Development, life cycle, ultrastructure and phylogenetic position of Pasteuria ramosa Metchnikoff 1888: Rediscovery of an obligate endoparasite of Daphnia magna Straus
Development, life cycle, ultrastructure and phylogenetic position of Pasteuria ramosa Metchnikoff 1888: Rediscovery of an obligate endoparasite of Daphnia magna Straus
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DOI：
10.1098/rstb.1996.0151
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发表时间：
1996-12-29
期刊：
影响因子：
--
通讯作者：
Scholz, D
中科院分区：
文献类型：
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作者：
Ebert, D;Rainey, P;Scholz, D
描述了大型水蚤专性内寄生虫的发育、生活史、超微结构和系统发育地位。1992-1994年在英国和俄罗斯采集的3种大型水蚤(D.Magna、D.Pulex和D.Longispina)的体腔内发现了微寄生虫，并通过与大型水蚤共培养的方式维持在人工养殖中。内寄生虫的传播是通过从死亡的受感染宿主遗体释放的水生孢子水平进行的。感染宿主的后代从未被感染，表明没有发生垂直传播。受感染的母亲在感染后不久停止产卵，并在20℃下46天(+/-7标准误差)后死亡。相差显微镜和透射电子显微镜对感染过程的观察表明，内寄生虫有一个多态的生活史，始于分枝的花椰菜状玫瑰花丛，结束于单一的椭圆形内孢子的发育，一端有乳头，内部结构复杂。内孢子形成与内孢子形成细菌中发现的类似。从形态上看，该寄生虫与1888年从乌克兰马格纳和普列克斯等地分离到的巴氏杆菌有很大的相似之处。自梅奇尼科夫以来，这种寄生虫的鉴定一直是一个持久的难题。通过对16S rDNA分子进行测序，解决了之前对P.ramosa(已被归类为细菌、酵母和原生动物)的混乱的系统发育地位。荧光原位杂交证实，从大盾壳体腔内孢子中获得的16S rDNA序列来源于内寄生虫。最大似然法和最大简约度分析表明，该菌属于真细菌的低G+C革兰氏阳性分支，与结核杆菌、环庚烷脂肪环杆菌和嗜酸杆菌为最近邻分支。这些结果证实了这种寄生虫是一种细菌的说法，并驳斥了之前基于其在放线菌目中的形态复杂性而提出的暂定位置。
The development, life cycle, ultrastructure and phylogenetic position of an obligate, spore-forming endoparasite of Daphnia magna Straus is described. The microparasite was found in the body cavity of three Daphnia species (D. magna, D. pulex and D. longispina) collected in England and Russia during 1992-1994 and maintained in artificial culture by co-cultivation with D. magna. Transmission of the endoparasite occurred horizontally through waterborne spores released from the remains of dead infected hosts. Progeny of infected hosts were never infected, indicating that vertical transmission does not occur. Egg production by infected mothers ceased soon after infection and death ensued after 46 days (+/-7 standard error) at 20 degrees C. Phase contrast light microscopy and transmission electron microscopy of the infection process showed the endoparasite to have a polymorphic life cycle beginning with the appearance of branched 'cauliflower-like' rosettes and ended with the development of single, oval endospores, nippled at one end and with complex internal structure. Endospore formation resembled that found in endospore-forming bacteria. Morphologically the parasite has strong resemblance to the Pasteuria ramosa that Metchnikoff isolated from D. magna and D. pulex in Ukraine and described in 1888. Identification of this parasite has been an enduring puzzle since Metchnikoff. The previously confused phylogenetic position of P. ramosa (it has been classified as bacterium, yeast and protozoa) was resolved by sequencing the 16S rDNA molecule. Fluorescent in situ hybridizations confirmed that the 16S rDNA sequence obtained from the spores within the D. magna body cavity originated from the endoparasite. Maximum likelihood and maximum parsimony analysis showed that P. ramosa belongs to the low G+C Gram positive branch of the eubacteria and resides within a clade containing Bacillus tusciae, Alicyclobacillus cycloheptanicus and A. acidocaldarius as its nearest neighbours. These results confirm suggestions that this parasite is a bacterium and refute its previous tentative placement based on its morphological complexity among the Actinomycetales.