Tripartite Symbiosis of an Anaerobic Scuticociliate with Two Hydrogenosome-Associated Endosymbionts, a Holospora-Related Alphaproteobacterium and a Methanogenic Archaeon
Tripartite Symbiosis of an Anaerobic Scuticociliate with Two Hydrogenosome-Associated Endosymbionts, a Holospora-Related Alphaproteobacterium and a Methanogenic Archaeon
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DOI：
10.1128/aem.00854-19
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发表时间：
2019-10
影响因子：
4.4
通讯作者：
Kazutaka Takeshita;Takanori Yamada;Yuto Kawahara;T. Narihiro;Michihiro Ito;Y. Kamagata;N. Shinzato
中科院分区：
文献类型：
--
作者：
Kazutaka Takeshita;Takanori Yamada;Yuto Kawahara;T. Narihiro;Michihiro Ito;Y. Kamagata;N. Shinzato
厌氧纤毛原生生物与其胞内古生菌和细菌共生体之间的三方共生并不少见，但大多数报道主要基于显微观察。由于实验室培养厌氧纤毛虫的困难以及长期培养过程中原核生物伙伴的频繁丧失，对这些涉及所有三个生命领域的伙伴的迷人共生体的功能、生态和进化的更深层次的深入了解受到了阻碍。在本研究中，我们报道了一株厌氧鳞状球菌GW7的分离，该菌株在实验室中稳定培养了3年多，没有失去任何一种内共生菌。出乎意料的是，内共生体的分子特征表明，GW7的细菌伙伴与好氧纤毛虫的核内内共生体具有亲缘关系。该菌株将使未来能够对这种三方共生中的相互作用进行基因组、转录组和蛋白质组分析，并与好氧纤毛虫的内共生进行比较。摘要许多厌氧纤毛虫，即单细胞真核生物，在细胞内以产甲烷古菌和细菌为共生伙伴。虽然这种三方关系很有趣，因为每个参与者来自不同的领域，但到目前为止，培养和维护这些具有共生伙伴的寄主物种的困难扰乱了生态和功能研究。在本研究中，我们获得了一株小型厌氧盾壳菌GW7的稳定培养。通过透射电子显微镜观察和与结构域特异的探针进行荧光原位杂交，我们证明GW7的细胞质中同时存在古生菌和细菌内共生体。这些内共生菌依赖于氢小体，氢小体是在厌氧条件下产生氢和ATP的细胞器。针对原核16S rRNA基因的克隆文库分析、内共生菌特异探针的荧光原位杂交和分子系统发育分析揭示了这些内共生菌的系统发育关系和细胞内的定位。内共生考古子是一种产甲烷菌，隶属于微甲烷菌目甲烷菌属；该属的一个成员此前曾被描述为沼虾属(虫纲)的一种厌氧纤毛虫的内生菌，与GW7菌株(寡膜菌纲)仅有较远的亲缘关系。内共生菌属于甲型变形杆菌纲的大孢子科，也包括多种好氧纤毛虫的内共生菌。对于这种内共生菌，我们提出了一个新的候选属和种，即假丝酵母氢细菌内共生菌。重要性厌氧纤毛原生生物与其胞内古生菌和细菌共生体之间的三方共生并不少见，但大多数报道主要基于显微观察。由于实验室培养厌氧纤毛虫的困难以及长期培养过程中原核生物伙伴的频繁丧失，对这些涉及所有三个生命领域的伙伴的迷人共生体的功能、生态和进化的更深层次的深入了解受到了阻碍。在本研究中，我们报道了一株厌氧鳞状球菌GW7的分离，该菌株在实验室中稳定培养了3年多，没有失去任何一种内共生菌。出乎意料的是，内共生体的分子特征表明，GW7的细菌伙伴与好氧纤毛虫的核内内共生体具有亲缘关系。该菌株将使未来能够对这种三方共生中的相互作用进行基因组、转录组和蛋白质组分析，并与好氧纤毛虫的内共生进行比较。
Tripartite symbioses between anaerobic ciliated protists and their intracellular archaeal and bacterial symbionts are not uncommon, but most reports have been based mainly on microscopic observations. Deeper insights into the function, ecology, and evolution of these fascinating symbioses involving partners from all three domains of life have been hampered by the difficulties of culturing anaerobic ciliates in the laboratory and the frequent loss of their prokaryotic partners during long-term cultivation. In the present study, we report the isolation of an anaerobic scuticociliate, strain GW7, which has been stably maintained in our laboratory for more than 3 years without losing either of its endosymbionts. Unexpectedly, molecular characterization of the endosymbionts revealed that the bacterial partner of GW7 is phylogenetically related to intranuclear endosymbionts of aerobic ciliates. This strain will enable future genomic, transcriptomic, and proteomic analyses of the interactions in this tripartite symbiosis and a comparison with endosymbioses in aerobic ciliates. ABSTRACT A number of anaerobic ciliates, unicellular eukaryotes, intracellularly possess methanogenic archaea and bacteria as symbiotic partners. Although this tripartite relationship is of interest in terms of the fact that each participant is from a different domain, the difficulty in culture and maintenance of those host species with symbiotic partners has disturbed both ecological and functional studies so far. In this study, we obtained a stable culture of a small anaerobic scuticociliate, strain GW7. By transmission electron microscopic observation and fluorescent in situ hybridization with domain-specific probes, we demonstrate that GW7 possesses both archaeal and bacterial endosymbionts in its cytoplasm. These endosymbionts are in dependently associated with hydrogenosomes, which are organelle producing hydrogen and ATP under anaerobic conditions. Clone library analyses targeting prokaryotic 16S rRNA genes, fluorescent in situ hybridization with endosymbiont-specific probes, and molecular phylogenetic analyses revealed the phylogenetic affiliations and intracellular localizations of these endosymbionts. The endosymbiotic archaeon is a methanogen belonging to the genus Methanoregula (order Methanomicrobiales); a member of this genus has previously been described as the endosymbiont of an anaerobic ciliate from the genus Metopus (class Armophorea), which is only distantly related to strain GW7 (class Oligohymenophorea). The endosymbiotic bacterium belongs to the family Holosporaceae of the class Alphaproteobacteria, which also comprises several endosymbionts of various aerobic ciliates. For this endosymbiotic bacterium, we propose a novel candidate genus and species, “Candidatus Hydrogenosomobacter endosymbioticus.” IMPORTANCE Tripartite symbioses between anaerobic ciliated protists and their intracellular archaeal and bacterial symbionts are not uncommon, but most reports have been based mainly on microscopic observations. Deeper insights into the function, ecology, and evolution of these fascinating symbioses involving partners from all three domains of life have been hampered by the difficulties of culturing anaerobic ciliates in the laboratory and the frequent loss of their prokaryotic partners during long-term cultivation. In the present study, we report the isolation of an anaerobic scuticociliate, strain GW7, which has been stably maintained in our laboratory for more than 3 years without losing either of its endosymbionts. Unexpectedly, molecular characterization of the endosymbionts revealed that the bacterial partner of GW7 is phylogenetically related to intranuclear endosymbionts of aerobic ciliates. This strain will enable future genomic, transcriptomic, and proteomic analyses of the interactions in this tripartite symbiosis and a comparison with endosymbioses in aerobic ciliates.