The data underlying S10 Fig.

Increasing bacterial resistance to colistin, a vital last-resort antibiotic, is an urgent challenge. Previous studies have shown that Mg2+ depletion enables Pseudomonas aeruginosa to become resistant to colistin. Here, we show that magnesium sequestration by Candida albicans also enables P. aeruginosa to evolve a nearly hundredfold higher level of colistin resistance through genetic changes in lipid A biosynthesis-modification pathways and a putative magnesium transporter. These mutations synergize with the Mg2+-sensing PhoPQ two-component signaling system to remodel lipid A structures of the bacterial outer membrane in previously uncharacterized ways. One predominant mutational pathway involves early mutations in htrB2, a non-essential gene involved in lipid A biosynthesis, which enhances resistance but compromises outer membrane integrity, resulting in fitness costs and increased susceptibility to other antibiotics. A second pathway achieves increased colistin resistance independently of htrB2 mutations without compromising membrane integrity. In both cases, reduced colistin binding to the bacterial membrane underlies resistance. Our findings reveal that Mg2+ scarcity triggers novel evolutionary trajectories, leading to extremely high colistin resistance in P. aeruginosa.

细菌对作为关键最后一线抗生素的多粘菌素（colistin）的耐药性不断攀升，是一项亟待解决的紧迫挑战。既往研究证实，镁离子（Mg²+）匮乏可使铜绿假单胞菌（Pseudomonas aeruginosa）获得对多粘菌素的耐药性。本研究发现，白色念珠菌（Candida albicans）介导的镁离子螯合作用，同样可促使铜绿假单胞菌通过脂质A（lipid A）生物合成修饰通路及假定镁离子转运蛋白的遗传变异，进化出近百倍水平的多粘菌素耐药性。上述突变与感知Mg²+的PhoPQ双组分信号系统协同作用，以此前未被阐明的方式重塑细菌外膜的脂质A结构。一条主要的突变通路涉及htrB2基因的早期突变：该基因为脂质A生物合成相关的非必需基因，其突变可增强耐药性，但会破坏外膜完整性，进而引发适合度代价，并提升对其他抗生素的敏感性。第二条突变通路可不依赖htrB2基因突变即可提升多粘菌素耐药性，且不会破坏膜完整性。两种途径下，多粘菌素与细菌膜的结合能力降低均是耐药性产生的核心机制。本研究结果揭示，镁离子匮乏可触发全新的进化轨迹，最终使铜绿假单胞菌获得极高水平的多粘菌素耐药性。