LONG-TERM SURVIVAL OF MICROORGANISMS PRESERVED IN HALITES, SALAR DE UYUNI SALT CORE, BOLIVIA

A 220 m long salt core, >276 ka, from the Salar de Uyuni is being analyzed for preservation of trapped microorganisms in halite brine inclusions on time scales of 10³ to 10⁵ years. This research is testing whether the preservation of viable microorganisms in fluid inclusions depends on 1) the age of the halite, or 2) the environment of crystal growth and organism entrapment, or both.

The Uyuni salt core was dated by ¹⁴C and U-series methods to depths of 110 m. The core is composed of mud, bedded halite, and massive mud/halite/gypsum, deposited in perennial lakes (fresh water to halite saturation) and saline pans and mudflats. Primary textures in bedded halite indicate that crystals and enclosed fluid inclusions all formed from surface brines and are therefore the same age as the dated interval, which ensures that recovered microbes are authentically ancient.

Halite samples collected from the core were cleaved into single crystals; stringent analysis prevented contamination by modern organisms. The methods include: sterilization of all equipment and work surfaces, surface sterilization of individual crystals in concentrated NaOH under a laminar flow hood, use of controls, and replication of experiments within the laboratory and independently in a separate laboratory. Individual halite crystals were dissolved in nutrient broths to release fluid inclusion contents and allow any microorganisms contained therein to be cultured. The DNA from cultured microbes is amplified via PCR and then sequenced. This information on microbial persistence can be applied to microbial preservation in other ancient evaporites from various locations, including Mars.