Diversidad de bacterias y arqueas en tapete microbiano hipersalino: controles en microtexturas de carbonatos microbiales y señales biogeoquímicas

BOIDI, F.J.; GOMEZ, F.J.; MLEWSKI, C; FARIAS, M.E.

CORDOBA

Congreso; XI SAMIGE (Congreso Argentino de Microbiología General).; 2015

XI SAMIGE (Congreso Argentino de Microbiología General).

Microbial mats are laminated microbial communities typically developed in extreme environments. Their stratified appearance isdue to vertical segregation of microorganisms in response to mm-scale gradients of light and redox potential. Laguna Negra, inthe Puna region of Argentina is a high-altitude hypersaline lake under extreme environmental conditions (high UV-radiation,extreme temperatures and salinity), which harbors an extensive microbialitic system. It consists of carbonate microbialites,morphologically diverse microbial mats and mineral precipitation within them. Here we studied the microbial mat that prevails inthe system, developing under shallow water (up to 10 cm). We recognized an orange-pink top layer, followed by purple andgreen layers in the undermat and underlain by a dark-colored horizon at the bottom. We explored bacterial and archaealdiversity in each strata using 16S rDNA pyrosequencing and related this information with carbonate microtextures and isotopicrecord reported there. The top layer revealed Bacteroidetes, Proteobacteria, Verrucomicrobia and DeinococcusThermus asprominent phyla. Cyanobacteria is four times more abundant in the upper layer than deeper in the mat, even though is not oneof the most abundant phylum. Diatoms are common as seen under de SEM and optical microscopy. Members of these groupshave photosynthetic lifestyle and resist high UV radiation, which is expected near the surface and given the high UV light influxreported in the area. The second layer presented anoxigenic phototrophs: abundant Chloroflexi, mainly the Chloroflexia class,and the highest proportion of Gammaproteobacteria, enclosing sulfur oxidizing bacteria. Third green layer contained the highestproportion of sulfur reducing Deltaproteobacteria. Certain groups increased their presence deeper in the mat, at the dark bottom,such as Firmicutes and Archaea (mostly Euryarchaeota). The order Halanaerobiales prevailed within Firmicutes, comprisingfermentative halophilic anaerobes. Euryarchaeota includes methanogenic extremophiles, likely to occur in the anoxic strata ofthe mat. Previous work showed that Ca-carbonate precipitation (typically calcite) is associated with exopolymeric substancessegregated by microorganisms. In addition, aragonite has been observed closely related to cyanobacteria and diatomssuggesting some microbial control. C-O isotopes (within carbonates and organic matter) and S-isotopes (carbonate associatedsulfates and pyrite) suggest a complex combination of physicochemical (evaporation, degasification) and biological processes(photosinthesis, methanogenesis, sulfate reduction, sulfur oxidation) controlling the isotope signature. The 16S rDNA dataindicate the presence of organisms with these metabolisms. Further studies (e.g. metagenomics, culturing) will allow us tounravel the specific role of physicochemical and microbiological controls within the carbonates and its biogeochemicalsignatures.