Calcification processes in cyanobacteria-dominated pustular microbial mats in a high-altitude Andean lake (Catamarca, Argentina)

MLEWSKI, C; BOIDI, F.J.; GERARD, E.; GOMEZ, F.J.

Bergen

Congreso; Biosignatures Across Time and Space; 2014

Nordic Network of Astrobiology and the Centre of Geobiology at the University of Bergen

Calcification processes in cyanobacteria-dominated pustular microbial mats in a high-altitude Andean lake (Catamarca, Argentina) Mlewski, E.C.1, Boidi, F.J.1, Gerard E.2, and Gómez, F.1 1CICTERRA, Córdoba, Argentina 2IPGP, Institut de Physique du Globe de Paris (IPGP), Paris, France 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) where regional geology is dominated by andesitic to basaltic volcanic rocks with some rhyolite, dacite, and ignimbrites. High rates of evaporation result in mineral precipitation within an extensive microbial mat system. Carbonate deposits, typically calcite, consist of stromatolites, mega-oncoids, laminar carbonate crusts and micritic-peloidal sediments [1]. 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 [1]. This study is focused on the dark colored pustular microbial mats where filamentous cyanobacteria are abundant. These pustular 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. Better stratified pinkish to orange color microbial mats are more typically found subacueous and associated with more stable ponds. In these, pustular mats are only restricted to the pond edges or located on the exposed rims of carbonate microbialites growing inside these ponds. In order to record and understand calcification processes of microorganisms in these pustular mats, 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 microbial mats and carbonate microbialites samples. We also performed coupled CLSM and Raman spectroscopy on resin embedded microbialites to analyze the minerals surrounding the encrusted cells. Results show that the filamentous Cyanobacteria Rivularia is predominant (also we observed unidentified coccoid Cyanobacteria) (Fig 1). Rivularia can be encrusted by calcium carbonate (calcite) and can also be associated with sub-spherical aggregates several hundred microns in diameter. 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 (Fig. 1 B-E). Carbonate precipitation inside these aggregates is represented by nano-meter sized globular to spherical particles inside the EPS matrix [1]. Rivularia-like filaments have also been recorded growing encrusting carbonate microbialites rims and being incorporated during lamina accretion thus fossilized (Fig. 2 D). Ca and Mg ions have been observed by calcein staining fixed on the EPS sheats of Rivularia (Fig. 2B) together with calcite precipitation. It is still not clear if Rivularia filaments are active participants in the precipitation process or just passively entombed (Fig. 2A-D). Further studies are focused on understanding calcification processes of Rivularia in active microbial mats of Laguna Negra as well as their fossilized equivalent in the carbonate microbialites. This will allow us to better understand the geological record of Rivularia-like filaments in ancient examples [2,3].