HR: 1330h
AN: B12A-0759    [PDF]
TI: Lipid Biomarkers and Molecular Carbon Isotopes for Elucidating Carbon Cycling Pathways in Hydrothermal Vents
AU: * Zhang, C L
EM: zhang@srel.edu
AF: University of Georgia, Department of Marine Sciences, Athens, GA 30602 United States
AU: Dai, J
EM: reginadai2000@yahoo.com
AF: University of Georgia, Department of Marine Sciences, Athens, GA 30602 United States
AU: Campbell, B
EM: bjc@udel.edu
AF: University of Delaware, Center for Marine Genomics, College of Marine Studies, Lewes, DE 19958 United States
AU: Cary, C
EM: caryc@udel.edu
AF: University of Delaware, Center for Marine Genomics, College of Marine Studies, Lewes, DE 19958 United States
AU: Sun, M
EM: mysun@arches.uga.edu
AF: University of Georgia, Department of Marine Sciences, Athens, GA 30602 United States
AB: Increasing molecular evidence suggests that hydrothermal vents in mid-ocean ridges harbor large populations of free-living bacteria, particularly the epsilon Proteobacteria. However, pathways for carbon metabolism by these bacteria are poorly known. We are addressing this question by analyzing the lipid biomarkers and their isotope signatures in environments where the epsilon Proteobacteria are likely predominant. Solid materials were collected from hydrothermal vents in the East Pacific Rise and at the Guaymas Basin in the Gulf of California. Fatty acids extracted from these samples are dominated by 16:0 (27-41%), 18:0 (16-48%), 18:1 (11-42%), 16:1 (7-12%), and 14:0 (5-28%). In addition, 15:0 and anteiso-15:0 are significantly present (2-3%) in samples from the Guaymas Basin. The isotopic compositions of these fatty acids range from -15.0\permil to -33.1\permil with the most positive values occurring only in monounsaturated fatty acids (16:1 and 18:1). We are currently unable to assign these biomarkers to any of the epsilon Proteobacteria because biomarkers are poorly known for these organisms isolated from the vents. However, no polyunsaturated fatty acids were detected in these samples, which are consistent with the absence of vent animals at the sampling sites. Signature biomarkers of 20:1 and cy21:0, which are characteristic of the thermophilic chemolithoautotrophs such as {\it Aquificales}, are also absent in these samples. These results imply that the deeply branched {\it Aquificales} species do not constitute the major microbial community in these vent environments. The large range of molecular isotopic compositions suggests that these lipids are synthesized from various carbon sources with different isotopic compositions or through different biosynthetic pathways, or both. We are currently measuring the isotopic compositions of the total organic carbon in the bulk samples and will determine the fractionations between lipid biomarkers and the total organic carbon. Molecular DNA data from these vent environments indicate that the reversed TCA cycle may be used for CO$_{2}$ fixation by the epsilon Proteobacteria for chemolithoautotrophic growth. Isotopic fractionation patterns between lipid biomarkers and the bulk organic carbon can provide independent information on this unique biosynthetic pathway.
DE: 0400 Biogeosciences
DE: 0614 Biological effects
DE: 1045 Low-temperature geochemistry
DE: 4803 Bacteria
DE: 4805 Biogeochemical cycles (1615)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting