Microbialite genetic diversity and composition relate to environmental variables

Microbialites have played an important role in the early history of life on Earth. Their fossilized forms represent 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. Although their ecological and evolutionary importance has been recognized, the study of their genetic diversity is yet scanty. The main goal of this study was to analyse microbial genetic diversity of microbialites living in different types of environments throughout Mexico, including desert ponds, coastal lagoons and a crater-lake. We followed a pyrosequencing approach of hypervariable regions of the 16S rRNA gene. Results showed that microbialite communities were very diverse (H' = 67) and showed geographic variation in composition, as well as an environmental effect related to pH and conductivity, which together explained 33% of the genetic variation. All microbialites had similar proportions of major bacterial and archaeal phyla.