Table_2_A Plasmid With Conserved Phage Genes Helps Klebsiella pneumoniae Defend Against the Invasion of Transferable DNA Elements at the Cost of Reduced Virulence.DOCX

Klebsiella pneumoniae exhibits extensive phenotypic and genetic diversity. Higher plasmid loads in the cell were supposed to play an key role in its genome diversity. Although some plasmids are widely distributed in Kp populations, they are poorly recognized. A plasmid named p2 in strain Kp1604 was predicted to be an intact prophage like Salmonella phage SSU5. However, our study showed that p2 was specifically packaged into membrane vesicles (MVs) rather than phage particles triggered by mitomycin C and subinhibitory concentrations of antibiotics. p2-minus mutant Kp1604Δp2 did not affect MV production. Compared with Kp1604, the capacity of plasmid uptake and the amount of phage burst of Kp1604Δp2 were improved. Moreover, virulence of Kp1604Δp2 also increased. Our results indicated that p2 could contribute to the host defense against the invasion of transferable DNA elements at the cost of reduced virulence. Further study on the mechanism will help us understand how it provides adaptive phenotypes to host evolution.

肺炎克雷伯菌（Klebsiella pneumoniae）具有广泛的表型与遗传多样性。既往研究认为细胞内较高的质粒载量是其基因组多样性的关键驱动因素。尽管部分质粒在肺炎克雷伯菌种群中广泛分布，但目前对其认知仍较为有限。菌株Kp1604中的p2质粒曾被预测为与沙门氏菌噬菌体SSU5（Salmonella phage SSU5）类似的完整前噬菌体。然而本研究显示，在丝裂霉素C（mitomycin C）与亚抑菌浓度抗生素诱导条件下，p2质粒并未被包装为噬菌体颗粒，而是特异性地被包裹进膜囊泡（membrane vesicles, MVs）。p2缺失突变株Kp1604Δp2的膜囊泡产生未受影响；与亲本菌株Kp1604相比，该突变株的质粒摄取能力与噬菌体裂解量均显著提升，且毒力亦有所增强。本研究结果表明，p2质粒可通过降低宿主毒力的代价，协助宿主抵御可转移DNA元件的入侵。对其具体作用机制开展进一步研究，将有助于阐明该质粒如何为宿主进化提供适应性表型。