To all MEB, GeoBio and Earth Sci
When: 1100 am Monday 2 June 2014
Where: Torrey Webb Room/ AHF
Microbialite genetic diversity and N cycling
Luisa I Falcón
Bacterial Ecology Lab., Institute of Ecology, UNAM
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.