Microbialites from distant environments in Mexico. uncultured organism

Microbialites have played an important role in the early history of life on Earth. Dating back to 3500 Ma, their fossilized forms represent the oldest evidence of life on our planet. Extant microbialites have been suggested to be highly productive. Although their ecological and evolutionary importance has been recognized, the study of the genetic diversity of the associated microbial communities is only beginning. Here we attempt to estimate the prokaryotic genetic diversity of actively growing layers of microbialites living in different types of environment. We used pyrosequencing of the hypervariable regions of the 16S rDNA gene to analyze genetic diversity and test if the genetic community structure is related to environmental variables. This study includes microbialites from 10 localities from sites in the Cuatro Cienegas basin which is a desert oasis in northern Mexico, the Alchichica crater-lake in central Mexico, and two coastal lagoons in the Yucatan Peninsula. Microbialite communities showed geographic variation and high diversity related to the environmental conditions. The 3 most important environmental variables (pH, conductivity, NO3) explained a significant portion of the among-site genetic variation, having together an adjusted R2 of 0.383 and a permutational p-value of 0.001. This study also shows a remarkable aspect of the community composition where all microbialites shared major phyla and their proportions were highly similar among sites: Proteobacteria were the most abundant (36-45 %), followed by Planctomycetes (15-31%), Verrucomicrobia (3-11%), Cyanobacteria (1-16%) and Bacteroidetes (5-9%). Altogether, this is the first study that reports on how the structure of microbialite communities is deeply structured by environmental variables, which in turn are being influenced by global warming.