Cellular and Molecular Life Sciences ( IF 8 ) Pub Date : 2020-02-01 , DOI: 10.1007/s00018-020-03462-6 István Zachar 1, 2, 3 , Gergely Boza 1, 4
Endosymbiosis and organellogenesis are virtually unknown among prokaryotes. The single presumed example is the endosymbiogenetic origin of mitochondria, which is hidden behind the event horizon of the last eukaryotic common ancestor. While eukaryotes are monophyletic, it is unlikely that during billions of years, there were no other prokaryote–prokaryote endosymbioses as symbiosis is extremely common among prokaryotes, e.g., in biofilms. Therefore, it is even more precarious to draw conclusions about potentially existing (or once existing) prokaryotic endosymbioses based on a single example. It is yet unknown if the bacterial endosymbiont was captured by a prokaryote or by a (proto-)eukaryote, and if the process of internalization was parasitic infection, slow engulfment, or phagocytosis. In this review, we accordingly explore multiple mechanisms and processes that could drive the evolution of unicellular microbial symbioses with a special attention to prokaryote–prokaryote interactions and to the mitochondrion, possibly the single prokaryotic endosymbiosis that turned out to be a major evolutionary transition. We investigate the ecology and evolutionary stability of inter-species microbial interactions based on dependence, physical proximity, cost–benefit budget, and the types of benefits, investments, and controls. We identify challenges that had to be conquered for the mitochondrial host to establish a stable eukaryotic lineage. Any assumption about the initial interaction of the mitochondrial ancestor and its contemporary host based solely on their modern relationship is rather perilous. As a result, we warn against assuming an initial mutually beneficial interaction based on modern mitochondria–host cooperation. This assumption is twice fallacious: (i) endosymbioses are known to evolve from exploitative interactions and (ii) cooperativity does not necessarily lead to stable mutualism. We point out that the lack of evidence so far on the evolution of endosymbiosis from mutual syntrophy supports the idea that mitochondria emerged from an exploitative (parasitic or phagotrophic) interaction rather than from syntrophy.
中文翻译:
真核生物之前的内共生:原核生物中的线粒体建立。
内生共生和器官发生在原核生物中实际上是未知的。单个推测的例子是线粒体的内生遗传起源,它隐藏在最后一个真核共同祖先的事件视野之后。尽管真核生物是单系的,但在数十亿年内不可能再没有其他原核生物-原核内共生酶,因为共生在原核生物中极为常见,例如在生物膜中。因此,根据一个例子得出关于潜在存在的(或一旦存在的)原核内共生酶的结论就更加不稳定。尚不知道细菌内共生菌是被原核生物还是被(原核)真核生物捕获,并且内在化过程是寄生虫感染,缓慢吞噬还是吞噬作用。在这篇评论中 因此,我们探索了多种可能驱动单细胞微生物共生体进化的机制和过程,并特别关注原核生物-原核生物相互作用和线粒体,可能是原核内共生的一个原本是主要的进化过渡。我们基于依赖关系,物理接近性,成本效益预算以及收益,投资和控制的类型,研究了物种间微生物相互作用的生态和进化稳定性。我们确定线粒体宿主建立稳定的真核细胞系所必须克服的挑战。仅基于线粒体祖先与其现代宿主之间的现代关系的任何初始假设都是相当危险的。结果是,我们警告不要基于现代的线粒体-宿主合作关系进行初始的互惠互动。这个假设是错误的两次:i)内共生酶是从剥削性相互作用演变而来的,并且(ii)合作性不一定导致稳定的共存。我们指出,到目前为止,关于相互共生的内共生进化的证据尚缺乏,这支持了线粒体是由剥削(寄生或吞噬)相互作用而非共生形成的观点。