PDF(Pubmed)
Abstract：
BACKGROUND: The obligate intracellular bacterial family Chlamydiaceae comprises a number of different species that cause disease in various vertebrate hosts including humans. Chlamydia suis, primarily found in the gastrointestinal tract of pigs, is the only species of the Chlamydiaceae family to have naturally gained tetracycline resistance (TetR), through a genomic island (Tet-island), integrated into the middle of chromosomal invasin-like gene inv. Previous studies have hypothesised that the uptake of the Tet-island from a host outside the Chlamydiaceae family was a unique event, followed by spread among C. suis through homologous recombination. In vitro recombination studies have shown that Tet-island exchange between C. suis strains is possible. Our aim in this study was to gain a deeper understanding of the interclade recombination of the Tet-island, among currently circulating C. suis field strains compared to in vitro-generated recombinants, using published whole genome sequences of C. suis field strains (n = 35) and in vitro-generated recombinants (n = 63).
RESULTS: We found that the phylogeny of inv better reflected the phylogeny of the Tet-island than that of the whole genome, supporting recombination rather than site-specific insertion as the means of transfer. There were considerable differences between the distribution of recombinations within in vitro-generated strains compared to that within the field strains. These differences are likely because in vitro-generated recombinants were selected for a tetracycline and rifamycin/rifampicin resistant background, leading to the largest peak of recombination across the Tet-island. Finally, we found that interclade recombinations across the Tet-island were more variable in length downstream of the Tet-island than upstream.
CONCLUSIONS: Our study supports the hypothesis that the occurrence of TetR strains in both clades of C. suis came about through interclade recombination after a single ancestral horizontal gene transfer event.
RESULTS: We found that the phylogeny of inv better reflected the phylogeny of the Tet-island than that of the whole genome, supporting recombination rather than site-specific insertion as the means of transfer. There were considerable differences between the distribution of recombinations within in vitro-generated strains compared to that within the field strains. These differences are likely because in vitro-generated recombinants were selected for a tetracycline and rifamycin/rifampicin resistant background, leading to the largest peak of recombination across the Tet-island. Finally, we found that interclade recombinations across the Tet-island were more variable in length downstream of the Tet-island than upstream.
CONCLUSIONS: Our study supports the hypothesis that the occurrence of TetR strains in both clades of C. suis came about through interclade recombination after a single ancestral horizontal gene transfer event.
摘要：
背景:专性细胞内细菌衣原体科包括许多在包括人类在内的各种脊椎动物宿主中引起疾病的不同物种。猪链球菌衣原体,主要在猪的胃肠道中发现，是衣原体科中唯一自然获得四环素抗性（TetR）的物种，通过基因组岛（Tet岛），整合到染色体侵入素样基因inv的中间。先前的研究假设从衣原体科以外的宿主摄取Tet岛是一个独特的事件，然后通过同源重组在猪链球菌之间传播。体外重组研究表明，猪链球菌菌株之间的Tet-岛交换是可能的。我们在这项研究中的目的是更深入地了解Tet岛的相互重组，与体外产生的重组体相比，目前正在循环的猪链球菌领域菌株，使用已发表的猪链球菌田株（n=35）和体外产生的重组体（n=63）的全基因组序列。
结果：我们发现inv的系统发育比全基因组的系统发育更能反映Tet岛的系统发育，支持重组而不是位点特异性插入作为转移手段。与田间菌株相比，体外产生的菌株中重组的分布存在相当大的差异。这些差异可能是因为体外产生的重组体被选择用于四环素和利福霉素/利福平抗性背景。导致整个Tet岛的最大重组峰。最后,我们发现，整个Tet岛的交错重组在Tet岛下游的长度比上游的长度变化更大。
结论：我们的研究支持这样的假设，即在单个祖先水平基因转移事件后，TetR菌株在猪的两个分支中的发生是通过相互重组来实现的。
结果：我们发现inv的系统发育比全基因组的系统发育更能反映Tet岛的系统发育，支持重组而不是位点特异性插入作为转移手段。与田间菌株相比，体外产生的菌株中重组的分布存在相当大的差异。这些差异可能是因为体外产生的重组体被选择用于四环素和利福霉素/利福平抗性背景。导致整个Tet岛的最大重组峰。最后,我们发现，整个Tet岛的交错重组在Tet岛下游的长度比上游的长度变化更大。
结论：我们的研究支持这样的假设，即在单个祖先水平基因转移事件后，TetR菌株在猪的两个分支中的发生是通过相互重组来实现的。
