Surfaces of buildings at the archaeological site of Palenque, Mexico, are colonized by cyanobacteria that form biofilms, which in turn cause aesthetic and structural damage. The structural characterization and species composition of biofilms from the walls of one of these buildings, El Palacio, are reported. The distribution of photosynthetic microorganisms in the biofilms, their relationship with the colonized substratum, and the three-dimensional structure of the biofilms were studied by image analysis. The differences between local seasonal microenvironments at the Palenque site, the bioreceptivity of stone and the relationship between biofilms and their substrata are described. The implications for the development and permanence of species capable of withstanding temporal heterogeneity in and on El Palacio, mainly due to alternating wet and dry seasons, are discussed. Knowledge on how different biofilms contribute to biodegradation or bioprotection of the substratum can be used to develop maintenance and conservation protocols for cultural heritage.

An aerophytic Nostoc, from a Mayan monument, has been characterized by phenotypic and molecular approaches, and identified as a morphospecies of Nostoc commune. Phylogenetic analysis indicates that it belongs to a Nostoc sensu stricto clade, which contains strains identified as N. commune. Nostoc cf. commune is found in two close areas: Site I (protected from direct sunlight by a wall), where it forms biofilms on mortar with Trentepohlia aurea; and Site II, where it grows on exposed stucco with the accompanying organism Scytonema guyanense. Over the year, in a habitat dictated by alternating wet and dry seasons, the organisms vary in appearance. Its life cycle comprises two seasonally-determined developmental stages (growth during the wet season and dormancy during the dry season) and two transitional stages (preparation for the dry season, and rehydration and recovery). At the beginning of the wet season the resistant stages from the previous dry season are rehydrated and form propagula, that adopt a colonial shape surrounded by a gelatinous sheath. As conditions become drier, clearly more in Site II, N. cf. commune employs adaptative strategies agains the drought, such as reducing the number of cells inside thick ensheathed colonies. Akinetes were observed, although only in Site II and in cultures of an isolated strain. Their fine structure shows parallel arrays of whorled thylakoids and septal intercellular connections. Spectral confocal laser scanning microscopy was used to analyze the fluorescence spectra of the photosynthetic pigments. N. cf. commune shows phycocyanin, allophycocyanin and chlorophyll a in both sites. Moreover, spectra of vegetative ensheathed cells, collected at Site II at the dry season, differed in their fluorescence spectrum: they feature a peak at 564 nm, attributed to phycoerythrin, which increases cell tolerance against the detrimental effects of strong light. These findings indicate that both the distribution and persistence of N. cf. commune might stem from cumulative adaptative strategies that increase its resistance to extreme desiccation.

This work characterizes a unicellular cyanobacterium with nearly spherical cells and thin-outlined sheaths that divide irregularly, forming small packets immersed in a diffluent mucilaginous layer. It was isolated growing on calcite speleothems and walls in a show cave in Collbató (Barcelona, Spain). Spectral confocal laser and transmission electron microscopy were used to describe the morphology, fine structure and thylakoid arrangement. The pigments identified were phycoerythrin, phycocyanin, allophycocyanin and chlorophyll a. Three-dimensional reconstructions, generated from natural fluorescence z-stacks, revealed a large surface area of nearly flat, arm-like thylakoidal membranes connected to each other and forming a unified structure in a way that, to our knowledge, has never been described before. Phylogenetic analyses using the 16S rRNA gene sequence showed 95 % similarity to strain Chroococcus sp.

The results obtained herein indicate that EtOAc extract of Streptomyces sp. has shown a strong antibacterial activity as well as moderate cytotoxic activity which make it a good candidate for metabolite isolation.