Martin William F, Tielens Aloysius G M, Mentel Marek, Garg Sriram G, Gould Sven B
Institute for Molecular Evolution, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
Microbiol Mol Biol Rev. 2017 Jun 14;81(3). doi: 10.1128/MMBR.00008-17. Print 2017 Sep.
How mitochondria came to reside within the cytosol of their host has been debated for 50 years. Though current data indicate that the last eukaryote common ancestor possessed mitochondria and was a complex cell, whether mitochondria or complexity came first in eukaryotic evolution is still discussed. In autogenous models (complexity first), the origin of phagocytosis poses the limiting step at eukaryote origin, with mitochondria coming late as an undigested growth substrate. In symbiosis-based models (mitochondria first), the host was an archaeon, and the origin of mitochondria was the limiting step at eukaryote origin, with mitochondria providing bacterial genes, ATP synthesis on internalized bioenergetic membranes, and mitochondrion-derived vesicles as the seed of the eukaryote endomembrane system. Metagenomic studies are uncovering new host-related archaeal lineages that are reported as complex or phagocytosing, although images of such cells are lacking. Here we review the physiology and components of phagocytosis in eukaryotes, critically inspecting the concept of a phagotrophic host. From ATP supply and demand, a mitochondrion-lacking phagotrophic archaeal fermenter would have to ingest about 34 times its body weight in prokaryotic prey to obtain enough ATP to support one cell division. It would lack chemiosmotic ATP synthesis at the plasma membrane, because phagocytosis and chemiosmosis in the same membrane are incompatible. It would have lived from amino acid fermentations, because prokaryotes are mainly protein. Its ATP yield would have been impaired relative to typical archaeal amino acid fermentations, which involve chemiosmosis. In contrast, phagocytosis would have had great physiological benefit for a mitochondrion-bearing cell.
线粒体是如何进入其宿主细胞溶胶的，这一问题已经争论了50年。尽管目前的数据表明，最后一个真核生物共同祖先拥有线粒体，是一个复杂细胞，但在真核生物进化中，线粒体还是复杂性先出现，这一问题仍在讨论中。在自生模型（复杂性先出现）中，吞噬作用的起源是真核生物起源的限制步骤，线粒体作为未被消化的生长底物出现得较晚。在基于共生的模型（线粒体先出现）中，宿主是古菌，线粒体的起源是真核生物起源的限制步骤，线粒体提供细菌基因、内化生物能膜上的ATP合成，以及线粒体衍生的囊泡作为真核生物内膜系统的种子。宏基因组研究正在发现新的与宿主相关的古菌谱系，这些谱系被报道为复杂或具有吞噬作用，尽管缺乏此类细胞的图像。在这里，我们回顾了真核生物吞噬作用的生理学和组成部分，批判性地审视了吞噬营养宿主的概念。从ATP的供需来看，一个缺乏线粒体的吞噬营养古菌发酵体必须摄取其体重约34倍的原核猎物，才能获得足够的ATP来支持一次细胞分裂。它在质膜上缺乏化学渗透ATP合成，因为吞噬作用和同一膜上的化学渗透是不相容的。它可能依靠氨基酸发酵生存，因为原核生物主要是蛋白质。相对于典型的涉及化学渗透的古菌氨基酸发酵，其ATP产量会受到损害。相比之下，吞噬作用对含有线粒体的细胞具有巨大的生理益处。
