Data from: Ecological and genetic determinants of plasmid distribution in Escherichia coli

Bacterial plasmids are important carriers of virulence and antibiotic resistance genes. Nevertheless, little is known of the determinants of plasmid distribution in bacterial populations. Here the factors affecting the diversity and distribution of the large plasmids of Escherichia coli were explored in cattle grazing on semi-natural grassland, a set of populations with low frequencies of antibiotic resistance genes. Critically, the population genetic structure of bacterial hosts was chararacterized. This revealed structured E. coli populations with high diversity between sites and individuals but low diversity within cattle hosts. Plasmid profiles, however, varied considerably within the same E. coli genotype. Both ecological and genetic factors affected plasmid distribution: plasmid profiles were affected by site, E. coli diversity, E. coli genotype and the presence of other large plasmids. Notably 3/26 E. coli serotypes accounted for half the observed plasmid-free isolates indicating that within species variation can substantially affect carriage of the major conjugative plasmids. The observed population structure suggest that most of the opportunities for within species plasmid transfer occur between different individuals of the same genotype and support recent experimental work indicating that plasmid–host coevolution, and epistatic interactions on fitness costs are likely to be important in determining occupancy.

细菌质粒是携带毒力与抗生素抗性基因的重要载体。然而，目前学界对细菌种群中质粒分布的决定因素仍知之甚少。本研究针对栖息于半天然草原的牛群展开探究，该种群的抗生素抗性基因频率较低，旨在明确影响大肠杆菌（Escherichia coli）大质粒多样性与分布的各类因素。研究关键之处在于对细菌宿主的种群遗传结构进行了表征。结果显示，大肠杆菌种群存在明显结构分化：不同采样位点与宿主个体间的大肠杆菌多样性较高，但单个牛宿主体内的大肠杆菌多样性较低。不过，同一大肠杆菌基因型内的质粒谱却存在显著差异。生态与遗传因素均会对质粒分布产生影响：质粒谱受采样位点、大肠杆菌多样性、大肠杆菌基因型以及其他大质粒存在情况的共同调控。值得注意的是，26种大肠杆菌血清型中有3种占了无质粒分离株总数的一半，这表明物种内的变异可显著影响主要接合性质粒的携带情况。本研究观测到的种群结构表明，种内质粒转移的主要发生场景为同一基因型的不同个体之间，同时也佐证了近期的实验研究——即质粒-宿主协同进化以及适合度代价相关的上位相互作用，在决定质粒定植情况中可能发挥关键作用。