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Bodo saltans (Kinetoplastida) is dependent on a novel Paracaedibacter -like endosymbiont that possesses multiple putative toxin-antitoxin systems
The ISME Journal ( IF 11.0 ) Pub Date : 2021-01-15 , DOI: 10.1038/s41396-020-00879-6
Samriti Midha 1 , Daniel J Rigden 2 , Stefanos Siozios 1 , Gregory D D Hurst 1 , Andrew P Jackson 1
Affiliation  

Bacterial endosymbiosis has been instrumental in eukaryotic evolution, and includes both mutualistic, dependent and parasitic associations. Here we characterize an intracellular bacterium inhabiting the flagellated protist Bodo saltans (Kinetoplastida). We present a complete bacterial genome comprising a 1.39 Mb circular chromosome with 40.6% GC content. Fluorescent in situ hybridisation confirms that the endosymbiont is located adjacent to the nuclear membrane, and a detailed model of its intracellular niche is generated using serial block-face scanning electron microscopy. Phylogenomic analysis shows that the endosymbiont belongs to the Holosporales, most closely related to other α-proteobacterial endosymbionts of ciliates and amoebae. Comparative genomics indicates that it has a limited metabolism and is nutritionally host-dependent. However, the endosymbiont genome does encode diverse symbiont-specific secretory proteins, including a type VI secretion system and three separate toxin-antitoxin systems. We show that these systems are actively transcribed and hypothesize they represent a mechanism by which B. saltans becomes addicted to its endosymbiont. Consistent with this idea, attempts to cure Bodo of endosymbionts led to rapid and uniform cell death. This study adds kinetoplastid flagellates to ciliates and amoebae as hosts of Paracaedibacter-like bacteria, suggesting that these antagonistic endosymbioses became established very early in Eukaryotic evolution.



中文翻译:

Bodo saltans (Kinetoplastida) 依赖于一种新型副杆菌样内共生体,该内共生体拥有多个假定的毒素-抗毒素系统

细菌内共生在真核进化中发挥了重要作用,包括互惠、依赖和寄生关联。在这里,我们描述了一种居住在有鞭毛原生生物Bodo saltans(Kinetoplastida)的细胞内细菌。我们提出了一个完整的细菌基因组,包含 1.39 Mb 的环状染色体,GC 含量为 40.6%。荧光原位杂交证实内共生体位于核膜附近,并使用串行块面扫描电子显微镜生成其细胞内生态位的详细模型。系统基因组分析表明,该内共生菌属于全孢菌目,与纤毛虫和变形虫的其他α-变形菌内共生菌关系最密切。比较基因组学表明它的新陈代谢有限并且具有营养宿主依赖性。然而,内共生体基因组确实编码多种共生体特异性分泌蛋白,包括 VI 型分泌系统和三个独立的毒素-抗毒素系统。我们证明这些系统是活跃转录的,并假设它们代表了B. saltans对其内共生体上瘾的机制。与这个想法一致的是,治愈内共生体博多的尝试导致了细胞快速而均匀的死亡。这项研究将动质体鞭毛虫添加到纤毛虫和变形虫中,作为类副藻类细菌的宿主,这表明这些拮抗性内共生在真核进化的早期就已经建立。

更新日期:2021-01-16
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