NASA Astrobiology Institute (NAI)

Field work at Cuatro Ciénegas, Mexico has focused on understanding unique
structures called microbialites. These are colonies of bacteria that have
been encased by minerals that have precipated out of the water surrounding
them. This process have been going on for 2 and a half billion years on
earth. The work we are doing is using experiments to see how the environment
can affect the genes in these bacteria to create the microbialites. We do
this to improve our understanding of how they utilize two very important atoms, carbon and nitrogen. By studying these Earth bacteria we can better understand how microbialites interact with their environemnt, and whether or not microbialites might exist and be detectable in extrasolar environments.

The team has provided a functional estimation of the bacterial (Breitbart et, in press, Environmental Microbiology) and viral metagenomes (Desnues et al, Nature, 2007) of two different stromatolite morphologies from Cuatro Ciénegas. The bacterial metagenome was combined with isotopic analysis, resulting in a functional estimation of the metabolic potential of the bacterial component of the stromatolites. The viral metagenome (which coincidently is freshwater in habitat) was compared to marine viral metagenomes and found to harbor a marine ancestry explainable by the known geological history of the Cuatro Ciénegas valley. A model of possible genome architecture agents of change and their requirement for phosphorus (Souza et al, Nature Micorbiology Reviews, 2008), revealed that phosphorus limitation likely enhances speciation and the whole genome sequence of a Bacillus isolate from Cuatro Ciénegas (Alcaraz et al, PNAS, 2008) showed direct evidence for geographic adaptation via horizontal gene transfer with non-related bacterial constituencies.