Elemental composition of extant microbialites: mineral and microbial carbon

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Luisa I Falcón1, Patricia M Valdespino-Castillo1, Hoi-ying N Holman2, Martin Merino-Ibarra3, Mariana García-Guzmán1,4, Luz M López-Gómez3, Jesús Martínez1, Rocio J Alcantara-Hernandez5, Yislem Beltran4, Carla Centeno6, Daniel Cerqueda García1,4, Teresa Pi-Puig7 and F. Sergio Castillo3, (1)UNAM National Autonomous University of Mexico, Instituto de Ecología, Mexico City, Mexico, (2)Lawrence Berkeley National Lab, Berkeley, CA, United States, (3)UNAM, ICMyL, Mexico City, Mexico, (4)Universidad Nacional Autonoma de Mexico, Posgrado en Ciencias Biológicas, Mexico City, Mexico, (5)Universidad Nacional Autonoma de Mexico, Instituto de Geología, Mexico City, Mexico, (6)IPN, Escuela Nacional de Ciencias Biológicas, Mexico City, Mexico, (7)UNAM National Autonomous University of Mexico, Instituto de Geología, Mexico City, Mexico
Microbialites are the modern analogues of ancient microbial consortia. Their existence extends from the Archaean (~3500 mya) until present and their lithified structure evidences the capacity of microbial communities to mediate mineral precipitation. Living microbialites are a useful study model to test the mechanisms involved in carbonates and other minerals precipitation. Here, we studied the chemical composition, the biomass and the microbial structure of extant microbialites. All of these were found in Mexico, in water systems of different and characteristic ionic firms. An elemental analysis (C:N) of microbial biomass was performed and total P was determined. To explore the chemical composition of microbialites as a whole, X-ray diffraction analyses were performed over dry microbialites. While overall inorganic carbon content (carbonates) represented >70% of the living layer, a protocol of inorganic carbon elimination was performed for each sample resulting in organic matter contents between 8 and 16% among microbialites. Stoichiometric ratios of C:N:P in microbialite biomass were different among samples, and the possibility of P limitation was suggested mainly for karstic microbialites, N limitation was suggested for all samples and, more intensively, for soda system microbialites. A differential capacity for biomass allocation among microbialites was observed. Microbialites showed, along the biogeographic gradient, a diverse arrangement of microbial assemblages within the mineral matrix. While environmental factors such as pH and nitrate concentration were the factors that defined the general structure and diversity of these assemblages, we intend to test if the abundance of major ions and trace metals are also defining microbialite characteristics (such as microbial structure and biomass).

This work contributes to define a baseline of the chemical nature of extant microbial consortia actively participating in mineral precipitation processes.