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Appl. Environ. Microbiol., Feb 1995, 576-582, Vol 61, No. 2
LL Jahnke, RE Summons, LM Dowling and KD Zahiralis
A lipid analysis of the tissues of a cold-seep mytilid mussel collected
from the Louisiana slope of the Gulf of Mexico was used in conjunction with
a compound-specific isotope analysis to demonstrate the presence of
methanotrophic symbionts in the mussel gill tissue and to demonstrate the
host's dependence on bacterially synthesized metabolic intermediates. The
gill tissue contained large amounts of group-specific methanotrophic
biomarkers, bacteriohopanoids, 4-methylsterols,
lipopolysaccharide-associated hydroxy fatty acids, and type I-specific 16:1
fatty acid isomers with bond positions at (Delta)8, (Delta)10, and
(Delta)11. Only small amounts of these compounds were detected in the
mantle or other tissues of the host animal. A variety of cholesterol and
4-methylsterol isomers were identified as both free and steryl esters, and
the sterol double bond positions suggested that the major bacterially
derived gill sterol [11.0%
4(alpha)-methyl-cholesta-8(14),24-dien-3(beta)-ol] was converted to host
cholesterol (64.2% of the gill sterol was cholest-5-en-3(beta)-ol). The
stable carbon isotope values for gill and mantle preparations were,
respectively, -59.0 and -60.4(permil) for total tissue, -60.6 and
-62.4(permil) for total lipids, -60.2 and -63.9(permil) for phospholipid
fatty acids, and -71.8 and -73.8(permil) for sterols. These stable carbon
isotope values revealed that the relative fractionation pattern was similar
to the patterns obtained in pure culture experiments with methanotrophic
bacteria (R. E. Summons, L. L. Jahnke, and Z. Roksandic, Geochim.
Cosmochim. Acta 58:2853-2863, 1994) further supporting the conversion of
the bacterial methylsterol pool.
Copyright © 1995, American Society for Microbiology
Identification of Methanotrophic Lipid Biomarkers in Cold-Seep Mussel Gills: Chemical and Isotopic Analysis
National Aeronautics and Space Administration, Ames Research Center, Moffett Field, California 94035-1000; Australian Geological Survey Organisation, Canberra, ACT 2601, Australia; and SETI Institute, Mountain View, California 94043
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