Microbial diversity and carbonate micro-textures in diatom-rich microbial mats in a high-altitude hypersaline lake in Catamarca (Argentina)

BOIDI, FLAVIA; GOMEZ, FERNANDO; MLEWSKI, CECILIA; FARÍAS, MARÍA EUGENIA

Bergen

Congreso; Biosignatures Across Time and Space; 2014

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

Microbial diversity and carbonate micro-textures in diatom-rich microbial mats in a high-altitude hypersaline lake in Catamarca (Argentina) Boidi Flavia Jaquelina1,2, Gomez Fernando Javier2, Mlewski Cecilia2 and Farías María Eugenia1 1Planta Piloto de Procesos Industriales Microbiológicos- CONICET, San Miguel de Tucumán, Argentina 2Centro de Investigaciones en Ciencias de la Tierra- CONICET, Córdoba, Argentina Microbial activity leaves fingerprints in the sedimentary record by catalysing reactions through enzymatic activity, recycling dissolved chemical species, producing geochemical gradients, and triggering precipitation and dissolution of certain minerals. Thus, microbiological influence on mineral precipitation (e.g. carbonates) can produce changes in mineralogy, crystal fabrics and elemental chemistry and those changes can potentially be recognized in the sedimentary record. Understanding these processes in modern environments can be useful to better understand the geological record. Here we show new data of microbial mats and biofilms recorded in a high-altitude (4600 masl) hypersaline lake known as the Laguna Negra, in Catamarca (Argentina). This lake is characterized by extreme environmental conditions such as high UV radiation, high thermal amplitude, dryness and salinity, features that act as natural selective pressure only allowing the development of microbial life adapted to these conditions. Along the south margin of the lake an extensive and heterogeneous microbial mat system is associated with microbialites (mega-oncoids, mini-stromatolites and laminar crusts) [1]. In this study we analyzed microbial diversity to recognize the main bacterial groups present in the Laguna Negra microbial mats in order to evaluate their potential influence on carbonate precipitation. To achieve this we performed 16S rDNA pyrosequencing, pigment composition analysis and microtextural analysis of different microbial mats sites as well as a detailed macro and micro-textures study of associated carbonate microbialites. Most environmental sequences obtained from Laguna Negra microbial mats were affiliated to Proteobacteria, Verrucomicrobia, Bacteroidetes, Thermi, and to a lesser extent, Spirochaetes and Firmicutes. Between the bacterial groups here recorded, and those are known to have some impact on carbonate precipitation, we can mention abundant Cyanobacteria (in site LN5), Gammaproteobacteria, (particularly in site LN4), sulphate reducers such as Deltaproteobacteria (sites LN4 and LN2R) and Firmicutes (site LN2N). Pigments analysis revealed the presence of UV absorbing compounds, chlorophyll a, bacteriochlorophyll a and c in the mats, and elemental sulphur, implying the occurrence of phototrophic metabolisms and supporting the 16S rDNA diversity analysis. A commonly observed feature in the Laguna Negra microbial mats and biofilms has been the presence of sub-spherical aggregates composed by diatoms and bacteria, immersed in exopolymeric substances EPS), where precipitation of nano-globular carbonates is typically observed. This has also been recorded preserved in micritic, whitish granular lamina in the microbialites associated with these mats. Some bacterial taxonomic groups here recorded are also particularly known to associate with diatoms [2]. Within these bacteria we reported Bacteroidetes (Maribacter sp., Winogradskyella sp., Polaribacter sp. as closest relatives), Alphaproteobacteria (Hyphomonas sp., Rhodovulum sp.), Gammaproteobacteria (Glaciecola sp., Marinobacter sp., Halomonas sp., Pseudoalteromonas sp.), and Firmicutes (Bacillus sp.) suggesting that the interactions between diatoms and bacteria can have an effect on calcification processes and microbialite formation in Laguna Negra. Although aggregation of diatoms with bacteria and organic polymers is commonly observed in the ocean during diatom blooming events, it is not clear yet the origin of the Laguna Negra aggregates and its relationship with carbonate precipitation. Diatoms are known to produce significant amounts of exopolymeric substances, largely composed of polysaccharides and bacteria (for example sulfate reducing bacteria) can oxidize these as a nutrient and energy sources. In addition, some diatoms produce EPS that promote the growth of specific taxa of bacteria [2] suggesting more specific interactions. It is possible that carbonate precipitation inside the Laguna Negra aggregates could be related to interactions between diatoms and bacteria, including the bacterial groups that are known to promote precipitation. The capacity of EPS to fix cations like Ca2+ and EPS degradation by heterotrophic bacteria could trigger carbonate precipitation, for example by the activity of sulfate reducing bacteria which are abundant in the Laguna Negra mats. In addition, purple sulfur bacteria have been here recorded and it has been suggested that these can trigger carbonate precipitation as well [3]. Ongoing studies are focused on understanding this microbial diversity, specific metabolisms and its potential impact on carbonate precipitation.