Molecular and Environmental Toxicology Program, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
PLoS One. 2011;6(6):e20725. doi: 10.1371/journal.pone.0020725. Epub 2011 Jun 7.
Bacterial outer membrane vesicles (OMV) are packets of periplasmic material that, via the proteins and other molecules they contain, project metabolic function into the environment. While OMV production is widespread in proteobacteria, they have been extensively studied only in pathogens, which inhabit fully hydrated environments. However, many (arguably most) bacterial habitats, such as soil, are only partially hydrated. In the latter, water is characteristically distributed as films on soil particles that are, on average thinner, than are typical OMV (ca. ≤10 nm water film vs. 20 to >200 nm OMV;).
METHODOLOGY/PRINCIPAL FINDINGS: We have identified a new bacterial surface structure, termed a "nanopod", that is a conduit for projecting OMV significant distances (e.g., ≥6 µm) from the cell. Electron cryotomography was used to determine nanopod three-dimensional structure, which revealed chains of vesicles within an undulating, tubular element. By using immunoelectron microscopy, proteomics, heterologous expression and mutagenesis, the tubes were determined to be an assembly of a surface layer protein (NpdA), and the interior structures identified as OMV. Specific metabolic function(s) for nanopods produced by Delftia sp. Cs1-4 are not yet known. However, a connection with phenanthrene degradation is a possibility since nanopod formation was induced by growth on phenanthrene. Orthologs of NpdA were identified in three other genera of the Comamonadaceae family, and all were experimentally verified to form nanopods.
CONCLUSIONS/SIGNIFICANCE: Nanopods are new bacterial organelles, and establish a new paradigm in the mechanisms by which bacteria effect long-distance interactions with their environment. Specifically, they create a pathway through which cells can effectively deploy OMV, and the biological activity these transmit, in a diffusion-independent manner. Nanopods would thus allow environmental bacteria to expand their metabolic sphere of influence in a manner previously unknown for these organisms.
细菌外膜囊泡（OMV）是一种包含周质物质的囊泡，通过其中包含的蛋白质和其他分子，将代谢功能投射到环境中。虽然 OMV 的产生在变形菌中很普遍，但它们仅在病原体中得到了广泛研究，这些病原体生活在完全水合的环境中。然而，许多（可以说大多数）细菌栖息地，如土壤，只是部分水合的。在后一种情况下，水的特征分布是在土壤颗粒上的薄膜，这些薄膜的平均厚度比典型的 OMV 薄（约 10nm 水膜与 20 至>200nm 的 OMV 相比；）。
方法/主要发现：我们已经确定了一种新的细菌表面结构，称为“纳米足”，它是将 OMV 从细胞中显著投射的通道，距离可达 6μm 以上。电子 cryotomography 用于确定纳米足的三维结构，结果显示囊泡在波浪形管状元件内形成链。通过使用免疫电子显微镜、蛋白质组学、异源表达和诱变，确定这些管是表面层蛋白（NpdA）的组装体，内部结构被鉴定为 OMV。目前还不知道 Delftia sp. Cs1-4 产生的纳米足的具体代谢功能。然而，与菲降解的联系是一种可能性，因为在菲生长时诱导了纳米足的形成。NpdA 的同源物在 Comamonadaceae 家族的另外三个属中被鉴定出来，并且所有这些都通过实验验证形成了纳米足。
结论/意义：纳米足是新的细菌细胞器，为细菌与环境进行长距离相互作用的机制建立了一个新的范例。具体来说，它们创建了一种途径，通过该途径，细胞可以以非扩散依赖的方式有效地部署 OMV 和这些传递的生物活性。因此，纳米足可以使环境细菌以这些生物体以前未知的方式扩大其代谢影响范围。
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