Schuster Lukas, Bright Monika
University of Vienna, Department of Limnology and Bio-Oceanography, Althanstraße 14, A-1090 Vienna, Austria.
PLoS One. 2016 Sep 28;11(9):e0162834. doi: 10.1371/journal.pone.0162834. eCollection 2016.
Symbioses between ciliate hosts and prokaryote or unicellular eukaryote symbionts are widespread. Here, we report on a novel ciliate species within the genus Zoothamnium Bory de St. Vincent, 1824, isolated from shallow-water sunken wood in the North Adriatic Sea (Mediterranean Sea), proposed as Zoothamnium ignavum sp. nov. We found this ciliate species to be associated with a novel genus of bacteria, here proposed as "Candidatus Navis piranensis" gen. nov., sp. nov. The descriptions of host and symbiont species are based on morphological and ultrastructural studies, the SSU rRNA sequences, and in situ hybridization with symbiont-specific probes. The host is characterized by alternate microzooids on alternate branches arising from a long, common stalk with an adhesive disc. Three different types of zooids are present: microzooids with a bulgy oral side, roundish to ellipsoid macrozooids, and terminal zooids ellipsoid when dividing or bulgy when undividing. The oral ciliature of the microzooids runs 1¼ turns in a clockwise direction around the peristomial disc when viewed from inside the cell and runs into the infundibulum, where it makes another ¾ turn. The ciliature consists of a paroral membrane (haplokinety), three adoral membranelles (polykineties), and one stomatogenic kinety (germinal kinety). One circular row of barren kinetosomes is present aborally (trochal band). Phylogenetic analyses placed Z. ignavum sp. nov. within the clade II of the polyphyletic family Zoothamniidae (Oligohymenophorea). The ectosymbiont was found to occur in two different morphotypes, as rods with pointed ends and coccoid rods. It forms a monophyletic group with two uncultured Gammaproteobacteria within an unclassified group of Gammaproteobacteria, and is only distantly related to the ectosymbiont of the closely related peritrich Z. niveum (Hemprich and Ehrenberg, 1831) Ehrenberg, 1838.
纤毛虫宿主与原核生物或单细胞真核生物共生体之间的共生关系广泛存在。在此，我们报道了一种新的聚缩虫属（Zoothamnium Bory de St. Vincent，1824）纤毛虫物种，它是从亚得里亚海北部（地中海）的浅水沉没木材中分离出来的，被命名为怠惰聚缩虫（Zoothamnium ignavum）新种。我们发现这种纤毛虫物种与一种新的细菌属相关联，在此将其命名为“皮兰纳维斯念珠菌（Candidatus Navis piranensis）”新属新种。宿主和共生体物种的描述基于形态学和超微结构研究、小亚基核糖体RNA序列以及与共生体特异性探针的原位杂交。宿主的特征是在由带有附着盘的长共同柄上交替分支上有交替的微口虫。存在三种不同类型的类器官：口腔一侧鼓起的微口虫、圆形至椭圆形的大口虫以及分裂时为椭圆形或不分裂时为鼓起状的末端类器官。从细胞内部观察时，微口虫的口纤毛围绕口盘沿顺时针方向运行1¼圈，然后进入漏斗，在那里再运行¾圈。纤毛由一个口侧膜（单动列）、三个口前膜（复动列）和一个口发生动列（生殖动列）组成。在口后（轮带）有一排圆形的无纤毛基体。系统发育分析将怠惰聚缩虫新种置于多源聚缩虫科（寡膜纲）的进化枝II内。发现外共生体有两种不同的形态类型，即末端尖锐的杆状和球状杆状。它与未分类的γ-变形菌门中的两种未培养的γ-变形菌形成一个单系群，并且与密切相关的周丛生怠惰聚缩虫（Hemprich和Ehrenberg，1831）Ehrenberg，1838的外共生体关系较远。
