Soil and rock surfaces support microbial communities involved in mineral weathering processes. Using selective isolation, fungi were obtained from limestone surfaces of Mayan monuments in the semi-arid climate at Yucatan, Mexico. A total of 101 isolates representing 53 different taxa were studied. Common fungi such as Fusarium, Pestalotiopsis, Trichoderma and Penicillium were associated with surfaces and were, probably derived from airborne spores. In contrast, unusual fungi such as Rosellinia, Annulohypoxylon, and Xylaria were predominantly identified from mycelium particles of biofilm biomass. Simulating oligotrophic conditions, agar amended with CaCO3 was inoculated with fungi to test for carbonate activity. A substantial proportion of fungi, in particular those isolated from mycelium (59%), were capable of solubilizing calcium by means of organic acid release, notably oxalic acid as evidenced by ion chromatography. Contrary to our hypothesis, nutrient level was not a variable influencing the CaCO3 solubilization ability among isolates. Particularly active fungi (Annulohypoxylon stygium, Penicillium oxalicum and Rosellinia sp.) were selected as models for bioweathering experiments with limestone-containing mesocosms to identify if other mineral phases, in addition to oxalates, were linked to bioweathering processes. Fungal biofilms were seen heavily covering the stone surface, while a biomineralized front was also observed at the stone-biofilm interface, where network of hyphae and mycogenic crystals was observed. X-ray diffraction analysis (XRD) identified calcite as the main phase, along with whewellite and wedellite. In addition, lower levels of citrate were detected by Attenuated Total Reflectance-Fourier-Transform Infrared Spectroscopy (ATR-FTIR). Overall, our results suggest that a diverse fungal community is associated with limestone surfaces insemi-arid climates. A subset of this community is geochemically active, excreting organic acids under quasi-oligotrophic conditions, suggesting that the high metabolic cost of exuding organic acids beneficial under nutrient limitation. Oxalic acid release may deteriorate or stabilize limestone surfaces, depending on microclimatic dynamics.

Biofilms colonizing ancient limestone Mayan monuments in Uxmal (Yucatán, Mexico) were characterized for their microbial composition and differences using phospholipid fatty acid (PLFA) analysis and single-strand conformation polymorphism (SSCP) of polymerase chain reaction (PCR)-amplified genes of the rRNA small subunit. Biofilms 1–7, displaying different macroscopic characteristics, were drawn from interior and exterior limestone walls, which were characterized by different microenvironmental conditions. Inner surfaces that were exposed to low light intensity and higher water availability supported a higher biofilm biomass, probably indicating that these environmental conditions are more suitable for biofilm growth and development. Sequencing of SSCP profiles from the biofilms showed that bacteria affiliated with the phyla Proteobacteria, Bacteroidetes and Cyanobacteria colonized both internal and external surfaces, although certain Nevskia and Salinibacter were particularly associated with internal biofilms. In contrast, a particular biofilm community composed almost exclusively of Rubrobacter-related bacteria was found in only one exterior partially shaded sample (biofilm 3), characterized by high illumination and low water content. No specific organisms were detected in biofilm 7. The PLFA profiles suggested that cyanobacteria were the biomass-dominant group in most biofilms, except for biofilm 3 (exterior) where actinobacterial markers were detected in significant proportions. Interestingly, most of the detected sequences were related to halophylic bacteria, although the similarity of these clones to known sequences in databases was low (< 94%). This finding suggests that much bacterial novelty, probably of halophylic nature, remains to be identified in these biofilms. Our study suggests that water availability and light regime appear to be the main environmental determinants defining boundaries for biofilm formation, while substratum salinity appears to be an important abiotic factor that influences biofilm community structure in these specialized microbial habitats.

Agave plants are a valuable source of raw material due to its fibrous and complex sugar content of their leaves and core, and their bagasse waste can be use for several aims. This plant genus belongs to the Agavaceae family and until now more than 200 species have been described. A large number of Agave species are currently used as raw material in several biotechnological processes. This review shows the reported applications and patents on fields like alcoholic brewages with special reference to Tequila and Mezcal, the isolation and use of compounds such as saponins and agave fructans, and their potential biotechnological application on several human demands. The process to obtain fibers and cellulose, stock feeds, and several miscellaneous extractives are also reviewed. Some possibilities and problems of cultivation are discussed.

Carotenoid cleavage dioxygenases (CCDs) are a class of enzymes involved in the biosynthesis of a broad diversity of secondary metabolites known as apocarotenoids. In plants, CCDs are part of a genetic family with members which cleave specific double bonds of carotenoid molecules. CCDs are involved in the production of diverse and important metabolites such as vitamin A and abscisic acid (ABA). Bixa orellana L. is the main source of the natural pigment annatto or bixin, an apocarotenoid accumulated in large quantities in its seeds. Bixin biosynthesis has been studied and the involvement of a CCD has been confirmed in vitro. However, the CCD genes involved in the biosynthesis of the wide variety of apocarotenoids found in this plant have not been well documented. In this study, a new CCD1 gene member (BoCCD1) was identified and its expression was charaterized in different plant tissues of B. orellana plantlets and adult plants. The BoCCD1 sequence showed high homology with plant CCD1s involved mainly in the cleavage of carotenoids in several sites to generate multiple apocarotenoid products. Here, the expression profiles of the BoCCD1 gene were analysed and discussed in relation to total carotenoids and other important apocarotenoids such as bixin.