Department of Microbiology and Virology, The Russian National Research Medical University, 1, Ostrovitjanova St., Moscow 117997, Russia.
Plasmid. 2013 Mar;69(2):146-59. doi: 10.1016/j.plasmid.2012.11.002. Epub 2012 Nov 29.
The analysis of plasmid content in dominant Bacteroidales order intestinal strains isolated from the same child at a 5 year interval identified a 8.9 kb plasmid in Bacteroides uniformis BUN24 strain isolated at age 6 and indistinguishably sized plasmids in the isolates of B. uniformis, B. vulgatus, B. intesinalis, and Parabacteroides distasonis at age 11. We sequenced a B. uniformis BUN24 plasmid, designated pBUN24, and using molecular surveys of diverse species we established that this 8944bp molecule (G+C content 43.5%) represents a novel family of small cryptic Bacteroidales plasmids. The replication region of pBUN24 was experimentally localized to a 1707-bp fragment that includes a putative repA gene, coding for a protein of Rep_3 superfamily of replication proteins of theta-type plasmids preceded by a putative iteron-containing origin of replication. The other open reading frames (ORFs) identified in pBUN24 sequence include a putative tad-ata-type toxin-antitoxin and mobA-mobB mobilization modules, as well as seven additional cryptic ORFs. The interaction of Tad and Ada components demonstrated by a pull-down assay and the toxicity of Tad in Escherichia coli host suggests the functionality of the plasmid addiction module. Re-sequencing of plasmids in two Bacteroides strains isolated at the age of 11 showed 100% nucleotide identity to pBUN24. This data supports the notion that this plasmid is transmissible to other Bacteroidales strains in the natural ecosystem. The possible roles of toxin-antitoxin system and other proteins encoded by pBUN24 in providing an apparent ecological advantage to the plasmid-harbouring strains of a bacterial symbiont in the human gut deserve further investigation.
在相隔 5 年的同一儿童肠道优势拟杆菌目中肠道菌株中分析质粒含量，在 6 岁时分离的均匀拟杆菌 BUN24 菌株中发现了一个 8.9kb 的质粒，而在 11 岁时分离的均匀拟杆菌、脆弱拟杆菌、肠道拟杆菌和副拟杆菌中发现了大小相同的质粒。我们对一个均匀拟杆菌 BUN24 质粒（命名为 pBUN24）进行了测序，通过对不同物种的分子调查，我们确定这个 8944bp 分子（GC 含量为 43.5%）代表了一个新的小型拟杆菌隐秘质粒家族。pBUN24 的复制区被实验定位到一个 1707bp 的片段，该片段包括一个推定的 repA 基因，该基因编码一种 Rep_3 超家族的复制蛋白，前面是一个假定的含有复制起点的内含子。在 pBUN24 序列中鉴定的其他开放阅读框（ORFs）包括一个推定的 tad-ata 型毒素-抗毒素和 mobA-mobB 移动模块，以及另外七个隐匿的 ORFs。通过下拉测定证明了 Tad 和 Ada 组件的相互作用，以及 Tad 在大肠杆菌宿主中的毒性，表明了质粒成瘾模块的功能。在 11 岁时分离的两个拟杆菌菌株中的质粒重新测序显示与 pBUN24 的核苷酸完全一致。这一数据支持了这样一种观点，即这种质粒可以在自然生态系统中传播到其他拟杆菌菌株。进一步的研究应该关注 pBUN24 编码的毒素-抗毒素系统和其他蛋白在为携带质粒的细菌共生体菌株提供明显生态优势方面的可能作用。
