AmpI Functions as an Iron Exporter To Alleviate β-Lactam-Mediated Reactive Oxygen Species Stress in .

is an organism with a remarkable capacity for drug resistance with several antibiotic resistance determinants in its genome. genome codes for L1 and L2, responsible for intrinsic β-lactam resistance. The Smlt3721 gene (denoted ), located downstream of the L2 gene, encodes an inner membrane protein. The existence of an L2 gene- operon was verified by reverse transcription-PCR (RT-PCR). For aerobically grown KJ, inactivation of downregulated siderophore synthesis and iron acquisition systems and upregulated the iron storage system, as demonstrated by a transcriptome assay, suggesting that AmpI is involved in iron homeostasis. Compared with the wild-type KJ, an mutant had an elevated intracellular iron level, as revealed by inductively coupled plasma mass spectrometry (ICP-MS) analysis, and increased sensitivity to HO, verifying the role of AmpI as an iron exporter. The β-lactam stress increased the intracellular reactive oxygen species (ROS) level and induced the expression of the L1 gene and L2 gene- operon. Compared to its own parental strain, the mutant had reduced growth in β-lactam-containing medium, and the mutant viability was improved after complementation with plasmid pAmpI in either a β-lactamase-positive or β-lactamase-negative genetic background. Collectively, upon challenge with β-lactam, the inducibly expressed L1 and L2 β-lactamases contribute to β-lactam resistance by hydrolyzing β-lactam. AmpI functions as an iron exporter participating in rapidly weakening β-lactam-mediated ROS toxicity. The L1 gene and L2 gene- operon enable to effectively cope with β-lactam-induced stress.