WAX ESTERS SYNTHESIZED BY ACIDOPHILIC EUKARYOTE EUGLENA MUTABILIS, A BIOCHEMICAL RELICS OF THE ANAEROBIC PAST OF THE EARTH?

Acid mine drainage (AMD) systems offer excellent natural laboratories to study relatively unique aspects of geobiology and biogeochemistry of modern microbial mats. The most conspicuous feature of some of these AMD systems is the presence of Fe-rich stromatolites overlain by dense biofilms of photosynthetic eukaryotes. Recent research on the geobiology and biogeochemistry of AMD systems has provided new insights into the role of eukaryotes in the formation of stromatolites and oxygenation of the atmosphere on early Earth. The living biofilms and biogeochemical processes that produce these Fe-rich stromatolites in AMD environments may serve as potential analogs for those eukaryotes that may have contributed to the formation of Late Archean–Early Proterozoic banded iron formation. We collected biofilm samples of acidophilic protist Euglena mutabilis from the Green Valley coal-mining site in western Indiana in September 2006. Lipid analysis showed that E. mutabilis contained abundant wax esters of (by total carbon number) C_25-C32. The major fatty acids of the wax esters were C_12-14 short-chain fatty acids. These wax esters are different from those commonly found in marine animals and terrestrial plants which have carbon numbers of C_28-46. We speculate that the wax esters may be the biochemical relics of the anaerobic past of the Earth and the detection of these compounds has important implications for the evolution of eukaryotes and the paleoenvironmental conditions on early Earth. This type of biochemical machine may have allowed early eukaryotes to survive recurrent anoxic conditions on early Earth.