PRESERVATION OF HALOPHILIC MICROORGANISMS IN HALITE FLUID INCLUSIONS, SALINE VALLEY, CALIFORNIA

A natural red halophile bloom in the Saline Valley, California, brine pool, March 2004, showed the mechanisms by which microorganisms are trapped inside halite crystals. Increased inflow in the preceding months increased the depth (< 1m) and lowered the salinity of the surface brines. In late March, halophilic Archaea, Bacteria and algae (Dunaliella) thrived in bright red brines at salinities of 25-30% and temperatures of 34-36° C. By early April, salinities rose above 30%, the bloom declined, and the water column cleared.

Halite crystals growing in the Saline Valley brine pool form as crystal rafts at the air/brine interface, and as chevrons and clear vertical crystals at the brine bottom. Growing crystals trap microorganisms in fluid inclusions, directly from the water column (organisms in suspension or as they settle out), or attached to mud particles that settle onto crystals. Halophilic microbes are best captured in fluid inclusions during the early stages of halite precipitation because the microbial community is still active.

High magnification light microscopy (~1500x) of fluid inclusions in halites collected in 1994 and 2004 revealed motile microorganisms. Polymerase chain reaction (PCR) amplification of DNA fragments was done on the same 1994 and 2004 halites following surface sterilization and dissolution. Positive PCR results were obtained using primers for Bacteria and Archaea, which indicates microorganisms were trapped in the halite crystals. Red halophilic microorganisms were also cultured for isolation and characterization from the same halites.

Salt cores from Saline Valley drilled to depths of 100 m preserve a 150,000-year record of saline paleoenvironments. Halite crystals and fluid inclusions from these salt cores may contain trapped microorganisms and their DNA. Systematic analysis of samples from the salt cores (imaging microparticles for motility, PCR amplification of trapped DNA, and culturing of microorganisms) will test the limits of microbial survivability on this planet and possibly others.