Geochemistry, microbiology and phospholipid fatty acid content of ODP Site 169-1036 sediments

Phospholipid fatty acids were measured in samples of 60°-130°C sediment taken from three holes at Site 1036 (Ocean Drilling Program Leg 169) to determine microbial community structure and possible community replacement at high temperatures. Five of six samples had similar concentrations of phospholipid fatty acids (2-6 pmol/g dry weight of sediment), and biomass estimates from these measurements compare favorably with direct microscopic counts, lending support to previous microscopic measures of deep sedimentary biomass. Very long-chain phospholipid fatty acids (21 to 30 carbons) were detected in the sediment and were up to half the total phospholipid fatty acid measured; they appear to increase in abundance with temperature, but their significance is not known. Community composition from lipid analysis showed that samples contained standard eubacterial membrane lipids but no detectable archaeal lipids, though archaea would be expected to dominate the samples at high temperatures. Cluster analysis of Middle Valley phospholipid fatty acid compositions shows that lipids in Middle Valley sediment samples are similar to each other at all temperatures, with the exception of very long-chain fatty acids. The data neither support nor deny a shift to a high-temperature microbial community in hot cores, so at the present time we cannot draw conclusions about whether the microbes observed in these hot sediments are active.本研究对大洋钻探计划（Ocean Drilling Program）第169航次1036站位3个钻孔采集的60℃~130℃沉积物样品中的磷脂脂肪酸（phospholipid fatty acids）进行了测定，旨在解析高温环境下的微生物群落结构及其潜在的群落更替过程。6份供试样品中的5份磷脂脂肪酸浓度相近，介于2~6皮摩尔每克干沉积物之间；基于该测定结果得到的生物量估算值与直接显微计数结果吻合度较高，为此前针对深层沉积生物量的显微计数研究提供了有力佐证。研究在沉积物中检测到碳链长度为21~30的超长链磷脂脂肪酸，其占总检测磷脂脂肪酸的比例最高可达50%；该类脂肪酸的相对丰度似乎随温度升高而增加，但其生态意义仍不明确。脂类分析得到的群落组成结果显示，样品中仅含有典型的真细菌细胞膜脂类，未检出古菌脂类——尽管理论上高温环境中古菌应占据群落主导地位。对中谷（Middle Valley）沉积物磷脂脂肪酸组成的聚类分析表明，除超长链脂肪酸外，中谷各温度梯度沉积物样品的脂类组成整体相似。现有数据既无法证实也无法否定热沉积柱中存在向高温微生物群落的转变过程，因此目前尚无法确定在这些热沉积物中观测到的微生物是否具有代谢活性。