BIOMARKER STUDIES ON MICROBIAL CARBONATES - EXTRACTABLE LIPIDS OF A CALCIFYING CYANOBACTERIAL MAT (EVERGLADES, USA)

Biomarker investigations ate applied to the free lipid fractions of a naturally grown freshwater microbial mat, constructed by calcifying cy anobacteria (Scytonema sp. and Schizothrix sp.). The absolute and rela tive concentrations of hydrocarbons, free alcohols and carboxylic acid s are studied and their probable biological precursors are discussed. A significant signal of cyanobacterial lipids is recognized by the str ong predominance of n-heptadecane (C-17) n-heptadecene, two monomethyl -heptadecanes, and the pentacyclic triterpenoid diploptene. Their occu rrences parallel the lipid distributions found in pure cultured cyanob acteria and in recent cyanobacterial mats grown in particular environm ents (hypersaline, lagoonal, hot spring). The observed compound signat ure appears to be a suitable reference for environments, where cyanoba cteria are directly associated with the loci of carbonate precipitatio n and thus, rock formation. In the studied material, a significant con tribution of organic matter from other sources, especially higher plan ts is characterized by the occurrence of several specific marker compo unds, namely lup-20(29)-ene-3-ol, high molecular weight n-alkanes and carboxylic acids. Although these components comprise a notably high po rtion of the sample's lipid inventory, they are shown to be distinguis hed easily from the signal left by the predominant mat building organi sms.