LONG-TERM SURVIVAL OF MICROORGANISMS AND DNA PRESERVED IN HALITES, DEATH VALLEY SALT CORE, CALIFORNIA

A 186-m-long (200 kyr) salt core from Death Valley, California contains fluid inclusions in halites that preserve microorganisms and DNA for up to 10⁵ years. Two independent laboratories cultured halophilic Archaea from fluid inclusions in halite. Three paleolake intervals (core depths of 12.9 m = ~22 ka; 17.9 m = ~34 ka; 84.9 m = ~97 ka) preserved these halophiles in fluid inclusions in halites that crystallized on the lake bottom. Polymerase chain reaction (PCR) amplified ancient bacterial DNA from fluid inclusions in halites from depths of 7.5 m (9.6ka) and 84.9 m in the salt core. These results collectively indicate that fluid inclusions in halites crystallizing on the brine bottom of Death Valley paleolakes trapped and preserved halophilic bacteria, Archaea, and ancient DNA. The following criteria are used to verify that amplified DNA and cultured halophilic bacteria and Archaea are truly ancient: 1) halite samples are well-dated by U-series methods, 2) work is done under a laminar flow hood, 3) surfaces, reagents, and tools are sterilized before use, 4) individual halite crystal samples are surface sterilized, 5) controls (positive and negative) are used, and, 6) results are replicated intra-laboratory and in an independent laboratory. Continued work on ancient halites in the Death Valley core from different paleoenvironments (e.g., perennial saline lake, shallow ephemeral lake, or salt pan) will address which environments preserve the highest numbers and most diverse populations of microorganisms. That paleoenvironmental information will help clarify where to search for microbial life in fluid inclusions in ancient evaporites on Earth and possibly Mars.