Alphaproteobacteria are typically characterized by a multipartite genome organization with a chromosome, stable chromids and accessory plasmids. Extrachromosomal elements determine the lifestyle of roseobacters and their horizontal transfer was previously correlated with rapid adaptations to novel ecological niches. We characterized the distribution and biology of a novel Rhodobacteraceae-specific plasmid type that was designated RepC_soli according to its diagnostic solitary replicase. This low copy number replicon exhibits an exceptional stability, which is likely ensured by non-canonical separate parA and parB partitioning genes. RepC_soli plasmids occur frequently in the surface-associated marine genus Phaeobacter and comparative genome analyses revealed the emergence of four compatibility groups. The universal presence of conserved type IV secretion systems in RepC_soli plasmids is indicative of their recurrent mobilization, a prediction that was experimentally validated by conjugation of the 57 kb Phaeobacter inhibens P72 plasmid (pP72_e) over genus borders. RepC_soli plasmids harbour a diverse collection of beneficial genes including transporters for heavy metal detoxification, prokaryotic defence systems and a conspicuous abundance of antibiotic resistance genes. The pP72_e-encoded efflux pump FloR conferred an about 50-fold increase of resistance against chloramphenicol. Its specific occurrence in Phaeobacter likely reflects a genetic footprint of (former) antimicrobial use in marine aquaculture.

中文翻译：

---

RepC_soli：一种新型的红杆菌科混杂质粒类型介导海洋中抗生素抗性的水平转移

Alphaproteobacteria的典型特征是具有染色体、稳定染色质和辅助质粒的多部分基因组组织。染色体外元素决定了玫瑰杆菌的生活方式，它们的水平转移以前与对新生态位的快速适应有关。我们描述了一种新的红杆菌科特异性质粒类型的分布和生物学特征，根据其诊断性孤立复制酶命名为 RepC_soli。这种低拷贝数复制子表现出异常的稳定性，这可能是由非规范的单独parA和parB分区基因确保的。RepC_soli 质粒经常出现在表面相关的海洋菌属Phaeobacter 中比较基因组分析揭示了四个相容性组的出现。RepC_soli 质粒中普遍存在保守的 IV 型分泌系统表明它们会反复动员，这一预测已通过 57 kb抑制噬菌体P72 质粒 (pP72_e) 在属边界上的缀合得到实验验证。RepC_soli 质粒包含多种有益基因，包括重金属解毒转运蛋白、原核防御系统和大量抗生素抗性基因。pP72_e 编码的外排泵 FloR 使对氯霉素的抗性增加了约 50 倍。其具体存在于嗜酸杆菌中 可能反映了海洋水产养殖中（前）抗菌剂使用的遗传足迹。