Biomarker studies on microbial carbonates: Extractable lipids of a Calcifying Cyanobacterial mat (Everglades, USA)

Summary Biomarker investigations are applied to the free lipid fractions of a naturally grown freshwater microbial mat, constructed by calcifying cyanobacteria (Scytonema sp. andSchizothrix sp.). The absolute and relative concentrations of hydrocarbons, free alcohols and carboxylic acids are studied and their probable biological precursors are discussed. A significant signal of cyanobacterial lipids is recognized by the strong predominance ofn-heptadecane (C₁₇),n-heptadecene, two monomethyl-heptadecanes, and the pentacyclic triterpenoid diploptene. Their occurrences parallel the lipid distributions found in pure cultured cyanobacteria and in recent cyanobacterial mats grown in particular environments (hypersaline, lagoonal, hot spring). The observed compound signature appears to be a suitable reference for environments, where cyanobacteria are directly associated with theloci of carbonate precipitation and thus, rock formation. In the studied material, a significant contribution of organic matter from other sources, especially higher plants is characterized by the occurrence of several specific marker compounds, namely lup-20(29)-ene-3-ol, high molecular weightn-alkanes and carboxylic acids. Although these components comprise a notably high portion of the sample’s lipid inventory, they are shown to be distinguished easily from the signal left by the predominant mat building organisms.