Lipid biomarkers of shelf sediments from upwelling regions off Namibia, Peru, and Chile

Sediments of upwelling regions off Namibia, Peru, and Chile contain dense populations of large nitrate-storing sulfide-oxidizing bacteria, Thiomargarita, Beggiatoa, and Thioploca. Increased contents of monounsaturated C16 and C18 fatty acids have been found at all stations studied, especially when a high density of sulfide oxidizers in the sediments was observed. The distribution of lipid biomarkers attributed to sulfate reducers (10MeC16:0 fatty acid, ai-C15:0 fatty acid, and mono-O-alkyl glycerol ethers) compared to the distribution of sulfide oxidizers indicate a close association between these bacteria. As a consequence, the distributions of sulfate reducers in sediments of Namibia, Peru, and Chile are closely related to differences in the motility of the various sulfide oxidizers at the three study sites. Depth profiles of mono-O-alkyl glycerol ethers have been found to correlate best with the occurrence of large sulfide-oxidizing bacteria. This suggests a particularly close link between mono-O-alkyl glycerol ether-synthesizing sulfate reducers and sulfide oxidizers. The interaction between sulfide-oxidizing bacteria and sulfate-reducing bacteria reveals intense sulfur cycling and degradation of organic matter in different sediment depths.纳米比亚、秘鲁与智利沿岸上升流区的沉积物中，栖息着高密度的大型硝酸盐储存型氧化硫化物细菌，包括嗜硫珠菌属（Thiomargarita）、贝氏硫菌属（Beggiatoa）及管丝硫细菌属（Thioploca）。所有研究站位均观测到单不饱和C16及C18脂肪酸含量升高的现象，且该现象与沉积物中氧化硫化物细菌的高密度分布显著相关。针对以10MeC16:0脂肪酸、反异-C15:0脂肪酸及单-O-烷基甘油醚（mono-O-alkyl glycerol ethers）为标识的硫酸盐还原菌（sulfate reducers），其脂类生物标志物（lipid biomarkers）的分布模式与氧化硫化物细菌的分布对比分析显示，两类细菌之间存在紧密的共生关联。由此可知，纳米比亚、秘鲁和智利沿岸沉积物中硫酸盐还原菌的分布，与三个研究区域内各类氧化硫化物细菌的运动能力差异密切相关。研究发现，单-O-烷基甘油醚的深度分布与大型氧化硫化物细菌的出现情况相关性最强。这表明合成单-O-烷基甘油醚的硫酸盐还原菌与氧化硫化物细菌之间存在尤为密切的联系。氧化硫化物细菌与硫酸盐还原菌之间的相互作用，揭示了不同沉积物深度下强烈的硫循环过程与有机质降解活动。