Department of Pathology and Infectious Diseases, School of Veterinary Medicine, University of Surrey, Guildford, UK.
BMC Genomics. 2020 Apr 19;21(1):314. doi: 10.1186/s12864-020-6704-z.
Campylobacter jejuni and Campylobacter coli are major global causes of bacterial gastroenteritis. Whilst several individual colonisation and virulence factors have been identified, our understanding of their role in the transmission, pathogenesis and ecology of Campylobacter has been hampered by the genotypic and phenotypic diversity within C. jejuni and C. coli. Autotransporter proteins are a family of outer membrane or secreted proteins in Gram-negative bacteria such as Campylobacter, which are associated with virulence functions. In this study we have examined the distribution and predicted functionality of the previously described capC and the newly identified, related capD autotransporter gene families in Campylobacter.
Two capC-like autotransporter families, designated capC and capD, were identified by homology searches of genomes of the genus Campylobacter. Each family contained four distinct orthologs of CapC and CapD. The distribution of these autotransporter genes was determined in 5829 C. jejuni and 1347 C. coli genomes. Autotransporter genes were found as intact, complete copies and inactive formats due to premature stop codons and frameshift mutations. Presence of inactive and intact autotransporter genes was associated with C. jejuni and C. coli multi-locus sequence types, but for capC, inactivation was independent from the length of homopolymeric tracts in the region upstream of the capC gene. Inactivation of capC or capD genes appears to represent lineage-specific gene decay of autotransporter genes. Intact capC genes were predominantly associated with the C. jejuni ST-45 and C. coli ST-828 generalist lineages. The capD3 gene was only found in the environmental C. coli Clade 3 lineage. These combined data support a scenario of inter-lineage and interspecies exchange of capC and subsets of capD autotransporters.
In this study we have identified two novel, related autotransporter gene families in the genus Campylobacter, which are not uniformly present and exhibit lineage-specific associations and gene decay. The distribution and decay of the capC and capD genes exemplifies the erosion of species barriers between certain lineages of C. jejuni and C. coli, probably arising through co-habitation. This may have implications for the phenotypic variability of these two pathogens and provide opportunity for new, hybrid genotypes to emerge.
空肠弯曲菌和大肠弯曲菌是全球主要的细菌食源性肠胃炎致病菌。虽然已经确定了一些单独的定植和毒力因子，但由于空肠弯曲菌和大肠弯曲菌的基因型和表型多样性，我们对它们在弯曲菌的传播、发病机制和生态学中的作用的理解一直受到阻碍。自转运蛋白是革兰氏阴性菌（如弯曲菌）中一类外膜或分泌蛋白家族，与毒力功能有关。在这项研究中，我们研究了先前描述的 capC 和新发现的相关 capD 自转运体基因家族在弯曲菌中的分布和预测功能。
通过对弯曲菌属基因组的同源性搜索，鉴定了两个 capC 样自转运体家族，分别命名为 capC 和 capD。每个家族都包含四个不同的 CapC 和 CapD 直系同源物。通过对 5829 株空肠弯曲菌和 1347 株大肠弯曲菌基因组的检测，确定了这些自转运体基因的分布。自转运体基因以完整、完整的拷贝和由于提前终止密码子和移码突变而处于非活性形式存在。由于存在无活性和完整的自转运体基因，它们与空肠弯曲菌和大肠弯曲菌多位点序列类型相关，但对于 capC 而言，失活与 capC 基因上游同源性高的区域无关。capC 或 capD 基因的失活似乎代表了自转运体基因的谱系特异性基因衰减。完整的 capC 基因主要与空肠弯曲菌 ST-45 和大肠弯曲菌 ST-828 通用谱系相关。capD3 基因仅在环境大肠弯曲菌 clade 3 谱系中发现。这些综合数据支持 capC 和 capD 自转运体亚群在谱系间和种间交换的情景。
在这项研究中，我们在弯曲菌属中鉴定了两个新的、相关的自转运体基因家族，它们不是普遍存在的，并且表现出谱系特异性的关联和基因衰减。capC 和 capD 基因的分布和衰减说明了某些空肠弯曲菌和大肠弯曲菌谱系之间种间屏障的侵蚀，这可能是通过共生而产生的。这可能对这两种病原体的表型变异性产生影响，并为新的、杂交基因型的出现提供机会。
