类立克次氏体细菌内共生体在其圆口螺科宿主 Plagiorchis elegans 的无性繁殖阶段，在自然感染的圆口螺中的传播率。
Transmission rates of the bacterial endosymbiont, Neorickettsia risticii, during the asexual reproduction phase of its digenean host, Plagiorchis elegans, within naturally infected lymnaeid snails.
机构信息
Department of Biology, University of North Dakota, 10 Cornell St,, Grand Forks, North Dakota 58202, USA.
出版信息
Parasit Vectors. 2013 Oct 22;6:303. doi: 10.1186/1756-3305-6-303.
BACKGROUND
Neorickettsia are obligate intracellular bacterial endosymbionts of digenean parasites present in all lifestages of digeneans. Quantitative information on the transmission of neorickettsial endosymbionts throughout the complex life cycles of digeneans is lacking. This study quantified the transmission of Neorickettsia during the asexual reproductive phase of a digenean parasite, Plagiorchis elegans, developing within naturally parasitized lymnaeid pond snails.
METHODS
Lymnaea stagnalis snails were collected from 3 ponds in Nelson County, North Dakota and screened for the presence of digenean cercariae. Cercariae were identified to species by PCR and sequencing of the 28S rRNA gene. Neorickettsia infections were initially detected using nested PCR and sequencing of a partial 16S rRNA gene of pooled cercariae shed from each parasitized snail. Fifty to 100 single cercariae or sporocysts were isolated from each of six parasitized snails and tested for the presence of Neorickettsia using nested PCR to estimate the efficiency at which Neorickettsia were transmitted to cercariae during asexual development of the digenean.
RESULTS
A total of 616 L. stagnalis were collected and 240 (39%) shed digenean cercariae. Of these, 18 (8%) were Neorickettsia-positive. Six Neorickettsia infections were selected to determine the transmission efficiency of Neorickettsia from mother to daughter sporocyst and from daughter sporocyst to cercaria. The prevalence of neorickettsiae in cercariae varied from 11 to 91%. The prevalence of neorickettsiae in sporocysts from one snail was 100%.
CONCLUSION
Prevalence of Neorickettsia infection in cercariae of Plagiorchis elegans was variable and never reached 100%. Reasons for this are speculative, however, the low prevalence of Neorickettsia observed in some of our samples (11 to 52%) differs from the high prevalence of other, related bacterial endosymbionts, e.g. Wolbachia in Wolbachia-dependent filariid nematodes, where the prevalence among progeny is universally 100%. This suggests that, unlike the Wolbachia-filaria relationship, the Neorickettsia-digenean relationship is not obligatory mutualism. Our study represents the first quantitative estimate of the Neorickettsia transmission through the asexual phase of the digenean life cycle.
背景
Neorickettsia 是寄生在双壳类寄生虫所有生活阶段的专性细胞内细菌内共生体。缺乏关于 Neorickettsia 内共生体在双壳类寄生虫复杂生活史中的传播的定量信息。本研究通过定量检测 Plagiorchis elegans 双壳类寄生虫的无性生殖阶段，即在自然感染的腹足纲池塘蜗牛中发育过程中的 Neorickettsia 内共生体的传播。
方法
从北达科他州纳尔逊县的 3 个池塘中收集了 Stagnicola 蜗牛并对其进行了双壳类尾蚴的存在情况进行筛查。通过 PCR 和 28S rRNA 基因测序鉴定尾蚴的种类。最初使用巢式 PCR 和从每个受感染蜗牛释放的 pooled cercariae 的部分 16S rRNA 基因测序来检测 Neorickettsia 感染。从 6 只受感染的蜗牛中，每只蜗牛分别分离出 50 到 100 个单尾蚴或孢囊，并使用巢式 PCR 检测 Neorickettsia 的存在情况，以估计 Neorickettsia 在双壳类寄生虫无性发育过程中向尾蚴传播的效率。
结果
共收集了 616 只 L. stagnalis，其中 240 只（39%）释放了双壳类尾蚴。其中，18 只（8%）为 Neorickettsia 阳性。选择了 6 种 Neorickettsia 感染来确定 Neorickettsia 从母孢囊到子孢囊以及从子孢囊到尾蚴的传播效率。尾蚴中 Neorickettsia 的流行率从 11%到 91%不等。一只蜗牛的孢囊中的 Neorickettsia 流行率为 100%。
结论
Plagiorchis elegans 尾蚴的 Neorickettsia 感染流行率各不相同，从未达到 100%。造成这种情况的原因尚不确定，但与其他相关的细菌内共生体（例如 Wolbachia 依赖性丝虫中的 Wolbachia）相比，我们的一些样本中观察到的 Neorickettsia 低流行率（11%至 52%）不同，这些内共生体在后代中的流行率普遍为 100%。这表明，与 Wolbachia-filaria 关系不同，Neorickettsia-双壳类寄生虫关系不是强制性的共生关系。我们的研究代表了通过双壳类寄生虫生活史的无性阶段定量估计 Neorickettsia 传播的首次尝试。
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