纳米细菌是一种形似细胞的微小颗粒，直径可小至80纳米，只能通过电子显微镜观察，且广泛存在于各种生物体和非生物体中。人们一直怀疑它是生物，原因是：纳米细菌往往形似正在分裂的细胞；而且其周围可聚集羟磷灰石———动物骨骼中的主要成分，这被认为是纳米细菌繁殖的可能方式。那么，纳米细菌是活的吗？属不属于生物范畴？中国台湾成功大学和美国洛克菲勒大学的科学家在《美国国家科学院院刊》上发表论文称，基于DNA繁殖模式的生物最小直径要在200纳米以上，所以纳米细菌并非生物。
研究人员通过一系列实验发现：健康人类血清中的纳米细菌以复合碳酸钙为成分，不包含DNA或RNA的痕迹，应该不是以生物方式生成的。之前研究也有类似看法，但没有给出纳米细菌的化学构成。此次则提出了一个纳米细菌生长的化学模型，根据这一假说，人们能通过改变碳酸钙沉淀所需的基质，去控制纳米细菌生长的速度和形状。
科学家还发现，羟磷灰石只在特定状态下，比如与抑制晶体生长蛋白质混合时，才聚集在纳米细菌周围，说明羟磷灰石并非纳米细菌生长所必需。
研究人员之一，洛克菲勒大学的约翰?扬说：“纳米细菌曾有望成为地球上最小的细胞形式，并解释地球和地外细胞生命的起源。但我们的成果明确否认了纳米细菌是活的有机体。”之前的有关研究曾暗示，纳米细菌是引起肾病和动脉硬化症等许多疾病的病原体。约翰?扬并未否定这种可能性，但他认为尚缺乏充分证据。
生物谷推荐原始出处：
PNAS 2008 105: 5549-5554; published online on April 2, 2008, 10.1073/pnas.0711744105
Purported nanobacteria in human blood as calcium carbonate nanoparticles
Jan Martel*, and John Ding-E Young
*Department of Biochemistry and Cellular Molecular Biology, Chang Gung University, 259 Wen-Hua First Road, Kwei-Shan, Tao-Yuan 333, Taiwan, Republic of China; and Department of Cellular Physiology and Immunology, The Rockefeller University, New York, NY 10021
Edited by Norman R. Pace, University of Colorado, Boulder, CO, and approved February 29, 2008 (received for review December 13, 2007)
Recent evidence suggests a role for nanobacteria in a growing number of human diseases, including renal stone formation, cardiovascular diseases, and cancer. This large body of research studies promotes the view that nanobacteria are not only alive but that they are associated with disease pathogenesis. However, it is still unclear whether they represent novel life forms, overlooked nanometer-size bacteria, or some other primitive self-replicating microorganisms. Here, we report that CaCO3 precipitates prepared in vitro are remarkably similar to purported nanobacteria in terms of their uniformly sized, membrane-delineated vesicular shapes, with cellular division-like formations and aggregations in the form of colonies. The gradual appearance of nanobacteria-like particles in incubated human serum as well as the changes seen with their size and shape can be influenced and explained by introducing varying levels of CO2 and NaHCO3 as well as other conditions known to influence the precipitation of CaCO3. Western blotting reveals that the monoclonal antibodies, claimed to be specific for nanobacteria, react in fact with serum albumin. Furthermore, nanobacteria-like particles obtained from human blood are able to withstand high doses of -irradiation up to 30 kGy, and no bacterial DNA is found by performing broad-range PCR amplifications. Collectively, our results provide a more plausible abiotic explanation for the unusual properties of purported nanobacteria.
