Kochi Institute for Core Sample Research, Japan Agency for Earth-Marine Science and Technology (JAMSTEC), Nankoku, Kochi 783-8502, Japan.
Proc Natl Acad Sci U S A. 2011 Nov 8;108(45):18295-300. doi: 10.1073/pnas.1107763108. Epub 2011 Oct 10.
Remarkable numbers of microbial cells have been observed in global shallow to deep subseafloor sediments. Accumulating evidence indicates that deep and ancient sediments harbor living microbial life, where the flux of nutrients and energy are extremely low. However, their physiology and energy requirements remain largely unknown. We used stable isotope tracer incubation and nanometer-scale secondary ion MS to investigate the dynamics of carbon and nitrogen assimilation activities in individual microbial cells from 219-m-deep lower Pleistocene (460,000 y old) sediments from the northwestern Pacific off the Shimokita Peninsula of Japan. Sediment samples were incubated in vitro with (13)C- and/or (15)N-labeled glucose, pyruvate, acetate, bicarbonate, methane, ammonium, and amino acids. Significant incorporation of (13)C and/or (15)N and growth occurred in response to glucose, pyruvate, and amino acids (∼76% of total cells), whereas acetate and bicarbonate were incorporated without fostering growth. Among those substrates, a maximum substrate assimilation rate was observed at 67 × 10(-18) mol/cell per d with bicarbonate. Neither carbon assimilation nor growth was evident in response to methane. The atomic ratios between nitrogen incorporated from ammonium and the total cellular nitrogen consistently exceeded the ratios of carbon, suggesting that subseafloor microbes preferentially require nitrogen assimilation for the recovery in vitro. Our results showed that the most deeply buried subseafloor sedimentary microbes maintain potentials for metabolic activities and that growth is generally limited by energy but not by the availability of C and N compounds.
在全球浅至深海海底沉积物中已经观察到大量的微生物细胞。越来越多的证据表明，深且古老的沉积物中存在着有生命的微生物，那里的营养物质和能量通量极低。然而，它们的生理学和能量需求在很大程度上仍然未知。我们使用稳定同位素示踪剂孵育和纳米级二次离子 MS，来研究来自日本下北半岛西北太平洋的 219 米深的更新世下部（46 万年）沉积物中单个微生物细胞的碳和氮同化活性的动态。用（13）C-和/或（15）N 标记的葡萄糖、丙酮酸盐、乙酸盐、碳酸氢盐、甲烷、铵和氨基酸体外孵育沉积物样品。葡萄糖、丙酮酸盐和氨基酸（约 76%的总细胞）显著促进了（13）C 和/或（15）N 的掺入和生长，而乙酸盐和碳酸氢盐的掺入没有促进生长。在这些底物中，碳酸氢盐的最大底物同化率为 67×10(-18) mol/细胞/天。甲烷没有引起碳同化或生长。从铵中掺入的氮与总细胞氮的原子比始终超过碳的比值，这表明海底微生物优先需要氮同化来进行体外恢复。我们的结果表明，埋藏最深的海底沉积物微生物保持代谢活性的潜力，并且生长通常受到能量的限制，而不是 C 和 N 化合物的可利用性的限制。
