Campylobacter fetus is currently classified into three main subspecies, but only two of these, C. fetus subspecies fetus and C. fetus subsp. venerealis originate principally from ruminants where they inhabit different niches and cause distinct pathogenicity. Their importance as pathogens in international trade and reporting is also different yet the criteria defining these properties have never been fully substantiated nor understood. The situation is further compromised because the ability to differentiate between these two closely related C. fetus subspecies has traditionally been performed by phenotypic characterisation of isolates, methods which are limited in scope, time-consuming, tedious, and often yield inconsistent results, thereby leading to isolate misidentification. The development of robust genetic markers that could enable rapid discrimination between C. fetus subsp. fetus and subsp. venerealis has also been challenging due to limited differences in the gene complement of their genomes, high levels of sequence repetition, the small number of closed genome sequences available and the lack of standardisation of the discriminatory biochemical tests employed for comparative purposes. To yield a better understanding of the genomic differences that define these C. fetus strains, seven isolates were exhaustively characterised phenotypically and genetically and compared with seven previously well characterised isolates. Analysis of these 14 C. fetus samples clearly illustrated that adaption by C. fetus subsp. venerealis to the bovine reproductive tract correlated with increasing genome length and plasticity due to the acquisition and propagation of several mobile elements including prophages, transposons and plasmids harbouring virulence factors. Significant differences in the repertoire of the CRISPR (clustered regularly interspersed short palindromic repeats)-cas system of all C. fetus strains was also found. We therefore suggest that a deficiency in this adaptive immune system may have permitted the emergence of extensive genome plasticity and led to changes in host tropism through gene disruption and/or changes in gene expression. Notable differences in the sub-species complement of DNA adenine methylase genes may also have an impact. These data will facilitate future studies to better understand the precise genetic differences that underlie the phenotypic and virulence differences between these animal pathogens and may identify additional markers useful for diagnosis and sub-typing.

中文翻译：

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对十四个具有充分特征的哺乳动物相关弯曲杆菌胎儿分离株的比较表明，防御机制的丧失有助于高基因组可塑性和亚种进化

胎儿弯曲杆菌目前被分为三个主要的亚种，但是其中只有两个，即C.胎儿亚种胎儿和C.胎儿亚种。委内瑞拉主要来源于反刍动物，它们生活在不同的生态位中，并引起独特的致病性。它们作为病原体在国际贸易和报告中的重要性也有所不同，但定义这些特性的标准从未得到充分证实或理解。由于传统上通过分离株的表型表征，范围有限，费时，乏味且通常产生不一致结果的方法来实现区分这两个紧密相关的胎儿隐孢子虫亚种的能力，因此情况进一步恶化。隔离错误标识。鲁棒的遗传标记的发展，可以快速区分C.胎儿亚种。胎儿和亚种。由于其基因组的基因互补性差异有限，序列重复水平高，可用的封闭基因组序列数量少以及用于比较目的的歧视性生化测试缺乏标准化，因此委内瑞拉也具有挑战性。为了更好地理解定义这些C.胎儿菌株的基因组差异，对7个分离株在表型和遗传上进行了详尽的表征，并与7个先前经过充分表征的分离株进行了比较。对这14个C.胎儿样品的分析清楚地说明了C.胎儿亚种的适应性。牛生殖道的委内瑞拉与基因组长度和可塑性的增加有关，这归因于几种活动元件的获取和繁殖，包括噬菌体，转座子和带有毒力因子的质粒。还发现所有C.胎儿菌株的CRISPR（有簇的定期穿插的短回文重复序列）-cas系统的组成存在显着差异。因此，我们建议这种适应性免疫系统的缺陷可能已允许出现广泛的基因组可塑性，并通过基因破坏和/或基因表达的改变导致宿主嗜性的改变。DNA腺嘌呤甲基化酶基因的亚种补体的显着差异也可能会产生影响。