Lipid Biomarkers and Carbon Isotope Signatures of a Microbial (Beggiatoa) Mat Associated with Gas Hydrates in the Gulf of Mexico
Chuanlun L. Zhang,1 Zhiyong Huang,1 James Cantu,2
Richard D. Pancost,3 Robin L. Brigmon,4 Timothy
W. Lyons,5 and Roger Sassen6
Department of Marine Sciences and Savannah River Ecology Laboratory,
University of Georgia, 1 and Savannah River Technology Center,
4 Aiken, South Carolina; Center for Biomarker Analysis, The
University of Tennessee, Knoxville, Tennessee2; Organic Geochemistry
Unit, Bristol Biogeochemistry Research Centre, School of Chemistry, University
of Bristol, Bristol, United Kingdom3; Department of Geological
Sciences, University of Missouri, Columbia, Missouri5; and
Geochemical and Environmental Research Group, Texas A&M University,
College Station, Texas6
Received 10 May 2004/Accepted 29 October 2004
White and orange mats are ubiquitous on surface sediments associated with
gas hydrates and cold seeps in the Gulf of Mexico. The goal of this study
was to determine the predominant pathways for carbon cycling within an
orange mat in Green Canyon (GC) block GC 234 in the Gulf of Mexico. Our
approach incorporated laser-scanning confocal microscopy, lipid biomarkers,
stable carbon isotopes, and 168 rRNA gene sequencing. Confocal microscopy
showed the predominance of filamentous microorganisms (4 to 5 ~m in diameter)
in the mat sample, which are characteristic of Beggiatoa. The phospholipid
fatty acids extracted from the mat sample were dominated by 16:1w7cft
(67%), 18:1w7c (17%), and 16:0 (8%), which are consistent with lipid profiles
of known sulfur-oxidizing bacteria, including Beggiatoa. These
results are supported by the 168 rRNA gene analysis of the mat material,
which yielded sequences that are all related to the vacuolated sulfur-oxidizing
bacteria, including Beggiatoa, Thioploca, and Thiomargarita.
The 813C value of total biomass was -28.6%; those of individual
fatty acids were -29.4 to -33.7%. These values suggested heterotrophic
growth of Beggiatoa on organic substrates that may have 813C values characteristic
of crude oil or on their by.products from microbial degradation. This
study demonstrated that integrating lipid biomarkers, stable isotopes,
and molecular DNA could enhance our understanding of the metabolic functions
of Beggiatoa mats in sulfide-rich marine sediments associated
with gas hydrates in the Gulf of Mexico and other locations.
SREL Reprint #2825
Zhang, C. L., Z. Huang, J. Cantu, R. D. Pancost, R. L. Brigmon, T. W. Lyons and R. Sassen. 2005. Lipid biomarkers and carbon isotope signatures of a microbial (Beggiatoa) mat associated with gas hydrates in the Gulf of Mexico. Applied and Environmental Microbiology 71:2106-2112.
