oa Compound-Specific Carbon Isotope Fractionation Patterns of Diverse Cyanobacterial Lipids

Cyanobacteria are major primary producers in a variety of aquatic environments as well as in hydrothermal ecosystems and desert soil crusts. Their lipids comprise a significant fraction of most fossil hydrocarbon assemblages. However, few studies have examined the isotopic fractionation patterns of lipid biosynthesis in cyanobacterial cultures. In 1973, Calder and Parker reported the isotopic fractionation results for bulk lipid fractions from four cultured ‘blue-green algae.’ In 1997, Sakata and colleagues reported the carbon isotopic compositions of bulk biomass, total lipid extract, and individual lipids from cultures of a single taxon, Synechocystis UTEX 2470.

To characterize the stable carbon isotope ratios of cyanobacterial lipids, eight cultures of comprised of Synechococcus, Synechocystis, Nostoc, and Fischerella species were grown using isotopically characterized CO2 gas. The bulk biomass, total lipid extract, and individual lipids from these cultures were analyzed, revealing offsets from the carbon source and biomass that appear to reflect differences in growth characteristics. The resulting index of the carbon isotope compositions of individual lipids in assorted cyanobacteria may aid both in the determination of the relative inputs of cyanobacteria to sedimentary organic matter and in the development of pCO2 proxies based on the stable isotopic compositions of phytoplankton-derived lipid biomarkers.