Phototrophic Biofilms on Ancient Mayan Buildings in Yucatan, Mexico Otto Ortega-Morales, 1 Jean Guezennec, 1 Guillermo Herna ´ndez-Duque, 2 Christine C. Gaylarde, 3 Peter M. Gaylarde 3 1 Laboratoire de Biochimie des Mole ´cules Marines, DRV/VP/BMM, IFREMER, B.P. 70, 29280, Plouzane ´, France 2 Facultad de Ingenierı ´a, Universidad del Mayab, Car. Me ´rida-Progreso km.15.5, Cordemex 97310, Me ´rida, Yucata ´n, Mexico 3 MIRCEN, Dept. Soils, UFRGS, Cx.P. 776, Porto Alegre, RS, 90001-970, Brazil Received: 15 March 1999 / Accepted: 24 June 1999 Abstract. 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. Microbial colonization of buildings causes aesthetic and physical damage to the structure through the formation of biofilms, which contain microorganisms and their meta- bolic products, such as extracellular polymeric materials (EPS), and both inorganic and organic acids. These polymers, principally polysaccharides, act as glues, trap- ping dirt and other particulate materials, increasing the disfiguring effects of the biofilm, and making the struc- ture more difficult to clean. This biodeterioration is especially important when the buildings are of historic and cultural interest. Uxmal, in the Yucatan Peninsula, is an important Mayan archaeological site, founded in 800 B.C. and consists of pyramids, temples, and other buildings. The extant buildings are of a Mayan architectural style called ‘‘Puuc,’’typical of sites in this area, and date from around 800–1000 A.D. Kabah is approximately 40 km southeast of Uxmal and has the same architectural characteristics, although it has been less restored. The buildings were made from local stone (limestone) and were originally coated with painted mortar (stucco), a mixture of burnt limestone, sand, and bark extracts [18]. Nowadays, most walls have lost their stucco coatings, leaving the bare rock exposed. Thick greenish and/or black biofilms are commonly associated with inner walls, while outer walls show biofilm growth only on wetter surfaces, such as cornices and crevices. Buildings can be colonized by bacteria, fungi, algae, and blue-green bacteria (cyanobacteria). The latter can survive repeated cycles of drying and rehydration, mak- ing them particularly important on exposed surfaces. Grant [13], in the UK, considered that cyanobacteria are of greater ecological importance as pioneer organisms than any other class. Danin and Caneva [6], working in the relatively dry environment of Jerusalem, suggested that blue-green bacteria were the most important influ- ence on the weathering of stone and rock. Colonization by these autotrophs is generally followed by the growth of heterotrophic organisms [20], and both groups can accelerate weathering. There is little information on the presence and role of microbial biofilms on stone buildings in subtropical climates. The goal of this work was to characterize the phototrophic biofilms at the archaeological sites of Ux- mal and Kabah in order to elucidate the microbial Correspondence to: O. Ortega-Morales CURRENT MICROBIOLOGY Vol. 40 (2000), pp. 81–85 DOI: 10.1007/s002849910015 An International Journal  Springer-Verlag New York Inc. 2000