SREL Reprint #2779




Lipid biomarkers and carbon-isotopes of modern travertine deposits (Yellowstone National Park, USA): Implications for biogeochemical dynamics in hot-spring systems

Chuanlun L. Zhang1, Bruce W. Fouke2, George T. Bonheyo2, Aaron D. Peacock3, David C. White3, Yongsong Huang4, and Christopher S. Romanek1

1Savannah River Ecology Laboratory, University of Georgia, Drawer E, Aiken, SC 29802, USA
2Department of Geology, University of lllinois, 245 Natural History Building, Urbana, IL 61801, USA
3Center for Biomarker Analysis, The University of Tennessee, Knoxville, TN 37932, USA
4Department of Geological Sciences, Brown University, Providence, RI 02912, USA

Abstract: Lipid biomarkers and 13C fractionation patterns were used to understand the dynamics of carbon cycling during microbial metabolisms in different environments of travertine precipitation (called facies) at Spring AT-1 on Angel Terrace in the Mammoth Hot Springs complex of Yellowstone National Park, USA. Microbial mats that encrust travertine deposits were collected for analyses of lipid biomarkers and carbon isotopes along the continuous drainage outflow system of Spring AT-1. The spring water exhibits a continuous temperature drop from 71°C in the vent at top to 24°C in the distal slope at bottom. Phospholipid fatty acids (PLFA) and glycolipid fatty acids (GLFA) exhibit distinctly different compositions in each of the facies, which are consistent with partitioning of the bacterial 16S rRNA gene sequences in the Spring AT-1 travertine facies (Fouke et al., 2003).
The δ13C composition of total biomass within the microbial mats decreases from -16.1‰ in the vent to -23.5‰ in the distal slope. However, lower values occur in the pond (-26.0‰) and the proximal slope
(-28.0‰) between the vent and the distal slope. Isotopic compositions of PLFA and GLFA have variations similar to those of total biomass. The average δ13C values of PLFA are -12.4 ± 5.2‰ (n = 10 individual fatty acids, same below) in the vent, -33.0 ± 3.1‰ (n = 11) in the pond, -33.7 ± 3.8‰ (n = 16) in the proximal slope, and -22.4 ± 3.4‰ (n = 10) in the distal slope; the average δ13C values of GLFA are -19.6 ± 3.0‰ (n = 3) in the vent, -30.4 ± 4.7‰ (n = 8) in the pond, -36.9 ± 2.8‰ (n = 12) in the proximal slope, and -27.9 ± 3.1‰ (n = 13) in the distal slope. In particular, fatty acids in the vent are enriched in 13C relative to the total biomass, which is consistent with the notion that the biosynthetic pathways of the extant microbial community in the vent may be dominated by Aquificales using the reversed tricarboxylic acid cycle. Fractionations between fatty acids and total biomass in the pond, the proximal slope and the distal slope suggest the involvement of other biosynthetic pathways for CO2 fixation by extant microbial populations. The results indicate that lipid biomarkers provide valuable information on the changing diversity and activity of microbial communities in different depositional environments. Carbon-isotope fractionations, on the other hand, can provide insight into the operating biosynthetic pathways associated with different organisms in the changing environment. This integrated approach may serve as a powerful tool for identifying functional metabolism within a community and identify shifts in microbial community structure in modern hot-spring systems.

Keywords: Phospholipid fatty acids, glycolipid fatty acids, lipid biomarkers, stable carbon isotopes, Aquificales, cyanobacteria, green sulfur bacteria, green non-sulfur bacteria, Angel Terrace, Mammoth Hot Springs, Yellowstone National Park

SREL Reprint #2779

Zhang, C. L., B. W. Fouke, G. T. Bonheyo, A. D. Peacock, D. C. White, Y. Huang, and C. S. Romanek. 2004. Lipid biomarkers and carbon-isotopes of modern travertine deposits (Yellowstone National Park, USA): implications for biogeochemical dynamics in hot-spring systems. Geochimica et Cosmochimica Acta 68:3157-3169.

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