日本海洋研究开发机构日前宣布，其研究小组在青森县八户市近海海底距今约46万年前的地层中采集到大量活的“超节能”微生物。由于这些微生物消耗能量的速度极慢，研究人员推测这些生物已在严酷的环境中生存了数百年甚至数千年以上。
研究小组2006年利用“地球”号深海探测船对八户市约80公里外近海水深约1200米的海底进行了钻探。结果在海底以下约200米、距今约46万年前的地层中发现每立方厘米含有超过1000万个单细胞微生物，并对这些微生物进行了培养。
这些微生物多数都是未知的，大小只有0.5至1微米。研究人员向这些微生物提供养分后，利用高性能的质量分析仪进行检测，发现约80％的养分被吸收，从而确认这些微生物是活的。
研究小组发现，如果向这些微生物投放葡萄糖等高营养物质，细胞还会分裂并增殖。不过，这些微生物吸收养分的速度不到大肠杆菌的十万分之一，极为缓慢。研究人员根据它们吸收和消耗能量的速度估算认为，这些微生物可能活了数百到数千年。
海洋研究开发机构首席研究员诸野祐树指出，这一发现将有助于弄清微生物参与的甲烷水合物和天然气等形成的原因。
这一成果已刊登在最新一期的美国《国家科学院院刊》（PNAS）网络版上。（生物谷 Bioon.com）
doi:10.1073/pnas.1107763108
PMC:
PMID:
Carbon and nitrogen assimilation in deep subseafloor microbial cells
Morono, Yuki; Terada, Takeshi; Nishizawa, Manabu; Ito, Motoo; Hillion, Fran?ois; Takahata, Naoto; Sano, Yuji; Inagaki, Fumio
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 13C- and/or 15N-labeled glucose, pyruvate, acetate, bicarbonate, methane, ammonium, and amino acids. Significant incorporation of 13C and/or 15N 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.
