MOLECULAR CHARACTERISTICS OF DESICCATED MICROBIAL MATS: 2. ENVIRONMENTAL CONSTRAINTS ON LIPID COMPOSITIONS

Lakes in Warner Valley, Oregon, experience significant changes in water balance caused by seasonal to decadal scale droughts. They are fed by springs of varied temperature (9 - 71°C) and pH (6.5 - 8.3), typically originating from fractures within Oligocene basalt, that are HCO3- dominated, and support microbial mats. From late spring through summer the lake waters are concentrated by evaporation, which produces wide variations in their chemistry and thermal structure from the interplay of supply/evaporation. Water chemistries range from moderately to highly alkaline to sulfate-chloride dominated, varying widely in pH (8.3-10.5) and total dissolved solids (25-300,000 ppm). Throughout the system, microbial mats in the lakes, playas, and springs are controlled by temperature (psychrophiles, mesophiles, thermophiles, and hyperthermophiles) and chemistry (alkalophiles and halophiles), augmented by seasonally dynamic microbial populations that respond to profound shifts in temperature, pH and ion and metal concentrations.

The microbial mats of specific lakes contain wax esters and branched alkanes as the major lipid constituents of their unsaponified extracts. The compositions and distributions of both series of lipids are unprecedented, and vary among the environments. Wax esters are low in abundance among the lipids from live mats in alkaline waters (average alkalinity = 122 mg/l as total CaCO3, pH = 9.1 - 10.5, TDS = 237 ppm; temperature = 19.6°C), whereas they dominate the ‘aromatic' fraction (toluene eluate) of analogous desiccated mats. The wax esters range from C26 to C50 and are comprised of a simpler range of carboxylic acid moieties than those found in marine and hot spring environments, except that they include isoprenoid components only previously observed among the lipids of marine bacteria fed on phytol.