microscopy (SEM) on stone and stucco surfaces beneath the biofilm corresponded in shape and size to coccoid cyanobacteria. SEM images also demonstrated the presence of calcareous deposits on some coccoid cells in the biofilm. Phototrophic biofilms may contribute to biodegradation by (1) providing nutrients that support growth of acid-producing fungi and bacteria and (2) active "boring" behavior, the solubilized calcium being reprecipitated as calcium carbonate.