Institute for Molecular Bioscience (IMB), The University of Queensland, Brisbane, Queensland, Australia.
School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, Australia.
PLoS Genet. 2023 Jun 22;19(6):e1010773. doi: 10.1371/journal.pgen.1010773. eCollection 2023 Jun.
Plasmids are major drivers of increasing antibiotic resistance, necessitating an urgent need to understand their biology. Here we describe a detailed dissection of the molecular components controlling the genetics of I-complex plasmids, a group of antibiotic resistance plasmids found frequently in pathogenic Escherichia coli and other Enterobacteriaceae that cause significant human disease. We show these plasmids cluster into four distinct subgroups, with the prototype IncI1 plasmid R64 subgroup displaying low nucleotide sequence conservation to other I-complex plasmids. Using pMS7163B, an I-complex plasmid distantly related to R64, we performed a high-resolution transposon-based genetic screen and defined genes involved in replication, stability, and conjugative transfer. We identified the replicon and a partitioning system as essential for replication/stability. Genes required for conjugation included the type IV secretion system, relaxosome, and several uncharacterised genes located in the pMS7163B leading transfer region that exhibited an upstream strand-specific transposon insertion bias. The overexpression of these genes severely impacted host cell growth or reduced fitness during mixed competitive growth, demonstrating that their expression must be controlled to avoid deleterious impacts. These genes were present in >80% of all I-complex plasmids and broadly conserved across multiple plasmid incompatibility groups, implicating an important role in plasmid dissemination.
质粒是增加抗生素耐药性的主要驱动力，因此迫切需要了解它们的生物学特性。在这里，我们详细描述了控制 I 型复合质粒遗传的分子成分，这些质粒是一组常见于致病性大肠杆菌和其他肠杆菌科的抗生素耐药质粒，它们会导致严重的人类疾病。我们发现这些质粒可以分为四个不同的亚群，原型 IncI1 质粒 R64 亚群与其他 I 型复合质粒的核苷酸序列保守性较低。我们使用与 R64 关系较远的 I 型复合质粒 pMS7163B 进行了高分辨率转座子遗传筛选，并定义了与复制、稳定性和接合转移相关的基因。我们确定了复制子和分配系统是复制/稳定性所必需的。接合所需的基因包括 IV 型分泌系统、松弛酶和几个位于 pMS7163B 起始转移区的未被表征的基因，该起始转移区表现出上游链特异性转座子插入偏倚。这些基因的过表达严重影响宿主细胞的生长或在混合竞争生长期间降低适应性，表明它们的表达必须受到控制，以避免有害影响。这些基因存在于超过 80%的所有 I 型复合质粒中，并在多个质粒不相容群中广泛保守，这表明它们在质粒传播中起着重要作用。
