Lin Mingqun, Bachman Katherine, Cheng Zhihui, Daugherty Sean C, Nagaraj Sushma, Sengamalay Naomi, Ott Sandra, Godinez Al, Tallon Luke J, Sadzewicz Lisa, Fraser Claire, Dunning Hotopp Julie C, Rikihisa Yasuko
Department of Veterinary Biosciences, The Ohio State University, 1925 Coffey Road, Columbus, OH, 43210, USA.
Institute for Genome Sciences, University of Maryland School of Medicine, 801 W. Baltimore St, Baltimore, MD, 21201, USA.
Microb Biotechnol. 2017 Jul;10(4):933-957. doi: 10.1111/1751-7915.12731. Epub 2017 Jun 6.
Neorickettsia helminthoeca, a type species of the genus Neorickettsia, is an endosymbiont of digenetic trematodes of veterinary importance. Upon ingestion of salmonid fish parasitized with infected trematodes, canids develop salmon poisoning disease (SPD), an acute febrile illness that is particularly severe and often fatal in dogs without adequate treatment. We determined and analysed the complete genome sequence of N. helminthoeca: a single small circular chromosome of 884 232 bp encoding 774 potential proteins. N. helminthoeca is unable to synthesize lipopolysaccharides and most amino acids, but is capable of synthesizing vitamins, cofactors, nucleotides and bacterioferritin. N. helminthoeca is, however, distinct from majority of the family Anaplasmataceae to which it belongs, as it encodes nearly all enzymes required for peptidoglycan biosynthesis, suggesting its structural hardiness and inflammatory potential. Using sera from dogs that were experimentally infected by feeding with parasitized fish or naturally infected in southern California, Western blot analysis revealed that among five predicted N. helminthoeca outer membrane proteins, P51 and strain-variable surface antigen were uniformly recognized. Our finding will help understanding pathogenesis, prevalence of N. helminthoeca infection among trematodes, canids and potentially other animals in nature to develop effective SPD diagnostic and preventive measures. Recent progresses in large-scale genome sequencing have been uncovering broad distribution of Neorickettsia spp., the comparative genomics will facilitate understanding of biology and the natural history of these elusive environmental bacteria.
赫氏新立克次氏体（Neorickettsia helminthoeca）是新立克次氏体属的模式种，是具有兽医重要性的复殖吸虫的内共生体。犬科动物摄食感染了吸虫的鲑科鱼类后，会患上鲑鱼中毒病（SPD），这是一种急性发热性疾病，对未经适当治疗的犬类来说尤为严重，且往往致命。我们测定并分析了赫氏新立克次氏体的完整基因组序列：一个884232 bp的单条小环状染色体，编码774种潜在蛋白质。赫氏新立克次氏体无法合成脂多糖和大多数氨基酸，但能够合成维生素、辅因子、核苷酸和细菌铁蛋白。然而，赫氏新立克次氏体与其所属的无形体科的大多数成员不同，因为它编码肽聚糖生物合成所需的几乎所有酶，这表明其结构坚固性和炎症潜力。使用通过喂食感染寄生虫的鱼而实验感染或在南加州自然感染的犬的血清，蛋白质免疫印迹分析显示，在五种预测的赫氏新立克次氏体外膜蛋白中，P51和菌株可变表面抗原能被一致识别。我们的发现将有助于理解赫氏新立克次氏体感染在吸虫、犬科动物以及自然界中其他潜在动物中的发病机制和流行情况，从而制定有效的鲑鱼中毒病诊断和预防措施。大规模基因组测序的最新进展揭示了新立克次氏体属的广泛分布，比较基因组学将有助于理解这些难以捉摸的环境细菌的生物学特性和自然史。
