MOLECULAR CHARACTERISTICS OF DESICCATED MICROBIAL MATS: 1. EVOLUTION OF WAX ESTERS AS STORAGE LIPIDS

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.

Wax ester production and abundance is enhanced in microbial mats undergoing desiccation compared to hydrated mats. The wax esters in desiccated mats 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. Typically recovery of lipids from microbial mats typically includes a saponification step, which is critical for characterization of phospholipid fatty acids and their distribution, but precludes recovery of information regarding the occurrence and composition of wax esters. The longer chain length of these wax esters is consistent with lower solubilities and greater resistance to degradation and oxidation with desiccation. Seasonal rehydration of this environment can then be considered a natural saponification step where initial hydration allows for regeneration of acids and alcohols. Breakdown of the wax ester thereby provides storage lipids and the resulting high molecular weight materials for cell walls for the next viable microbial generation, and represents a significant evolutionary pathway in lipid biosynthesis and usage.