To all MEB, GeoBio and Earth Sci

When: 1100 am Monday 2 June 2014

Where: Torrey Webb Room/ AHF

SPECIAL SEMINAR

Microbialite genetic diversity and N cycling

Luisa I Falcón

Bacterial Ecology Lab., Institute of Ecology, UNAM

falcon@ecologia.unam.mx

Microbialites have played an important role in the early history of life on Earth with fossilized forms representing the oldest evidence of life on our planet dating back to 3500 Ma. Extant microbialites have been suggested to be highly productive and diverse communities with an evident role in the cycling of major elements, and in contributing to carbonate precipitation. We have analyzed microbial genetic diversity of microbialites living in different types of environments throughout Mexico, including desert ponds, coastal lagoons and crater-lakes. Microbialite communities are very diverse (H′ = 6–7) and show geographic variation in composition, as well as an environmental effect related to pH and conductivity, which together explain 33% of the genetic variation. N cycle pathways including N₂ fixation, nitrification, denitrification and anammox are evident in the potential community, but only N₂ fixation by heterocyst-forming Cyanobacteria within Nostocales are actively transcribed. Our studies suggest that N limitation in the environment strongly favors autotrophy and diazotrophy and restricts remineralization pathways via denitrification and anammox. Cyanobacteria that form heterocysts and are actively transcribing for N₂ fixation, are fundamental players in microbialites since they are responsible for providing reduced N –amides, C in lipids and carbohydrates, and host in their external cell membranes the main sites of carbonate mineral precipitation.