MICROBIAL BIOMASS AND COMMUNITY STRUCTURE OF A STROMATOLITE FROM AN ACID MINE DRAINAGE SYSTEM AS DETERMINED BY LIPID ANALYSIS

Lipids were extracted from a Fe-rich stromatolite from acid mine drainage (AMD) at the Green Valley coal-mine site (GVS) in western Indiana to determine the microbial biomass and community structure. The distribution of biomarkers corresponded well to the layers in the laminated stromatolite. The top layer of the stromatolite is dominated by phototrophic microeukaryotes, which constitute 83% of the total biomass. Prokaryotic microorganisms dominate the lower layers. The presence of terminal methyl-branched fatty acids suggests the presence of Gram-positive bacteria, and the mid methyl-branched fatty acids indicate the presence of sulfate-reducing bacteria. Fungi appear to also be an important part of the AMD microbial communities, as suggested by sterol profiles and the presence of polyunsaturated fatty acids. Hydroxy fatty acids and C19 cyclopropane fatty acids were also detected and likely originated from acid-producing acidophilic bacteria. The presence of Archaea is indicated by abundant phospholipid ether-linked isoprenoid hydrocarbons and fatty acids, typical lipids of Archaea. The AMD Fe-rich stromatolites at GVS, thus, appear to be formed by interactions of microbial communities composed of all three domains of life—Archaea, Bacteria, and Eukarya. Identification of microeukaryote-dominated stromatolites implicates their prominent role in the formation and preservation of these Fe-rich structures. In addition, the production of oxygen through photosynthesis by these organisms in AMD systems may be important for retrodicting the interaction of microbial communities in Precambrian environments in the production of microbially mediated sedimentary structures and oxygenation of the early atmosphere.