Analysis of a novel 8.9 kb cryptic plasmid from Bacteroides uniformis, its long-term stability and spread within human microbiota

作者：Shkoporov Andrei N^*; Khokhlova Ekaterina V; Kulagina Elena V; Smeianov Vladimir V; Kuchmiy Anna A; Kafarskaya Lyudmila I; Efimov Boris A

来源：Plasmid, 2013, 69(2): 146-159.

DOI：10.1016/j.plasmid.2012.11.002

• Bacteroides
• Plasmid
• Theta replication
• Addiction module
• Conjugation
• Intestinal microbiota

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 umformis 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 8944 bp 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 coil 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.

• 出版日期2013-3