南海冷泉活动区双壳类生物中单不饱和脂肪酸双键位置的确定及其意义

Determination of double bond position in monounsaturated fatty acid in bivalves in active cold seeps of South China Sea and its significance

本次研究对南海冷泉活动区福尔摩沙脊(F站位)、海马冷泉环境中与甲烷有氧氧化菌共生的贻贝(分别为Bathymodiolus platifrons和Gigantidas haimaensis),以及与硫氧化菌共生的蛤(Archivesica marissinica)腮组织中的单不饱和脂肪酸进行了结构鉴定。结果发现,贻贝鳃组织中存在C16∶1ω9、C16∶1ω8和C18∶1ω8脂肪酸,同时C16∶1ω8的含量远远高于C18∶1ω8,这说明与贻贝共生的为Ⅰ型甲烷有氧氧化菌。在蛤腮组织中,单不饱和脂肪酸C16∶1ω7、C18∶1ω7和C20∶1ω7含量极高,表明ω7脂肪酸来源于硫氧化菌。同时,贻贝和蛤鳃中含有大量多不饱和脂肪酸,如C20∶2和C22∶2。在同一样品中来源于共生菌的单不饱和脂肪酸和来源于宿主的多不饱和脂肪酸具有相近的δ13C值,表明宿主从共生菌或共生菌代谢产物中获得碳源和营养。Ⅰ型甲烷有氧氧化菌在贻贝腮组织中广泛存在,指示F站位和海马冷泉活动区冷泉流体渗漏强度较弱。确定单不饱和脂肪酸的类型是判断双壳共生菌种类的基础。双壳类共生菌类型的识别,可以帮助理解共生体与宿主之间碳源和能量的转化关系、冷泉环境中甲烷的消耗过程如碳同化途径、碳循环等。

In this study,the structures of monounsaturated fatty acids were analyzed in gill tissues of two mussels(B.platifrons and G.haimaensis)and one clam(A.marissinica),symbiotic with methanotrophic and thiotrophic bacteria,respectively.The results showed that C16∶1ω9,C16∶1ω8,and C18∶1ω8 were present in the gill tissues of both mussels,and the content of C16:1ω8 was much higher than that of C18∶1ω8,indicating that type I methanotrophic bacteria were predominant in the gill tissues of mussels.In the clam gill tissue,the content of monounsaturated fatty acids C16∶1ω7,C18∶1ω7,and C20∶1ω7 were extremely high,indicating the presence of thiotrophic bacteria.At the same time,mussel and clam gill tissues contained a large amount of polyunsaturated fatty acids,such as C20∶2 and C22∶2.In the same sample,the monounsaturated fatty acids derived from symbiotic bacteria and the polyunsaturated fatty acids of the host exhibited similarδ13C values,which suggests the host obtained nutrition either directly from the symbionts or from symbiont-derived carbon.Type I methanotrophic bacteria were widely found in mussel gill tissues,indicating that cold spring fluid leakage intensities are weak at both site F and Haima seeps.Identifying the type of monounsaturated fatty acid is the foundation for identifying the type of symbiont bacteria in bivalves.Moreover,the study of carbon assimilation pathways,carbon cycling,and transformation between symbionts and hosts will contribute to the understanding of methane consumption under aerobic methane oxidation.