School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98195, USA.
Microb Ecol. 2012 Nov;64(4):1064-72. doi: 10.1007/s00248-012-0080-4. Epub 2012 Jun 24.
Studies on the ecology of microbial parasites and their hosts are predicated on understanding the assemblage of and relationship among the species present. Changes in organismal morphology and physiology can have profound effects on host-parasite interactions and associated microbial community structure. The marine rickettsial organism, "Candidatus Xenohaliotis californiensis" (WS-RLO), that causes withering syndrome of abalones has had a consistent morphology based on light and electron microscopy. However, a morphological variant of the WS-RLO has recently been observed infecting red abalone from California. We used light and electron microscopy, in situ hybridization and16S rDNA sequence analysis to compare the WS-RLO and the morphologically distinct RLO variant (RLOv). The WS-RLO forms oblong inclusions within the abalone posterior esophagus (PE) and digestive gland (DG) tissues that contain small rod-shaped bacteria; individual bacteria within the light purple inclusions upon hematoxylin and eosin staining cannot be discerned by light microscopy. Like the WS-RLO, the RLOv forms oblong inclusions in the PE and DG but contain large, pleomorphic bacteria that stain dark navy blue with hematoxylin and eosin. Transmission electron microscopy (TEM) examination revealed that the large pleomorphic bacteria within RLOv inclusions were infected with a spherical to icosahedral-shaped putative phage hyperparasite. TEM also revealed the presence of rod-shaped bacteria along the periphery of the RLOv inclusions that were morphologically indistinguishable from the WS-RLO. Binding of the WS-RLO-specific in situ hybridization probe to the RLOv inclusions demonstrated sequence similarity between these RLOs. In addition, sequence analysis revealed 98.9-99.4 % similarity between 16S rDNA sequences of the WS-RLO and RLOv. Collectively, these data suggest that both of these RLOs infecting California abalone are "Candidatus Xenohaliotis californiensis," and that the novel variant is infected by a putative phage hyperparasite that induced morphological variation of its RLO host.
对微生物寄生虫及其宿主的生态学研究，是以了解现有物种的组合和相互关系为前提的。生物体形态和生理的变化会对宿主-寄生虫相互作用和相关微生物群落结构产生深远影响。引起鲍鱼枯萎综合征的海洋立克次体生物“加利福尼亚拟 Xenohaliotis californiensis”（WS-RLO）基于光镜和电子显微镜一直具有一致的形态。然而，最近在加利福尼亚的红鲍中观察到了一种 WS-RLO 的形态变异体（RLOv）。我们使用光镜和电子显微镜、原位杂交和 16S rDNA 序列分析来比较 WS-RLO 和形态明显不同的 RLO 变体（RLOv）。WS-RLO 在鲍鱼后肠（PE）和消化腺（DG）组织内形成长形内含物，内含物中含有小杆状细菌；苏木精和曙红染色的浅紫色内含物中的单个细菌用光镜无法分辨。与 WS-RLO 一样，RLOv 在 PE 和 DG 中形成长形内含物，但内含物中含有大型、多形细菌，用苏木精和曙红染色呈深蓝色。透射电子显微镜（TEM）检查显示，RLOv 内含物中的大型多形细菌被一种球形到二十面体形状的假定噬菌体超寄生菌感染。TEM 还显示，在 RLOv 内含物的周边存在形态上与 WS-RLO 无法区分的杆状细菌。WS-RLO 特异性原位杂交探针与 RLOv 内含物的结合表明这些 RLO 之间存在序列相似性。此外，16S rDNA 序列分析显示 WS-RLO 和 RLOv 之间的序列相似性为 98.9-99.4%。综上所述，感染加利福尼亚鲍的这两种 RLO 都是“加利福尼亚拟 Xenohaliotis californiensis”，而新型变体被一种假定的噬菌体超寄生菌感染，导致其 RLO 宿主发生形态变异。
