Conjugation is necessary for a bacterial plasmid to survive under protozoan predation

Horizontal gene transfer by conjugative plasmids plays a critical role in the evolution of antibiotic resistance. Interactions between bacteria and other organisms can affect the persistence and spread of conjugative plasmids. Here we show that protozoan predation increased the persistence and spread of the antibiotic resistance plasmid RP4 in populations of the opportunist bacterial pathogen Serratia marcescens. A conjugation-defective mutant plasmid was unable to survive under predation, suggesting that conjugative transfer is required for plasmid persistence under the realistic condition of predation. These results indicate that multi-trophic interactions can affect the maintenance of conjugative plasmids with implications for bacterial evolution and the spread of antibiotic resistance genes.

共轭性质粒（conjugative plasmids）介导的水平基因转移在抗生素耐药性演化中发挥关键作用。细菌与其他生物间的相互作用可影响共轭性质粒的存留与传播。本研究显示，原生动物捕食（protozoan predation）可提升机会致病菌粘质沙雷氏菌（Serratia marcescens）种群中抗生素耐药性质粒RP4的存留与传播能力。共轭功能缺陷型突变质粒无法在捕食条件下存活，这表明在捕食这一真实环境条件下，共轭转移是质粒存留的必要条件。本研究结果表明，多营养级相互作用（multi-trophic interactions）可影响共轭性质粒的维持，这对细菌演化以及抗生素耐药基因的传播具有重要启示意义。