Microbial diversity and calcification processes of Pustular microbialites in a high-altitude andean lake (Catamarca, Argentina)

MLEWSKI, EC; BOIDI, FJ; GERARD, E; GÓMEZ, F

Mar del Plata

Congreso; X Congreso de Microbiología General; 2014

SAMIGE

MICROBIAL DIVERSITY AND CALCIFICATION PROCESSES IN A PUSTULAR MICROBIAL MAT IN A HIGH-ALTITUDE ANDEAN LAKE (CATAMARCA, ARGENTINA) Estela C Mlewski1 , Flavia J Boidi1 , Emanuelle Gérard2 , Fernando Gómez1 . 1 Centro de Investigaciones en Ciencias de la Tierra CICTERRA. 2 Institut de Physique du Globe de Paris IPGP. cmlewski@gmail.com Laguna Negra, in the Puna region of Argentina is a high-altitude hypersaline lake with extreme environmental conditions (high UV-radiation, temperature extremes, and salinity). High rates of evaporation result in mineral precipitation within an extensive microbial mat system. Microbial mats in the Laguna Negra display a variety of stratiform, pustular, and pinnacle morphologies. Biofilms are also present, coating both the subaqueous sedimentary substrate and mineralized components. This study is focused on the dark colored pustular microbial mats. These mats are usually located in areas where the substrate is partially exposed, growing close to the air-water interface or partially subaerial, where desiccation and a high UV radiation influx are common. In order to record and understand calcification processes, we analyzed microbialites and microbial mats samples with epifluorecent microscopy, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) in fresh and resin embedded samples. In addition we analyzed microbial diversity to recognize the main bacterial groups present in this site in order to evaluate their potential influence on carbonate precipitation. To achieve this we performed 16S rDNA pyrosequencing. Most of the environmental sequences obtained were affiliated to Proteobacteria, Verrucomicrobia, Bacteroidetes, Thermi, Cyanobacteria and to a lesser extent, Spirochaetes and Firmicutes. Between the bacterial groups here recorded, and those that are known to have some impact on carbonate precipitation, we can mention abundant Cyanobacteria and specially the filamentous Cyanobacteria Rivularia whichis predominant. Rivularia can be encrusted by calcium carbonate (calcite) and can also be associated with subspherical aggregates. These aggregates are composed of Cyanobacteria and Diatoms (Achnanthes brevipes, Halamphora, Navicula, Surirella Striatula, etc), together with other bacterial groups, and are usually embedded in exopolymeric substances (EPS) where carbonate precipitation also takes place. Carbonate precipitation inside these aggregates is represented by nano-meter sized globular to spherical particles inside the EPS matrix. It is still not clear if Rivularia filaments are active participants in the precipitation process or just passively entombed. Ongoing studies are focused on understanding this microbial diversity, specific metabolisms in active microbial mats, with an special focus on Rivularia Cyanobacteria and its potential impact on carbonate precipitation. This will allow us to better understand the geological record of Rivularia-like filaments in ancient examples.