Jahnke L L, Summons R E, Dowling L M, Zahiralis K D
National Aeronautics and Space Administration, Ames Research Center, Moffett Field, California 94035-1000, USA.
Appl Environ Microbiol. 1995 Feb;61(2):576-82. doi: 10.1128/aem.61.2.576-582.1995.
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% for total tissue, -60.6 and -62.4% for total lipids, -60.2 and-63.9% for phospholipid fatty acids, and -71.8 and 73.8% 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 bacteria methylsterol pool.
对从墨西哥湾路易斯安那斜坡采集的冷泉贻贝组织进行脂质分析，并结合化合物特异性同位素分析，以证明贻贝鳃组织中存在甲烷营养共生体，并证明宿主对细菌合成的代谢中间体的依赖性。鳃组织含有大量特定类群的甲烷营养生物标志物、细菌藿烷类、4-甲基甾醇、脂多糖相关羟基脂肪酸以及在δ8、δ10和δ11处具有双键位置的I型特异性16:1脂肪酸异构体。在宿主动物的外套膜或其他组织中仅检测到少量这些化合物。多种胆固醇和4-甲基甾醇异构体被鉴定为游离形式和甾醇酯形式，甾醇双键位置表明主要的细菌来源鳃甾醇[11.0% 4α-甲基-胆甾-8(14),24-二烯-3β-醇]转化为宿主胆固醇（鳃甾醇的64.2%为胆甾-5-烯-3β-醇）。鳃和外套膜制剂的稳定碳同位素值分别为：总组织-59.0和-60.4‰，总脂质-60.6和-62.4‰，磷脂脂肪酸-60.2和-63.9‰，甾醇-71.8和-73.8‰。这些稳定碳同位素值表明相对分馏模式与甲烷营养细菌纯培养实验中获得的模式相似（R.E.萨蒙斯、L.L.扬克和Z.罗克桑迪奇，《地球化学与宇宙化学学报》58: 2853 - 2863, 1994），进一步支持了细菌甲基甾醇库的转化。
