Lichen-like colonies of pure Trentepohlia on limestone monuments

Biofilms were collected on discoloured limestone samples and on adhesive tape from historic buildings at the Mayan site of Edzna, in Campeche, Mexico. Grey, brown, and black areas were colonised predominantly by coccoid and colonial cyanobacteria, also detected as endoliths. The major biomass on the pink stone surface was Trentepohlia. At low power, surface micropits containing crustose-lichen-like black colonies were seen within these pink areas. These were apparently pure colonies of T umbrina; no filamentous fungi were detected here. The black colour was produced by dense, amorphous pigment deposits in the colony centres. Insolation levels were high (similar to 400 mu mphotons m(-2) s(-1)) and the moisture content of the stone was 0.7%. The high carotenoid:chlorophyll-alpha ratio of Trentepohlia biofilms (3.9:1) is an adaptation protecting against environmental stress. Trentcpohlia caused severe local erosion (pitting) and, when present as a more uniform biofilm, the well-known pink surface discoloration. (c) 2006 Elsevier Ltd. All rights reserved.