Long term preservation of DNA in halite deposits: Insights into ancient archaeal and algal communities

Primary fluid inclusions in evaporite minerals such as Halite, Gypsum, etc., contain accurate records of the environments in which they originally formed, and have been used extensively in reconstruction of the Earth's geoclimatic history. Additionally, these inclusions contain evidence of the microbial ecosystem that once existed in these environments, in the form of preserved cells/cell structures, and biomolecules such as DNA, Carotenoids, etc. Investigations on biomaterials trapped in these fluid inclusions imply long-term survival of prokaryotes, and preservation of DNA, for periods up to hundreds of millions of years ago. However, possibility for contamination from modern environmental and laboratory sources makes these results controversial. To address these issues, we developed robust surface sterilization and DNA extraction protocols, enabling the efficient retrieval of the small amounts of DNA trapped within these ancient samples, while completely removing any contaminating DNA. Using these protocols, we were able to a) successfully demonstrate the authenticity of two previously cultured ancient archaea, b) characterize haloarchaeal diversity in halite up to 34,000 years old, and c) characterize green algal diversity in halite up to 150,000 years old.