LIPID BIOMARKERS AND STABLE CARBON ISOTOPE SIGNATURES OF MICROBIAL SYSTEMS

Carbon cycling in low-temperature sedimentary environments is mediated by diverse groups of microorganisms. Different organisms have characteristic lipid biomarkers and carbon-isotope signatures, which are powerful tools for understanding the pathways of carbon cycling by microbial processes in natural environments. Precise information on isotopic fractionations by microorganisms can only be obtained using pure cultures under known conditions. We have taken an experimental approach to study isotopic fractionations associated with lipid biosynthesis of several groups of microorganisms. Results indicate that characteristic fractionations can be attributed to biosynthetic pathways in the context of heterotrophic versus autotrophic growth and types of electron donors and acceptors used. These results may have direct relevance to natural systems. For example, the laboratory-observed fractionations between lipids and biomass for a thermophilic chemolithoautotrophic bacterium, Persaphanella marina, are similar to the fractionations observed for a hot-spring microbial mat, which is dominated by the same type of bacteria Aquificales (Fouke et al., 2003; Zhang et al., in review). Thus isotopic fractionations of known microorganisms can provide valuable information for natural observations of isotope bio-signatures, particularly in the context of geochemical conditions conducive to microbial growth in the sedimentary environments.

References Cited: Fouke B. W., Bonheyo G. T., Sanzenbacher B., and Frias-Lopez J. (2003) Can. J. Earth. Sci. in press. Zhang C. L., Fouke B. W., Bonheyo G., Peacock A., White D. C., Huang Y., and Romanek C. S. Geochim. Cosmochim. Acta (in review).