Ingalls Anitra E, Shah Sunita R, Hansman Roberta L, Aluwihare Lihini I, Santos Guaciara M, Druffel Ellen R M, Pearson Ann
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA.
Proc Natl Acad Sci U S A. 2006 Apr 25;103(17):6442-7. doi: 10.1073/pnas.0510157103. Epub 2006 Apr 13.
An ammonia-oxidizing, carbon-fixing archaeon, Candidatus "Nitrosopumilus maritimus," recently was isolated from a salt-water aquarium, definitively confirming that chemoautotrophy exists among the marine archaea. However, in other incubation studies, pelagic archaea also were capable of using organic carbon. It has remained unknown what fraction of the total marine archaeal community is autotrophic in situ. If archaea live primarily as autotrophs in the natural environment, a large ammonia-oxidizing population would play a significant role in marine nitrification. Here we use the natural distribution of radiocarbon in archaeal membrane lipids to quantify the bulk carbon metabolism of archaea at two depths in the subtropical North Pacific gyre. Our compound-specific radiocarbon data show that the archaea in surface waters incorporate modern carbon into their membrane lipids, and archaea at 670 m incorporate carbon that is slightly more isotopically enriched than inorganic carbon at the same depth. An isotopic mass balance model shows that the dominant metabolism at depth indeed is autotrophy (83%), whereas heterotrophic consumption of modern organic carbon accounts for the remainder of archaeal biomass. These results reflect the in situ production of the total community that produces tetraether lipids and are not subject to biases associated with incubation and/or culture experiments. The data suggest either that the marine archaeal community includes both autotrophs and heterotrophs or is a single population with a uniformly mixotrophic metabolism. The metabolic and phylogenetic diversity of the marine archaea warrants further exploration; these organisms may play a major role in the marine cycles of nitrogen and carbon.
一种氨氧化、固碳古菌，“暂定嗜盐硝化球菌”（Candidatus "Nitrosopumilus maritimus"），最近从一个海水水族箱中分离出来，这明确证实了海洋古菌中存在化学自养现象。然而，在其他培养研究中，海洋古菌也能够利用有机碳。目前仍不清楚在原位海洋古菌群落中自养型古菌占总群落的比例是多少。如果古菌在自然环境中主要以自养型生存，那么大量的氨氧化种群将在海洋硝化作用中发挥重要作用。在此，我们利用古菌膜脂中放射性碳的自然分布，来量化亚热带北太平洋环流两个深度处古菌的整体碳代谢情况。我们的化合物特异性放射性碳数据表明，表层水体中的古菌将现代碳纳入其膜脂中，而在670米深处的古菌纳入的碳，其同位素富集程度略高于同一深度的无机碳。一个同位素质量平衡模型表明，在该深度处古菌的主要代谢方式确实是自养（83%），而现代有机碳的异养消耗占古菌生物量的其余部分。这些结果反映了产生四醚脂类的整个群落的原位生产情况，且不受与培养和/或培养实验相关的偏差影响。数据表明，要么海洋古菌群落既包括自养型也包括异养型，要么是一个具有统一兼养代谢的单一群体。海洋古菌的代谢和系统发育多样性值得进一步探索；这些生物可能在海洋氮和碳循环中发挥重要作用。
