Lipid biomarkers and carbon-isotopes of modern travertine deposits (Yellowstone National Park, USA): Implications for biogeochemical dynamics in hot-spring systems
CHUANLUN L. ZHANG,1 BRUCE W. FOUKE,2 GEORGE T. BONHEYO,2
AARON D. PEACOCK,3 DAVID C. WHITE,3 YONGSONG HUANG,4
and CHRISTOPHER S, ROMANEK1
1Savannah River Ecology Laboratory, University of Georgia,
Drawer E, Aiken, SC 29802, USA
2Departrnent 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
4Departrnent of Geological Sciences, Brown University, Providence,
RI 02912, USA
Abstract-Lipid biomarkers and 13C fractionation
patterns were used to understand the dynanmics 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 bacterial16S rRNA gene sequences in the Spring AT-1
travertine facies (Fouke et al., 2003).
The S13C composition of total biomass within the microbial
mats decreases from -16.1%0 in the vent to -23.5%0 in the distal slope.
However, lower values occur in the pond (-26.0%0) and the proximal slope(-28.0%0)
between the vent and the distal slope. Isotopic compositions of PLFA and
GLFA have variations similar to those of total biomass. The average SI3C
values of PLFA are -12.4 :t 5.2%0 (n = 10 individual fatty acids, same
below) in the vent, -33.0 :t 3.1%0 (n = 11) in the pond, -33.7 :t 3.8%0
(n = 16) in the proximal slope, and -22.4:t 3.4%0 (n = 10) in the distal
slope; the average SI3C values ofGLFA are -19.6 :t 3.0%0 (n = 3) in the
vent, -30.4 :t 4.7%0 (n = 8) in the pond, -36.9 :t 2.8%0 (n = 12) in the
proximal slope, and -27.9 :t 3.1%0 (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 modem hot-spring systems. Copyright
@ 2004 Elsevier Ltd
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.
